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This heap of horticutural hash is a tasty blend of spicy irreverance and nutritious facts. It was originally published in the June 2022 issue of Cross Pollination, the newsletter of the Halton Region Master Gardeners.
By Bev Wagar, Halton Master Gardener
Horticulture! It sweeps you off your feet, showers you with affection, and sheet-mulches your back yard. But when it moves in—that’s when you realize its suitcases are stuffed with strange nouns and adjectives. Horticulture packs a lot of language!
Oh the dictionary writers would have us believe it’s the “art of cultivating plants”, often with a patina of science or at least a good dollop of seriousness. But the truth is that horticulture’s wordy baggage can suck the joy out of the simple act of mucking about in the soil.
All that Latin! All those syllables!
Before you throw down your “Complete Gardener’s Dictionary” (Barbara Ellis) or “Botany for Gardeners” (Brian Capon), do try using memory aids or, if you like irony, “mnemonics.” A mnemonic (nuh·mo·nuhk) is a learning technique that helps us retain or remember information. These techniques are based on the observation that, compared to the usual abstract or impersonal methods, the human mind more easily remembers spatial, personal, surprising, physical, sexual, humorous, or otherwise “relatable” information.
Here are a few to get you started.
Phloem. This is an easy one. PhlOem flows. Stuff, in general, flows downwards. Phloem tissue enables the transfer of energy from the top of the tree down to the roots. Unlike trickle-down economics, the good stuff literally phloems down.
Xylem. Xylem are the specialized cells in tree trunks that move water from the root system to the leaves. Quite coincidentally, xylem rhymes with asylum. So imagine you’re in an asylum—some days it’s not that difficult. It’s an old-fashioned asylum with a tall fence, a guard named “Turkle”, and a musty library full of horticultural dictionaries and pronunciation guides. You’ll need to climb up that fence to get out. Xylem moves up. So climb that big fence up out of the as-xylem!
Glabrous. Something glabrous is smooth, with no hairs of any kind, like lilac leaves, or your legs for about two minutes after getting them waxed. Sorry guys—here’s a more inclusive metaphor: Glabrous is glamorous, like Joan Crawford or Lana Turner. Did these glamorous women have fuzzy upper lips? Wierd hairs on their chin? No they did not—they were glabrous.
Rugose. Wrinkly. The leaves on ‘Fireworks’ goldenrod (Solidago rugosa) are rugose. So are the leaves of the mint (genus Mentha) that escaped its container two years ago. Now it’s got an armed bunker in your back yard (see “stolon” below) and demands your unconditional surrender. You rue the day you planted mint—now you rue-those rue-gose leaves.
Stamen. The male fertilizing organ of a flower, typically consisting of a pollen-containing anther and a filament. A stamen often wears bright yellow lipstick and powders his nose, but he’ll always stay (a) man.
Pistil. These are the female organs of a flower, comprising the stigma, style, and ovary. Pistil rhymes with Crystal—your niece the wannabe model who took 583 selfies last year. Crystal’s female organs are hard to forget once they’ve been aimed at you, like pistols, er, pistils.
Dioecious. This word describes plants that have the male and female flowers on different plants. You need two of them, a male and a female, for pollination and proper fruit set or viable seeds. Holly (Ilex) and Spicebush (Lindera) are dioecious shrubs. It’s pronounced “dah·ee·shuhs” as in “Dice! Shush!”, a phrase often heard at casinos and back-room poker games. Just remember that you need two dice—a male and a female. Sometimes they’re hard to tell apart. Look for the one smoking a cigar. That’s the female.
Monoecious. A monoecious plant has both the male and female reproductive organs (flowers or cones) on the same individual. Both sexes are on one plant. The non-intuitive pronunciation (“mah·nee·shuhs”) reminds us of muh-nee (money) which, despite much imaginative googling and two glasses of wine, resists any association with plant reproduction. So look at the spelling instead: “mono” = “one” as in monolith, monopoly, monorail, monologue, monochrome, monogamy, monotony…
Stolon. A stolON is a type of plant root that travels ON top of the soil. Sometimes called “runners”, stolons create new daughter plants when the bud at an apex touches the soil. Examples of stoloniferous plants include: creeping charlie, ajuga, strawberries, and many other plants sometimes used to cover the ground we don’t want to look at.
Rhizome. A rhizome’s home is in the loam. Rhizomes are modified stems that travel horizontally, underground, sending up shoots along their length. Many pernicious weeds spread by rhizomes: quack grass, vinca, lily-of-the valley, that stuff your mother-in-law gave you in 1986. One the worst weeds ever invented, Japanese knotweed, is rhizomatous. Plants with rhizomes proliferate on streets with gullible and generous gardeners. Bettina, for example, used to tell her neighbours “it’s not invasive in my garden” and now no one talks to her.
The horticulture world writhes with pesky nouns and adjectives. Cranky and persnickety, they like to corner you at parties and roll their eyeballs when you forget their names. Summon your courage! Crank up your imagination and devise some mnemonic devices—soon you’ll be ready to face those binomials with confidence and flair. Give it a try!
Bio-degradable, legible, inexpensive, water-resistant, uniform labels that can be produced in quantity. Great for backyard nurseries.
