By Beverley Wagar, 1000 Islands Master Gardeners
This article was inspired by Lorraine Johnson’s online chat on November 27th 2025, part of the ongoing “Ask a Master Gardener” webinar series hosted by the 1000 Islands Master Gardeners. For the zoom link, sign up for the TIMG newsletter (opens in new tab).
Say you’ve driven to the grocery store and all the good parking spots are taken. So you go around back, to the barely used lot that’s full of gaping cracks, heaved asphalt, and dried-up potholes. Allowing your inner botanist to take charge for a moment, soon you’re outside looking at the plants growing in these places.
“Look at all these weeds!” you say to yourself. But are they really? Weeds are simply plants growing where they’re not wanted. “Weed” is an informal descriptive term with no technical meaning. There’s no official list, no “weed” category in plant taxonomy.
Botanists and ecologists are more likely to use ruderal to describe a plant with weedy behaviour. “Ruderal plant” has an objective meaning. Defined by their function in a disturbed site, ruderals include many species that show up and thrive in harsh, changing conditions, in soil that is often degraded or polluted. In general they are not picky about soil type or nutrient availability. They are first-on-the-scene, early-succession, disturbance-adapted plants. Colonists, in the botanical sense.
Ruderal roles in the landscape
“Ruderal” derives from the latin word ruder– (rudus) meaning “rubble”. Looking at an urban ruderal site you may not be reminded of Roman ruins, but you’d immediately see that the place was created by humans, who subsequently abandoned, forgot, or shunned it. Ruderal sites exist in rural areas as well—consider roadside ditches, abandoned fields and farmyards, old landfill sites and mines.
Landscape architect Elizabeth Burdick, looking at urban places, puts it plainly: “Without construction debris, demolition wreckage or abandoned sites, there would be no habitat for ruderal plants. Ruderals are a set of species which can outcompete others in poor conditions, but typically are themselves outcompeted in rich environments.”
Ruderal sites are often, but not always, created by human disturbance of the soil. Plowing, digging, mowing, burning, and tree-felling are common examples. In a broader sense, disturbance includes any occurrence that abruptly changes the original community of plants. Consider how tree throws, landslides, wildfires, and invasive species (jumping worms, for example) alter the soil and the plants it is able to support. Even the act of clearing turfgrass to create a new garden is a disturbance that exposes buried seeds to light and moisture, removes the temperature-buffering vegetation layer, creates conditions for erosion during rainfall, and (on the positive side) provides habitat for ground-dwelling bees.
Many ruderal plants are annuals or biennials. Putting energy into fast growth and copious seed production results in an abundance of progeny that leaves little room for competitors. Rapid turnover (a new generation each year) results in high genetic diversity and adaptability which improves an individual plant’s chances of surviving periods of stress long enough to set seed and ensure a new generation.
Ruderals tend to be wind-dispersed. Not only are their seeds carried far and fast across open landscapes but also they are not reliant on water or wildlife (such as birds) to move them to a new place. As well, they are often self-fertile, meaning that the stigma of one plant accepts pollen from the same plant. This ensures that even a single, isolated plant can produce seed, regardless of the presence of bees or other pollinators.
Healers and first-responders
Ruderals take hold in bare ground, dominating and holding space—but only temporarily. They comprise an ecological social safety net that works so well it’s eventually not needed. Selfless, tireless healers, they create the conditions for their own demise. They trap leaves, which break down to form the beginnings of topsoil to provide nutrients and water-holding capacity. Like all terrestrial plants, their roots grow and die back as conditions change. Dead roots become organic matter that decays, leaving channels for water and air that will, over time, provide habitat for soil-dwelling organisms, reduce compaction, hold moisture, and moderate the surface temperature. Root exudates are essential to material cycling, energy exchange, and information transfer between the belowground parts of plants and the soil. As the soil changes, it becomes more hospitable to species able to compete with ruderals, ones generally longer-lived and better suited to later successional stages.
Being first-on-the-scene plants, ruderals are nature’s first responders, the gritty paramedics of the plant world. Not only do they change the soil and, in many cases, buttress against invasive species, they also attract insects and birds wanting pollen, nectar, and seeds, especially if they’re native ruderals. Their presence can buy time for more complex, diverse, and shade-tolerant communities to establish. Some species are used in site remediation work because they are able to remove pollution and contaminants from the soil.
