Should I Let the Turf Weeds Grow?
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With widespread concern about declining populations of bees, other pollinators and other beneficial insects, many gardeners are wondering how they can help stem the loss. Avoiding the use of insecticides and herbicides in the lawn has been suggested as a simple way for gardeners to help. The supposed benefits are reducing exposure of these insects to harmful chemicals, while also allowing weeds to flourish to provide foraging habitat.
As is often the case, the reality is a bit complicated and the answer isn’t completely clear. And while additional research is sorely needed on these questions, gardeners can be certain of two things:
- Insecticides, herbicides and other pesticides should be used judiciously. This means identifying the specific problem, considering other management options, doing spot treatments where practical and using no more than the recommended amount.
- Product instructions should be reviewed carefully and followed explicitly. Those instructions provide all the details needed to get the desired results while minimizing risk to people and the environment.
REDUCING TOXIC IMPACTS ON BENEFICIAL INSECTS
Regarding potential toxicity of the products, insecticides are by far the biggest concern. And by happy coincidence, there is rarely a need to use them in a home lawn. When a gardener does identify a legitimate need for an insecticide application to the lawn, the instructions will provide all the details needed to protect bees. But as a general rule, they should not be applied when those broadleaf weeds are blooming. And while the instructions typically do not specifically address other beneficial insects, the precautions mentioned to protect bees will generally be adequate.
The risk of direct harm from fungicide and herbicide applications is significantly lower, although some studies suggest the risk is not zero.
ALLOWING WEEDS TO FLOURISH
As noted above, allowing turf weeds to flourish has been suggested as a simple way to provide nectar sources for foraging pollinators in early spring. The weeds of interest are mostly cool season broadleaf weeds such as henbit, deadnettle, clover, chickweed and others. In this part of the world, they germinate over the winter and then begin to take off in late February or early March, usually in full bloom by the end of March and early April. This is, in fact, a time that many pollinators are becoming active and when few other flowers are blooming. Thus on the surface, it seems like a logical solution.
The specific practices to accomplish such a goal would include not mowing while the weeds are blooming, reducing or eliminating the use of broadleaf turf herbicides, or even purposefully seeding “weed” plants (especially clover) into the lawn.
Following these practices, however, will involve some tradeoffs, and there may be alternative practices that could be equally beneficial.
The first tradeoff is that allowing weeds to grow in the lawn will likely mean increased weed pressure in adjacent vegetable, flower, groundcover and shrub beds. Weed seeds will move into those beds by wind, runoff and other methods. Mowing with a discharge chute can propel weed seeds many feet into beds if care is not taken with the direction of discharge. Mulching mowers can mitigate this to some extent.
Secondly, it may be impractical to allow only “desirable” weeds to proliferate. Not all broadleaf weeds provide pollinator benefits, and some weeds could be unwelcome for other reasons. Lawn burweed, for example, produces prickly structures. Spot treatments with an appropriate herbicide could be used to eliminate patches of undesirable weeds, or individual plants could be removed by hand. Once treated, it would be best to replant bare areas with turf or clover to help prevent a reinfestation of the undesirable plants. However, where undesirable and desirable weeds are mixed together, selectively removing the former, either by hand or herbicide, would in many (most?) cases be impractical to impossible. These strategies would require close monitoring of the lawn as well as timely implementation.
AN ALTERNATIVE APPROACH THAT’S MAYBE JUST AS EFFECTIVE
It might seem as though having high quality turf and protecting beneficial insects would be mutually exclusive, i.e. you have to pick one or the other. But perhaps it’s possible to achieve both goals.
High quality turf, afterall, can be a very functional and attractive component of the landscape, providing play areas, walking paths, erosion control and more. And using recommended practices related to mowing height, fertilizer rates and timing, irrigation, etc. will help keep turf free of weeds, disease and insects while minimizing inputs.
Beneficial habitat can then be provided by planting the right trees, shrubs and flowers. Books have been written on the topic, but it basically boils down to this:
- Plant a variety of flowering trees, shrubs and flowers. Natives are great, but non-natives can help too.
- Select plants for each season. Aim to have a variety of things blooming throughout the growing season (spring to fall).
Deciding which approach to take is up to the individual gardener. But keep in mind that supporting beneficial insects is a bit more involved than simply letting the weeds grow.