I’m not a tidy gardener and my plants get to do their own thing most of the time. But there’s one inevitable springtime housecleaning chore: removing dozens of plastic plant markers that are dislodged from the soil by frost heave and squirrels. I do re-use them–white electrical tape provides a fresh writing surface–but this year I’m bothered more than usual about the sheer volume of plastic in the garden. Every year I grow hundreds of plants to give away and sell and each pot needs to be labelled. Writing on the plastic, recycled or not, is time consuming and monotonous. Often there’s not enough room for the full botanical name. Using wax pencils (china markers), which are the most indelible for the long term, is especially slow.
So I came up with an improved version of “mass produced” markers that will survive several months of rain and sun, long enough to get seedlings big enough to go to their forever homes.
Here’s what you need:
– craft sticks. Wider ones are better, but regular ones will work
– Mod-Podge, decopage glue, or white glue. Any water-based glue/sealer will do, so long as it dries clear
– small paint brush. You could also just use your finger if you don’t have brushes on hand. Fingers are always on hand 🙂
– a printer and regular printer paper
Follow the captions and photos in the gallery at right. Don’t get too precious about the process– these only need to last a few months. Let the kids help if you don’t mind the extra mess. This is a great indoor project for a rainy day.
This article was originally published in May 2019, in The Point, Crown Point’s community newspaper.
Is something terrible happening to your favourite shrub? Did you make a garden bed last year and everything died? Is your rock-hard soil growing a bumper crop of weeds?
It’s natural for keen gardeners to tackle problems head-on. We want to fix them fast before they get any worse. And, like helicopter parents, we want to help our plants along, even if they’re not showing signs of distress. We want to give them every possible advantage.
Every spring, homeowners, even people with nice established gardens, order a “load of dirt” and spend the next two days schlepping it from the driveway to the garden. Arising from the best intentions, along with a lifetime of consumer habits, the urge to spend our way to garden success is hard to resist.
But we must resist.
Just because it’s one of the few things we can do in April is no reason to do it. Soon it will warm up and the soil will dry out and we can do something other than shovel black stuff onto plants that are just poking their heads up. There are better ways to stay warm in April!
Burning with cabin fever and billboard visions, too often we load up with Big Yellow Bags, little white bags, expensive red bags. We buy treats for our gardens, hoping that, this summer, they’ll finally behave themselves and do what they’re told. But gardens are not consumer items. They scoff at our lazy, puny, and misguided efforts to get them to perform.
Consumer culture permeates modern life. We’re rooted in it and conditioned to expect quick and cheap solutions. Instead of shopping we should take time to observe, analyze, research, diagnose, and understand what’s happening in our gardens.
I have a friend, a non-gardener, who wanted a better front lawn. She lives in an older part of the city, next to a ravine so there are deer, skunks, squirrels, and old trees that make roots and shade. So, having done no research and having only a faint notion (about wanting to “put something on the grass”), she went to Green Horizons / Hamilton Sod and asked for advice. Of course they sent her home with several bags of “black earth” and a bag of fertilizer. When I told her that neither of these were necessary and, if anything, she should have used a light topdressing of compost and overseeded, well she was a little distressed. Her lawn will recover, but what a waste of time it was.
We don’t need products. We need Science. Science tells us how plants function in an ecosystem, how the complex interaction of sunshine, rain, air, mineral-based soil, organic matter, and soil-dwelling organisms, both microscopic and visible, create the conditions for terrestrial life. Biology calls this the carbon cycle. Gardeners call it loam.
And we can’t buy loam. The black earth in the bags is not loam.
Here is what’s in those bags (quoting from the company’s web site): “black loam, peat loam, very-well-decomposed manure and a touch of mineral soil.” I phoned them to get details.
“Black loam” is the anaerobically decomposed remains of ancient grasses and ferns removed from the bottom of deep-water bogs in the Ottawa area. This is what gives the product its dark colour. “Peat loam” is partially decomposed sphagnum moss from peat wetlands in the Turkey Point area. I did not ask where they obtained the “well decomposed manure” but note the use of “decomposed” and not “composted”. This suggests that the manure is not from a managed aerobic process. And, finally, the tiny “mineral soil” portion comes from the sod farm side of the business. So, it’s clear why the product is virtually weed-free. And, although it would likely support microbial life should it encounter any, it is pretty much dead.
A quick note about peat… It is a finite resource and cannot be harvested in a sustainable way. Once the wetland has been destroyed by excavators, there is no going back. The producer may level the ground and plant trees but the wetland is gone forever. As a soil amendment there are far better alternatives to peat: composted manure is probably the best. Composted garden “waste” is also excellent.
Returning to our black earth product, we now shovel the stuff onto the garden, and watch the drainage and growing problems begin. Almost certainly the new “soil” will be different from the existing soil. Anything planted into the soft top layer will have trouble putting down deep roots; once they reach the original soil layer (which is likely to be more dense and compact) they don’t push through. They just go sideways, taking the path of least resistance forced to remain in a biologically inert bathtub of peat
Water, too, will completely saturate the top layer before slowly percolating into the lower layer. It’s simply the physics of the way water travels in soil of different textures. The effect is similar to what happens when we put a raised bed on top of clay: a soggy saturated planting layer perched on top of the native soil at grade.
To create a natural way for water to drain and moisture to wick to the surface we must make a transitional layer by tilling two or three inches of the new soil into the native soil. Then, more can be added. It is well worth the additional effort.
Of course, the better way to avoid these problems is to not add “new” soil in the first place.