Native and exotic
While urban non-native ruderals, whether they blow in from the roadside or from nearby gardens, provide many of the restorative services described above, they contribute little to the ecosystems we need to protect and restore. These ecosystems support a robust food web that provides for native species, especially insects, that are experiencing alarming declines. It’s important to look past the butterfly on a chickory, blueweed, or dandelion and instead consider the evolutionary relationships crucial to the health of native insect and bird populations. Native plants, having evolved with native fauna over many thousands of years, are recognized as food. They’re “host” plants—ideal places for insects to lay eggs because the larvae can eat the leaves they were born on. This is why native ruderals are so important.
Look at any field guide to Ontario wildflowers and you’ll see a preponderance of non-native (“exotic”) species. It’s no wonder that novice gardeners often think a plant must be native because “it’s everywhere.” Native ruderals are less likely to show up in urban sites if they don’t already exist in nearby fields or woodlands. So what should the concerned urban gardener do to help native ruderals get established?
First, work to protect nearby native plant communities, especially forest remnants. Join a volunteer group that does invasive plant removal and plants natives, especially trees and shrubs. Second, if there are no native plant communities nearby, plant some—in your own garden or a community garden. But make sure they are regionally native, not rare or endangered, and ideally from a local wild population. Third, resist the urge to “help” by scattering seed from over-the-counter wildflower mixes, which tend to be heavy on non-native “pretties” and light on the ecological workhorses. Should you deadhead the exotic ruderals in the parking lot to make space for potential native ones? Only if you see native plants starting to make inroads on the same site. Consider collecting seeds from native plants growing close by, on a similarly disturbed site. These reference communities will show you what species are already adapted to local conditions.
Ruderals in the garden
Should we introduce these plants to our gardens? It depends on your site, goals, and available time. As you wait for your perennials and shrubs to mature, ruderals can serve as fillers for a season or two. If you leave bare soil, they will inevitably show up uninvited—and soon you’ll be orchestrating some kind of balance between your new guests and the ones you’re waiting on.
Remember that a ruderal is defined by its function, not its species name. A grey goldenrod (Solidago nemoralis) is ruderal in a neglected hellstrip. But put it in a garden and it’s an adaptable, tidy, keystone perennial. A common evening primrose wears the ruderal hat when it pops up in a recently cleared roadside ditch, but many native plant gardeners overlook its fecundity and embrace its tap-rooted, clay-busting, back-of-the border bee magnetism.
Here are some ruderals that may show up in a garden or a disturbed site near you. Eastern burnweed (Erechtites hieraciifolius) is an annual most likely to show up after a fire. Erigeron canadensis (syn. Conyza canadensis, better known as horseweed) along with its cousins the biennial Erigeron philadelphicus (common fleabane) and Erigeron annuus (annual fleabane), are likely to show up in disturbed urban sites but can be introduced to new garden beds, especially hellstrips and boulevards, as temporary cover. Clinopodium arkansanum (low calamint / wild savory) and Polanisia dodecandra (red-whiskered clammyweed) are ruderals for full sun and dry conditions, as is the unquestionably garden-worthy Rudbeckia hirta (black-eyed susan) and the aggressive but useful Achillea millefolium (common yarrow). There are two Ontario native avens (geum spp.) and two Ontario native false bindweeds (Calystegia spp) although you probably don’t want to deliberately introduce the bindweed. If your disturbed space mimics a forest edge you could introduce clearweed (Pilea pumila) or Clinopodium vulgare (wild basil, a perennial).
You may not want to deliberately introduce ruderal plants to your garden, but if they show up, do treat them with respect—or at least as a botanical curiosity worthy of further study. These “first encounters” are fascinating opportunities to grow your expertise. So before you yank, learn their names and their ecological function. And be open-minded when it comes to inconspicuous flowers—remember that ecological function includes more than just pollinator appeal.
Further Reading
(links open in new tabs)
“Ruderal Resilience” Christopher Lee Kennedy on Medium. A wide-ranging essay on ‘marginal landscapes’, their particular resilience to climate change, and how they might thrive in the Anthropocene.
Bio-Inspired Land Remediation (book introduction)
Ruderal Plant Diversity as a Driver for Urban Green Space Sustainability European research but still relevant
City of Weeds: Tracing the Origins of the Urban Ecological Imaginary from MIT press. Geographer and urbanist Matthew Gandy explores the fascinating history of spontaneous forms of urban nature.
Ruderal Heritage (book chapter) Another expansive look at the ruderal, for those interested in critical heritage studies. “The wider recognition of inevitable transformative change has been paralleled by the emergence of new theoretical approaches, which understand heritage as a socially-embedded, future-oriented process through which the past is brought into the present to shape novel environments and practices.”