If you’re struggling with weed invasions in your vegetable garden, flower bed or lawn, you’re not alone. In fact, weeds are a problem for gardeners everywhere, reports the University of California Integrated Pest Management Program. While manual and cultural practices, such as tilling and appropriate fertilization and irrigation, can help control weeds, some gardeners opt to spray weed killer on their problem. If you go the chemical route of using herbicides, spraying them on your weeds at the right time can help maximize your success in the weed war. Much of it depends on the specific kind of weed killer you are using.
Gardeners commonly use pre-emergence herbicides in areas like an established lawn to help disrupt weed life cycles, especially when it comes to annual problems like summer weeds. Examples of common pre-emergence herbicides include dithiopyr and benefin, all which generally stop weed seeds from germinating. For the best results, gardeners should time the weed killer application to take place before weed seeds start to germinate, generally in the early spring. Gardeners often reapply the weed killer approximately eight weeks after the first spraying to help with exceptionally invasive weeds, such as crabgrass.
Post-emergence herbicides, such as the widely used glyphosate chemical, generally kill weeds upon contact by getting absorbed into the plant tissue. For optimal absorption, such weed killer works best when applied to new, young weeds. If a gardener is battling an established weed population, such as woody shrubs, better results may occur if the gardener cuts the weed down to the ground and waits for a few inches of new leaves and shoots to appear.
For the best results, most weed killers work best when the application of the herbicide occurs during several days of dry weather. Otherwise, rainwater can rinse the herbicide from the surfaces that you need to treat. Additionally, any residual effects of an herbicide will get diluted by the rain, sometimes to the point of inefficacy. Another weather-timing situation to factor in is wind, specifically when applying glyphosate or similar nonselective herbicides that kills all plants — including desirable vegetation, such as your flowers or vegetables. Windy conditions can create herbicide drift, distributing the chemicals onto other areas of your landscape and killing your desirable plants.
Additional Timing Considerations
Herbicide application must fit a gardener’s general landscaping timeline. For example, some herbicides kill weeds within days while others take a week or longer. Depending on where and why weeds need removal, herbicide application must take into account the other needs of the gardener. For example, if replanting must take place within a certain window due to temperature concerns, the weed killer must be applied early enough. Additionally, some herbicides have a residual effect and remain toxic to plants for months. Before choosing a weed killer, read its label to see how long it takes to work as well as how long it will linger in your landscape.