Instead of buying stuff to put on our garden we should do what nature does: allow organic matter to decompose in the top few inches of soil. This is the role of leaves—nature’s mulch—that carpet our gardens in the fall. Also, the role of trees that fall and decay into the soil. We can speed this up a bit by chipping the wood and shredding the leaves first. But principle is the same. Organic matter goes on top, in the top few inches.
Soil fauna reproduces and dies so quickly. The microherd both creates and becomes organic matter. They cause channels and pore spaces to open up in the soil, for air and moisture. They are how plant roots are fed in natural systems, in healthy soil. We can’t fake these systems. We can’t buy them. We can provide the right materials, encourage the right conditions, and then we must wait.
Slow gardening, like slow food, has some general guidelines.
Add organic matter. Material such as well-rotted manure, compost, kitchen scraps, or crop residues. Incorporate these lightly into the top six inches of soil–don’t bury them deep. The organisms that do the work of decomposition live where air and moisture are available.
Get something growing. Keep the soil covered with something living for as long as possible. Look into growing “green manure” or “living mulch” plants instead of having bare garden beds, especially over winter. Native grasses have extremely deep roots that, left undisturbed, will travel down up to six feet. Root systems are constantly growing and contracting, sloughing off feeder roots that become food for the microherd, create channels for the movement of water and air and, over time, create what we call good “tilth”– the ability of soil to form sticky crumbs that we love to touch.
Cover thy naked soil with materials that decompose: arborists’ wood chips are a good choice. Straw, hay, and grass clippings can also help. Avoid using mulch made of shredded or chipped wood bark, as well as any mulch made of cedar. These are resistant to decomposition. And, of course, avoid using plastic, landscape cloth and anything else that creates a barrier to rain or air.
Do Not Disturb the soil. Reduce tillage and digging that inverts soil layers. Churning up the habitat of soil-dwelling organisms is harmful to them. Don’t create new soil layers by adding commercial “soil” products.
Right Plant, Right Place. Find plants that will thrive in the soil you’ve got right now. Instead of fretting over creating the right pH for Rhododendrons or trying to fix clay with gypsum, peat, epsom salt, or some other concoction, just get something growing. If you do some research you’ll find there are many uncommon and beautiful plants that will thrive in clay or sand.
Your dream garden is possible. With time, knowledge, care–and no more big bags.
She never did.
Crammed with nudges and winks, this educational piece was originally published in the May 2022 issue of Cross Pollination, the newsletter of the Halton Region Master Gardeners.
By Bev Wagar, Halton Master Gardener
Carrot had been growing beside Tomato for only a few weeks when she realized she didn’t like the guy. In fact, she couldn’t stand him. And couldn’t let the rumours continue.
“It’s not personal, Tom”, she said. “But I think the expectations around our relationship were far too high.” Sadly, Carrot’s attempt at tact did not have the desired effect. Tomato erupted in a flood of sticky tears.
“But… but… You said you loved me!” Although they were just beginning to form, he let a few flowers drop to show the depth of his feelings for her. Tom had never been good at hiding his feelings. He couldn’t help but droop at the slightest thirst and his leaves turned yellow at least provocation.
“I never said that,” Carrot retorted, a bit too quickly. “It was that book and all the humans who read it. Something about ‘companion planting’. Malarcky, all of it, and now I’m stuck here, trying to grow in your shade.”
Tom arched over his unwilling companion with a sad fondness. He’d loved Carrot from the moment they’d met. She’d been planted as a seed, back in late April, and had already been thinned once before Tom got plunked in beside her. Right away he was smitten. And when her soft frilly leaves began tickling his lower stems he became so giddy his leaf axils sprouted six more secondary stems almost overnight.
“The human who planted us had good intentions” said Tomato. “I overheard her talking about all the different plants that are supposed to like or dislike each other. The book was about secrets and mystery—and rules. So many rules! Apparently our human was skeptical about the ‘lack of scientific evidence’ or something like that, but she was going to follow the book’s advice anyway.”
Carrot tossed her curly green locks and shot him one of those looks reserved for naughtly seedlings. She knew Tom wasn’t to blame for the current situation. But she also knew he was a Big Boy, an old hybrid, robust and resistant to many of the diseases his type was prone to. He wasn’t going away and, unless his cage broke, he wouldn’t get any shorter. And they were both in clay, so her root was struggling to get to the usual depth while Tom’s roots did not seem to mind.
“The human’s little experiment is not helping me at all. Most of the bi-peds are nuts anyway” she snarked. “And now you’re getting all crazy, too. Tom, you need to stop telling everyone we’re in love!”
Carrot noticed the stunned look on Tom’s face but kept going. “You think you’re doing me a favour by providing shade? Is that it? Well just because I like it cool doesn’t mean I don’t need sunlight. And Tom, you big lug, you’re hogging it all!”
It had to be her hungry chloroplasts talking, thought Tom. Surely the sweet-scented seedling he adored would not be so cruel.
“Carrie sweetheart, what did I do? Why are you treating me like this?”
She hated that name but kept her composure. She wasn’t finished.
“And what’s with all the fertilizer, especially the nitrogen,” she continued. “That blue powder the humans mix up and douse you with. Well it doesn’t stay on your side. I can’t stand it. Makes my root get all hairy and weird.”
“I had no idea” said Tom. “That stuff is like candy to me. But I wish they’d give me real food, like fish meal or manure or any of those, what do they call them, organic ferts, but I don’t have any choice, do I?”
