weeds/grass among flowers

Asked January 13, 2020, 4:21 PM EST

what can I use as a grass/weed preventer in my flower beds

Allegany County Maryland

1 Response

If specific kinds of weeds tend to be a problem, identifying them can result in a more effective, targeted approach. Some common weed photographs by season are pictured here: https://extension.umd.edu/hgic/topics/spring-weeds
For general weed control, there are several methods that should overlap to minimize pesticide use. Cultural control - making the area less hospitable to weeds - is the best place to start. In this case, it would mean using either a bark mulch or living mulch (such as perennial or evergreen groundcovers) to prevent weed seeds from both landing on soil that they can root into and to prevent existing weed seeds in the soil from getting enough light to germinate. In addition, by having healthy, vigorous plantings, their root systems will help out-compete any weeds that try to grow there by using the available water and nutrients before the weeds have access to it. Their leaves will also shade more of the ground, lessening the light available to the weeds.

Physical control - hand pulling or cutting-down - is another good way. Cutting is better than the pulling because it doesn't disturb the soil, which always carries the risk of bringing dormant weed seeds up to where they'll receive enough light and water to germinate. However, cutting is better for annual weeds and pulling would be better for perennial weeds.

Chemical control is the last resort but may be the most effective against stubborn, vigorous, perennial weeds. Herbicides are lumped into four overlapping categories. Broad-spectrum are fairly indiscriminate in that they have the potential to damage most plants. Selective are more targeted, usually for either grassy weeds (and some chemicals don't discriminate between lawn grasses and weedy grasses) or broadleaf weeds, as they metabolize differently. Pre-emergent herbicides target germinating seeds and are best applied just before germination time. Crabgrass, for instance, germinates around the same time Forsythia blooms, as both need about the same amount of warming time in spring to trigger growth. "Winter annual" weeds germinate in fall as they grow in cool weather; "summer annual" weeds germinate in spring as the weather warms as they grow in warm weather. Therefore, depending on the types of weeds present, more than one treatment of pre-emergent may be needed. Read the package label, however, because they should not only list the weeds controlled but how long the treatment should last (or how long to go between treatments) because of slow-release formulations. Post-emergent weed products treat weeds that have already sprouted. Applied either as granules that stick to wet leaves or as sprays themselves, they either kill off all top growth (sufficient for annual weeds) or are absorbed by the leaves and transported to the roots. The latter are systemic herbicides, and are best - or required - for perennial weeds that store a lot of food reserves in their roots; killing only their top growth would only be a temporary solution.

There are too many products on the market to suggest something specific. Given the advice above, see if you can select something attuned to your weed population for best control. Products containing glyphosate, on the other hand, are broad-spectrum, meaning they will damage or kill anything the spray touches. Active ingredients will always be listed on the package label - usually on the front, at the bottom, in small print. Some, like glyphosate, are marketed under many different trade names but will always be called glyphosate in the ingredients list. Broad-spectrum herbicides would be the last resort given the risk of exposure to desirable garden plants but may be the best solution to spot-treat particularly troublesome weeds if you can target them carefully.