How to approach problem weeds sustainably
If you are a gardener you are no stranger to weeds and weeding. In fact, it could be stated that the act of gardening is really just the battle to keep your yard populated with the plants that you have chosen, rather than those which grow all on their own. In any Lethbridge yard, you’ll find weeds like elm, green ash, sunflower, native fescues, canola, and even desirable annuals that have self-sown, sprouting up everywhere in the spring when the soil warms up. These “weeds” are just a group of locally grown plants that the gardener doesn’t want taking over their garden spaces and they are likely as unwanted as any weed listed on the Alberta Invasive Plants list. This article discusses the difference between annual and perennial weeds and sustainable techniques to stop them and/or keep them from taking over your managed outdoor spaces.
Annual Weeds
As discussed in our last blog, annuals are plants that complete their life cycle in one growing season and do not re-emerge from the root the following year. When it comes to noxious weeds, annuals tend to erupt from last year’s seed at cooler temperatures early in the spring, mature quickly, and set huge amounts of seed that gets dispersed by wind and organisms that forage them (or simply rub against them). What makes them even more difficult to deal with is that they can also germinate at higher temperatures and can be drought-tolerant (or, alternatively, adapted to wet areas), which means they can continue to grow new plants and set new seed throughout the season. The type of annual weeds you see in your yard depends on where you live and how you manage your landscape.
For example, the three top annual weeds that I battle with in my area (outside of the aforementioned desirable plants) are downy brome, kochia, and wild buckwheat. The first two plague the back laneway in the hot, dry, compacted environment and the wild buckwheat hides in my perennial beds, winding its string-like vine around growing plants. All three produce copious amounts of seed and all three require removal or cutting to the crown at the leaf stage to avoid seed set.
The best sustainable management techniques for annual weeds involve the following: One, mowing/weedwhipping to the crown while the weed is early in leaf (before flowering), then raking the debris and putting it in your green bin ONLY IF THERE IS NO FLOWER BUDS/SEED/ROOT IN THE DEBRIS (if you are unsure, bag it, tie the bag, and toss it in the black bin: downy brome is so fast to maturity you likely won’t recognise it until it’s seeding). Two, pulling the weeds: many varieties of annual weeds are easy to pull (note that wild buckwheat will tighten around your plants if you pull it from the bottom and denude them of leaves, so you have to be careful to unwind it). These need to be bagged and tied securely and put in your black bin as annual weeds can set seed with their root attached and if they have formed a flower some can even set seed with just the energy from the leaf and stalk.
Perennial Weeds
Invasive weeds of this type are far more nefarious and difficult to manage as many have hugely extensive root systems. This not only starves the soil of moisture and out-competes other plants but also makes the weed very difficult to remove. Often, if only a small piece of root is left behind, the plant will survive. Three of the most difficult perennials I deal with in my Lethbridge landscape are Canada thistle, field bindweed, and creeping bellflower. The size of the infestations relates directly to the amount of time and resources required to manage them.
Sustainable management of these weeds requires patience and vigilance: there is no quick solution for infestations of this type. First, if you are purchasing a new property, have a close look at the landscape and ask questions about how it has been managed. Large infestations of perennial weeds can be very costly and frustrating to a new homeowner. Canada thistle is well known to everyone but field bindweed is often found in hot, exposed, lawns and can only be seen easily if it is flowering. Similarly, creeping bellflower can exist in any environment and will also hide in lawns. Broadleaf herbicide can hide these problems from potential purchasers and there is no legal duty for the seller to report on weed infestations. Note that all three of these perennials are resistant to herbicides due to their extensive root systems but an application of broadleaf herbicide before the house goes up for sale can make the exposed leaf disappear for a few weeks.
Second, if you have a large infestation in a level area, you may consider sheet mulching as a sustainable management technique. This might involve covering the area with cardboard and mulch, but that is unlikely to deter robust perennial weeds for long. The proper way to sheet mulch to smother a weed infestation is to low-mow the entire area to the crown of the plant and water the area heavily, cover with several inches of manure or unfinished compost (to create an environment where breakdown, rather than growth, is occurring), cover the manure with several inches of screened topsoil, heavily cover that with well-overlapped cardboard, then six to twelve inches of wood mulch. The cardboard and mulch will work to suppress top growth of weeds while they smother the undergrowth. Note that the area will be high but will deflate as the materials break down. It needs to be watered weekly through the growing season and WEEDED VIGOROUSLY. You shouldn’t plant into this for at least two full summers. This is a technique that is very intensive but will ultimately build the soil for new planting as it kills the weeds.
Third, another technique for large infestation is complete replacement: contracting a landscape company to remove the soil and plants in the area, find the leftover roots, and then replace with good quality, screened topsoil and plant. This is obviously a very expensive option and will require continued efforts against weed re-emergence.
Fourth, if you have a small, localised infestation, dig it out and find the root then discard plant, root, and soil in a tightly-tied bag to your black bin (or take it to the Lethbridge Waste and Recycling center and let them know you have noxious weeds for disposal). Alternatively, for small amounts of weed growth in concrete or rock, try flooding the area with boiling water (note that this will kill any perennial it comes in contact with – be cautious).
Finally, continued vigilance is required for any perennial weeds: set aside time to pull out leaves and remove any flowers weekly. If you continue to do this you WILL eradicate the perennial infestation on your property, as the local plant will be unable to sustain its root system in your yard. From there, you maintain the boundary with the adjoining properties/laneways by weeding out anything that crosses it. I have eradicated horsetail and Japanese knotweed on my BC property (it took three years) and am two years into management of bindweed and bellflower here in Lethbridge. It IS possible. The kochia in the back alley? It comes back every year and requires weeding every year (but that is on ME: the area is unseen and rather neglected).
In closing, it is important to mention that any type of outdoor environment requires regular maintenance (even concrete). If you have a green space, you will certainly have weeds. Herbicides are a poor management technique for noxious and/or invasive weeds as many (if not most) varieties are resistant. More importantly, though, herbicides degrade the soil by destroying beneficial organisms, so the more susceptible the landscape becomes to weed infestations with repeated herbicide use. Therefore, herbicide is a poor management technique for any weed because it tends to create the soil conditions where weeds thrive. The best way to avoid excessive weed infestations is to have a healthy perennial environment (trees, shrubs, flowering plants, polyculture lawns/groundcovers) managed from the soil up. Regular spring applications of compost and fall applications of organic mulch keep beneficial insects and micro-organisms growing and working for you. Avoiding compaction and regular weeding/plant thinning keeps the soil aerated and fluffy, which houses beneficial soil microbes that break down nutrients for your chosen plants.
For further information on the weeds you are dealing with at home, see Environment Lethbridge’s Invasive Plants of Lethbridge and this great visual tool from the City of Edmonton.