Carrot softened a bit. They were both stuck in the same garden. Tomato wasn’t a bad plant, just a little thick. Was it the gorgeous fruit that made him so popular? Sometimes Carrot wished she wasn’t so, well, difficult. A little popularity would surely keep the humans from treating her like a useful but dispensable sidekick to that big sauce-monkey overhead. She re-arranged her leaves and tried her best to sound gentle and caring.
“You and I have such different cultural requirements, Tom. Why would the humans think we love each other?”
“Something to do with you repelling insects that are supposed to be attracted to me,” replied Tom. “Or your flowers that are supposed to bring in the ones who eat the insects that eat my leaves. When the humans talk about that stuff it’s all mixed up with moon phases and star positions and something called astro-zoology.”
“A bunch of mystical mumbo jumbo,” Carrot quipped. “But the insect stuff does make sense in a general way, even though most of the little buzzers just want my flowers and those won’t happen until next year, if I even live that long. But what about the here-and-now? You’re so big nobody knows I’m here. What good am I doing you? Besides, I’m the one who’s suffering!”
Tom was about to reach down and tickle her frilly mop-top when they both noticed the Birkenstocks. The human was back! And what was that in her hand? A garden fork! Carrot knew her time had come. Even though her root was short, she was being harvested for a sweet snack.
Tom didn’t quite know what was happening until he felt the soil churn around his north-facing roots. Carrot had just enough time to say goodbye before she was uprooted and dumped into a wicker basket with the others.
For a few days Tomato was inconsolable. He indulged his melancholy, longing for his pretty carrot companion, the root he loved. But as the sun arced higher in the sky, his tall indeterminate vines sprawled, and one by one his fruit grew heavy and irresistibly red. Tom basked in the attention and admiration, forgetting his teenage heartbreak. There was no lack of water, no blossom-end rot, no wilts, no hornworms. All in all, Tom had a good season.
Read more about companion planting
“Companion Planting” rules as presented in popular books that anthropomorphize plants are vague and, in many cases, unsupported by science. For a critical overview of the topic, read Linda Chalker-Scotts’s The Myth of Companion Plantings. https://s3.wp.wsu.edu/uploads/sites/403/2015/03/companion-plantings.pdf . According to Chalker-Scott: “Pseudoscientific, mythological and occult applications of “companion plantings” are not scientific and will damage your credibility as a professional.”
Concepts that are supported by research include:
intercropping and polyculture: These are terms used to describe agricultural production methods using mutually beneficial species. The University of Vermont’s Food Systems Blog provides an interesting overview: https://learn.uvm.edu/foodsystemsblog/2014/01/09/controlling-pests-with-plants-the-power-of-intercropping/
plant associations / plant communities: In the fields of Ecology and Biology, these terms are used to describe species that: share a common environment; and interact with each other, animal populations, and the physical environment. https://www.dcnr.pa.gov/Conservation/WildPlants/PlantCommunities/Pages/default.aspx
trap crops (although some argue this practice is not really an “association”): This term describes the practice of adding plant species as decoys for pests https://ipm.cahnr.uconn.edu/perimeter-trap-cropping-works/
This tongue-in-cheek article was originally published in the April 2022 issue of Cross Pollination, the newsletter of the Halton Region Master Gardeners.
Does your love of gardening come with strong opinions, ideas that sometimes bolt from the brain and barge headlong into the world? When thoughts and convictions grow mouths and legs, do be wary—it could be a case of gardening activism! There is no cure but, with care, activism is a manageable condition. In fact, most activists lead healthy, productive, and meaningful lives.
Even if you’re not showing symptoms, take this handy quiz to see where you’re at on the activist spectrum. Don’t be surprised if you need to sit down with a cup of tea or a knitting basket. Or you may need to make a call, send a few emails, rattle some chains…
- You’ve guerrilla gardened an abandoned planter, a back alley, a boulevard, a hellstrip, a crack in the sidewalk.
- You’ve participated in a garden rescue.
- You get cranky when gardeners express love for their ditch lilies, vinca, goutweed, and lily of the valley. Rose of Sharon too, sometimes.
- You grow plants because everyone needs more great plants and everyone loves to find plants on their doorstep.
- You’ve quit a Facebook group because members keep gushing over “certain” plants.
- You argue with city gardening staff about how they should “get out of the 1800s”.
- You’re constantly doing imaginary makeovers on other people’s gardens, replacing all the exotics and invasives with “better” plants.
- Your front yard is turfgrass free. Give yourself a bonus point if you have a sign explaining why it looks that way.
- You handle a lot of seeds. You save, trade, give away, and mail them to strangers.
- You talk a lot about why we should not be doing the things we used to do.
- You’re always telling people where they can get native plants.
- You can’t go for a walk with friends without providing fascinating educational commentary on wayside plants.
- You explain Ecozones when someone asks about climate zones.
- You tell wildly hilarious jokes about “blue dawn.”
- You read and recommend gardening books with “revolution”, “manifesto” or “defiant” in the title.
What’s Your Score?
What’s your score? Are you an activist?
11 to 15: Hey Che, you’re a garden activist!
7 to 10: You’ve tried it and liked it…
6 to 9: You’re in the activist ecoregion but not the activist zone
0 to 5: You’re not an activist. But watch out—no one is fully immune!
Today (Aprl 10, 2022) I did a kitchen experiment to see if I could use our Instant Pot to sterilize triple mix.The reason for the desire to heat-treat the mix is the risk of Jumping Worms (Amynthas ssp.) an invasive species that has recently been reported in my city of Hamilton (Ontario Canada). Although the worms do not survive our winters (most die with the first freeze in autumn) the egg cases / cocoons survive very cold winters (to -35C). Any bagged “soil” product that contains compost or “black earth” is a potential source of jumping worm eggs. Research at the University of Wisconsin Arboretum showed that eggs are killed after three days at only 40C (104F). But, given that we won’t have temperatures hot enough to solarize anything until June or July, I decided to try heating my favourite triple mix indoors with an Instant Pot.
I expected the process would be safe, since Instant Pots are designed to be left on for hours at a time. In fact, the “slow cook” function allows a maximum of 20 hours continuous operation. The electricity used would be low (compared to the cost of running a gas stove or barbecue.) As well, the Instant Pot has a tight-fitting lid which would mitigate any odour.
I used a 7-litre DUO Instant Pot and filled it nearly to the top with CIL/Premier Triple Mix. This is my regular brand and I have alway appreciated it’s consistency and quality. I did try contacting the company’s customer service about how, or if, they mitigated the risk of jumping worm cocoons in the compost portion of their bagged products. I received a cut-and-paste replay (“our products are not know vectors etc etc”) which was not reassuring.
I used the Instant Pot’s “slow cook” function, on the “more” (high) setting. The lid was latched and set to “venting.” I checked the temperature (with a digital meat thermometer) at the bottom and top after 90 minutes and again after 5.5 hours. Here are the results:
90 minutes, temperature near bottom: 190F
90 minutes, temperature near top: 104F
1.5 hours, temperature near bottom: 194F
1.5 hours, temperature near top: 170F
Did it scorch or smell bad? No. In fact, the odour was earthy, and not unpleasant. Perhaps this is because I stored the bag outside all winter, but I really don’t know. Others have reported on the stink associated with sterilizing garden soil in a home oven, so I was surprised.
So, let’s look at the temperature results. Sterilization happens at 180F (enough to kill bacteria and other micro-organisms) and I expect it would kill jumping worm eggs as well. The research at U of Wisconsin showed that eggs were killed after three days at only 104F. I will try to find out if a short time at at 180F is enough to kill them.
The thermometer readings at 5.5 hours showed that the mix at the top (an inch or so down) reached only 170F. I continued heating the mix and, even after an additional hour, the top portion stayed at 170F. So, to be sure that the entire contents got to at least 180, some stirring would be necessary. If the Instant Pot had a cook function hotter than “slow-cook” but not as hot as “saute”, I could possibly increase the temperature to acheive sterilization at the top. Pressure cook is not an option since it requires liquid and the soil particles would clog the vent.
I expect that the mix reached the maximum temperatures (~190F on bottom / 170 on top) before I checked the temperature at 5.5 hours. In subsequent batches I’ll test at 30-minute intervals to see if I can reduce the time required per batch.
For now, though, I’m posting this to give my experiment an online home. This post will be updated as I learn more.
It’s about time, place—and data.
by Beverley Wagar, Halton Master Gardener
(This article was originally published on April 8, 2022, on the blog of the Halton Region Master Gardeners)
The end of March taught us, yet again, that climate change has turned the words “normal weather” into a quaint reminder of the good-ol-days—before CO2 levels began their steep rise, before we started wanting a second opinion on how soon to put the tomato seedlings outside. But now, with the weather weirdness getting weirder, do the “normal” temperature patterns of the past have any relevance to the present?
Yes—sort of. With weather extremes growing more extreme and occurring more often, the act of averaging the highs and lows does not convey a true picture of the chaos. But averages are still the best tool we’ve got for understanding how fast our planet is warming. How long they remain helpful for gardeners is another question.
“Climate normals provide a baseline to compare yesterday’s weather and tomorrow’s forecast to a standard for each location and time of year,” says Mike Palecki, project manager for the US National Oceanic and Atmospheric Administration (NOAA). Weather averages (“normals”) are available on various time scales: yearly, monthly, daily and even hourly. They are useful to energy companies, transportation schedulers, vacationers, and anyone who plans their activities in coming weeks or months based on what the weather is likely to do. Of course that includes farmers and gardeners.
We gardeners need to have a good understanding of the concept of temperature averages because that’s the way our springtime planning and planting protocols continue to be done. Understanding the meaning of “average last frost” allows us to interpret and understand the increasingly conflicting advice available to gardeners throughout the internet-connected world.
“Last frost” calculations start at the weather station. Environment and Climate Change Canada (ECCC) collects data from 1,735 weather reporting stations throughout the country. Some of these stations have been recording weather data for more than a century. Hamilton began reporting daily weather information in 1866; Toronto started in 1895. The Hamilton / Halton area has ten stations for which normals are calculated:
- Burlington TS (near QEW and 403)
- Hamilton Airport (Mount Hope)
- Hamilton RBG (Southwest Burlington)
- Middleport (near Caledonia)
- Oakville (Joshua’s Creek Trail)
- Vineland (near Grimsby)
Using Hamilton RBG data for our example, the average last-frost date (calculated by ECCC) is April 21.
Average last frost
But what exactly does “last-frost date” mean? (The phrase is more accurately “last 0-degree day” but more on that later.) To really understand the concepts of average and probability, we must tiptoe into the field of Mathematics.
Imagine a big spreadsheet that lists the lowest temperatue on every day between March and June, for the period between 1959 (when the RBG began recording weather data) and 2010. Now, highlight all the days it went below zero. Now, within these below-zero dates, for each year, find the one that occurs latest in the spring. Some will be in April and some in May. Now find the arithmetic mean (the “average”) of these last-frost dates. Et voila! April 21!
So, is this a safe date for a gardener to plant out? That depends on the amount of risk we’re willing to take. Remember that the concept of “average” means half of the last-frost days were before April 21—and half were after. Statistically speaking, it’s not quite correct to say there’s a 50-50 chance of frost on April 21, but you get the drift. And it may be a snow drift, so the wise gardener will wait for the risk to decrease.
How quickly does the risk increase or decrease before and after April 21? Analysts at the ECCC have calculated risk levels by plotting last-frost dates on a graph and determining the probability of frost on a given date. Looking again at the data from the RBG weather station, here are the probabilities that the last temperature in spring of 0°C or lower happens on or after indicated dates.
May 15: 10%
May 8: 25%
May 3: 33%
April 27: 50%
April 22: 66%
April 20: 75%
April 14: 90%
A couple of things jump out. First, why did they stop at 10%? On what date is there zero probability of freezing? We’ll look into this later.
And second: why is there a six-day discrepancy between the 50% probability date (April 27) and the average last frost date (April 21)? According to ECCC Senior Climatologist David Phillips, it’s due to how the statistics are calculated. It could also be related to the dataset used; it’s not clear whether the probability numbers were derived from normals (30 years) or all the data available from the RBG (51 years.)
When is there zero risk of zero?
So when is there absolutely no risk of freezing in the spring? On what date has the temperature never gone below zero in Hamilton? The answer is: May 31. This date was obtained not from ECCC but from WeatherSpark, a software company that makes interactive weather maps. Their calculation of “growing season” uses data from the Hamilton International Airport from 1995 through 2021. Yes it’s apples-to-oranges, but from a gardener’s perspective, it’ll do.
Unfortunately, math is not the ultimate crystal ball and air temperature is not the only predictor of whether your seedlings will survive outdoors overnight in mid-May. Remember that your garden is a unique microclimate. Cold air is heavier than warm air—it tends to sink into valleys. So frosts usually come first in valleys while hillsides can remain frost-free.
As well, your property’s microclimate is influenced by the amount and type of hardscape you have. Pavement, stone, and buildings collect heat during the day and slowly release it at night, warming the surrounding area. Swimming pools and ponds also create a buffering effect. For an in-depth look at microlimates, visit https://pss.uvm.edu/ppp/articles/frosts.html
Using a thermometer that measures temperature changes over time (sometimes called a temperature data logger) you can compare the actual overnight lows in your garden to the predicted lows. Of course you may not want to go full nerd on this stuff; simply observing your garden’s microclimate and general variance, either colder or warmer, from the forecast will help you know whether to schlep your seedlings indoors or to simply throw a sheet over them. (To learn more about frost damage, check out OMAFRA’s excellent page on the effects of extreme temperatures on tomato and pepper plants.)
Frost vs. freeze
Just because the thermometer stays above zero does not mean our plants are safe. Understanding the difference between “frost” and “freeze” helps us understand why the TV weatherperson gives stern frost warnings even though the temperature is not expected to dip below zero.
Frost is the white stuff on the ground. Freeze is the air temperature dropping below freezing. Sometimes we get frost when the temperatures are above freezing and we often have a freeze without frost. It all has to do with the dew point—the temperature at which water vapour in the air condenses on the ground and other surfaces (our plants!) as dew. If the dew point point is below zero, the water vapour condenses as ice, freezing as frost. The more moisture in the air (humidity) the higher the dew point. This explains why frost will happen on a dry, crisp night even if the temperature remains above freezing. For a more detailed explanation, here is an article by meteorologist Jeff Haby helping his peers educate the public about dew point: https://www.theweatherprediction.com/habyhints/190/
Shorter short-term forecasts
It’s evident that predicting the arrival of damaging cold can be tricky. So we might want to fall back on that old stalwart: the short term forecast. Surely we can rely on the Weather Channel, AccuWeather, TV Networks, or even the crowd-sourced Weather Underground to give us accurate predictions.
Actually, we can’t. By now we’re all aware that climate change is making things more unpredictable: hotter hots, colder colds, bigger storms, longer droughts, faster changes. But now, scientists have actually measured the extent of this unpredictability.
A November 2021 Stanford University study shows “rising temperatures may intensify the unpredictability of weather in Earth’s midlatitudes.” Lead author atmospheric scientist Aditi Sheshadri states: “Errors propagate through weather models faster as temperatures rise, and there don’t appear to be any temperature thresholds where the trend shifts.”
But let’s not backspace on all the algorithms. According to Alannah Campbell, a meteorologist with Instant Weather Ontario, “We can still predict weather on a short term basis, but weather and climate models can struggle with extreme events, making forecasting difficult.” She adds, “There are some models that do better with extremes than others and model developers are constantly trying to upgrade.” The NOAA has upgraded it global weather model, but Canada has not.
Time for the Ouija board?
Not yet! Science, although its power to predict weather is diminishing, is still the best tool we’ve got. Temperature predictions useful to gardeners, whether based on the data of historical norms or the skill of meteorologists, come with caveats based on our understanding of not only climate change and microclimates but also basic Math and Geography. We can make informed decisions that result in a tomato harvest. It might not be the earliest in the neighbourhood but, year over year, it will likely be the most reliable.
Canada is getting set to release new data on climate normals
Every decade Environment and Climate Change Canada (ECCC) re-calculates normals for the previous 30 years. Current (April 2022) normals are derived from the 30-year period between 1981 and 2010. A quick bit of mental math tells us we’re due for an update. The USA completed its update (see graphic below) in May of 2021 but ours is still in progress (as of April 8, 2022.)
David Phillips, Senior Climatologist at the ECCC, reassures us that the new normals data will be released in the summer of 2022, for the period from 1991 to 2021. Phillips is “anxious to see how the updated set of data, which will include the warm decade 2011 to 2020, will change the normals.”
As gardeners we can expect the average last-frost dates and the probability charts to shift. As well, there will likely be changes to Canada’s Plant Hardiness Zone Maps. And, of course, we’ll need to adjust our expectations for the 2023 gardening season.
by Bev Wagar
Knotweed’s ruthlessness calls for a special kind of response from Hort Court.
I wrote “Team Work” in early 2022, after a long break from the Hort Court series. No longer constrained by word counts (The Point is now digital only and I no longer contribute a gardening column), this one is much longer than the first six short pieces.
Rumours spread quickly in open meadows and Frankie the mole had heard enough of them to know when to stop chomping and take notice. Even with his tiny ears he could hear the fear in Windy’s voice when she hinted that Japanese Knotweed had been spotted by the creek. Frankie’s pal Ernie the vole, tunneling nearby, also popped up his head to listen.
“Windy’s just trying to keep everyone calm” said Ernie.
“And I thank her for that. After that close call in May, the last thing we need around here is panic.”
The two decided to head up to the courtyard and share the news with the garden folk. Hort Court had just adjourned and everyone was ready for lunch. The morning case had been difficult—Cup Plant and his seeds again—but Prosecutor listened carefully to the tiny harbingers. Ernie and Frankie were well known for their keen ability to detect the faintest of scents. If Knotweed had indeed come aground near the creek, the meadow and the garden were in serious trouble.
“It was a very faint rumour,” said Frankie. “Knotweed might still be a twig. We should act now before he puts down roots.”
So Prosecutor called all the garden plants to a meeting the next day. Meadow dwellers were also welcome, but only if they could put aside their feuds and quarrels with the garden varieties and share the courtyard peacefully.
In the morning, right at dawn, Prosecutor sent scouts down to the creek to see if the rumours were true. A pair of woodland sunflowers had volunteered for the job. Sisters Heelie and Anthus were tall, fast, diligent, and always smiling. Prosecutor could count on them to return with reliable reports. True to their word, the sunny sisters returned from their mission even before the dew had dried off in the courtyard. Had the terrible Knotweed come ashore? He was known for stealth on the waterways, taking advantage of storms and floods to send roots and shoots downstream where they could come ashore and start a new colony. But with high water and a fast current, Knotweed might have lost his rooting.
“Well?” said Prosecutor? “What did your big brown eyes see down there?”
Heelie, tired from the long run back from the stream, pushed aside her drooping golden petals and announced the bad news.
“It’s true. Knotweed has landed and he’s already put roots down. We had a brief conversation, if you can call it that. I’m afraid we’re all in mortal danger.”
With the big meeting about to start, details would have to wait. Most of the garden dwellers had already arranged themselves on the courtyard benches, silent and curious as the meadow folk drifted in through the back gate and stood nervously against the stone wall. They’d been taught to mistrust these exotics and cultivated varieties.
Prosecutor stood up and cleared his throat.
“We meet today at Hort Court in the shadow of a grave threat, one that affects us all. We have reliable reports of a Knotweed colony by the creek.”
Ernie and Frankie were the first to react, but their squeaks were quickly drowned out by gasps and groans from the crowd. Sunflower drooped even further. Several Nicotiana unintentionally released VOCs but, despite attracting a few braconid wasps to the courtyard, not an anther moved. Prosecutor continued.
“Knotweed has been found guilty in every courtyard this side of the lake. He’s invaded every garden he’s touched. No sheet mulch can stop him, no jail can contain his roots. His roots and stems break off and drift down our creeks and rivers. Tiny pieces, no bigger than a PawPaw seed, come ashore, take root, and grow fast. For those of you who’ve never seen Knotweed, he’s as tall as Panicum and his roots are just as deep. He’s mean, strong, and he won’t share his space with anyone.”
Switchgrass, unused to being called by his formal name, blushed from his spot in the back row. He’d only recently been invited into the garden and was still adjusting to his role as natural heir to Karl Foerster, who had stomped off in a spat about traditional values.
Prosecutor continued, his voice deliberately calm, aware of the tension that could ignite old rivalries.
“As you know, none of us is really equipped to keep Knotweed in check. Ever since he arrived in this land he’s been confounding our efforts. We need new ideas.”
Even the crickets were silent.
Beaver, who was fidgetting just outside the courtyard gate, finally spoke up.
“This Knotweed is a dangerous criminal. He’s out to wreck the pond and the stream too, unless we can stop him. I’m worried about my family. We just won’t survive once Knotweed takes over.”
Everyone nodded. Seasons ago, beyond anyone’s memory, Beaver and his kin had built the dam that created the pond. It was a huge attraction for birds and fish, not to mention the insects, amphibians, and mammals.
“I took a nibble of Knotweed this morning when he wasn’t looking” Beaver continued. “Didn’t much like the taste, and he hurt my teeth. But I think me and the missus could chomp him down to the ground, if we got to him soon. Maybe Spicebush could help us get rid of the taste.”
“Could you do it more than once? Maybe every few days?” asked Prosecutor. “Knotweed spreads faster than any scoundrel we’ve put put on trial—even Vinca. We would need to keep at him, not let him see the light of day. He’s a plant after all. Without leaves, he’s only got what’s in the root cellar and those supplies can’t last forever.”
The roots are the main problem,” said Beaver. “I can dig, but not that deep.”
“I can help!” All heads turned in the direction of the tiny voice. It was Ernie, standing tall and puffing out his chest ever so slightly. “I’m just a little vole with bad eyesight but I can eat pretty much any root in my path.”
“I’m in, too!” cried Frankie the mole. “I can dig way deeper than Ernie. I’ll dig, and Ernie can eat.”
The courtyard erupted in cheers and petal showers as the new rodent-mammal team high-fived one another. It wasn’t a solution—yet—but there was was cause for hope.
“Thank you all,” said Prosecutor. “Beaver, can you start today? And Ernie and Frankie, can you get in there as soon as Beaver is done? Our only chance is to get Knotweed while he’s small.”
All three nodded assent. As Prosecutor adjourned the meeting and everyone headed for the courtyard gates, Heelie and Anthus took the trio aside and offered some advice.
“Be careful, fellas” said Heelie. “That Knotweed is a fast talker. Really slick. When we were down there this morning, he started harping on about how much the bees loved his flowers, how delicious his shoots are in the spring, how it wasn’t his fault that he ended up in this part of the world, and how he’s not all that bad ‘cause he doesn’t spread by seed like Buckthorn and Honeysuckle. He even tried to tell us he was—how did he put it—stabilizing the stream bank.”
They snorted in unison. These were blustery exaggerations, weasel-words, and outright lies. Knotweed had mastered them all.
“What did you and Anthus say to that?” asked Beaver.
“Nothing. We just turned around and let the sun shine on our faces” the sunflower replied. “I raised my leaves and thought about this wonderful meadow and the beautiful garden up the hill, and how well this place works even if some plants misbehave and land in hort court. I thought of Mama Nature.”
“I think I woulda dove into a burrow,” said Frankie.
“Me too,” replied Ernie.
“We’ll be okay,” Beaver said kindly. “But hey guys, let’s get going—we’ve got a lot to chew on. Knotweed might wear us down and, even if we can’t evict him, we’re gonna make him stay put.”
He laid down his tail and invited his new partners to climb aboard. Beaver’s waddling gait made it hard for Frankie and Ernie to stand, but the pair still managed to wave farewell to the sunflower sisters and the hundreds of garden plants now cheering from the courtyard. The ones in bloom had arranged themselves into a bright garland that even Frankie could see. And, to everyone’s surprise, shy little Iris joined in, waving her blue flag, leading the valiant trio through the meadow grasses to the stream.
Photos below are Campanulastrum americana / Tall Bellflower, a Carolinian native listed as “common” in Hamilton (Ontario) area in Michael Oldham’s ‘List of the Vascular Plants of Ontario’s Carolinian Zone (Ecoregion 7E)’ (link opens in new tab) . Formerly known as Campanula americana and recently assigned its own genus Campanulastrum, this is an unusual bellflower, growing to 6′ tall (5′ in my garden) and preferring shade.
It’s a biennial that forms a rosette in the first season and then sends up a tall flowering stem the next summer. If you collect seeds and plant seedlings two years in a row (and also allow plants to re-seed) you’ll have these beauties every year. Take photos and make notes on the location so you don’t weed out your bellflower seedlings in the spring.
In my garden (Hamilton Ontario, ecodistrict 7E-3) Campanulastrum americana blooms in mid-July. I allow plants to re-seed next to a south-facing wooden fence shaded by asters, goldenrod, and a Chionanthus virginicus / White Fringetree. I expect the blooms to become darker blue as the Fringetree matures and the area becomes more shaded.
Comparing my photos to those on the excellent plant database at Texas A&M’s Lady Bird Johnson Wildflower Centre, (opens in new tab) I’m confident that this is our beautiful native Tall Bellflower. Last year some bellflowers came up in another part of my garden, in an area that’s I’d grown this one in the past. These turned out to be the dreaded C. rapunculoides. The young plants, thankfully, were easy to remove.
If you’re confronting this invasive, I feel your pain. But it IS possible to remove an infestation if you recognize your target and act quickly. Be sure to look for the “parsnip” taproot, which grows from the rhizomatous root system starting anywhere from 4 to 12″ underground, depending on the soil texture and moisture availablilty.
This graphic shows the telltale “parsnip” taproot of Campanula rapunculoides.
Be sure to remove every trace of rhizome as well as the taproot. This plant will regrow from pieces left behind.
Discard–do not compost.
The following photos will serve as a reminder to me to NOT ASSUME anything– and to keep better records. The original seed for these came from J.L. Hudson in California, more than a decade ago. I’m very glad to still have these beauties, despite last year’s shocking (terrifying?) experience.
I will definitely save seeds from these plants, but anyone who is given seeds is reminded of the responsibility to trust your source and your ID, especially when a gorgeous native plant may resemble an invasive thug.