Each year, we struggle to keep the weeds out of the garden and lawn. Oh sure, not too many show up in May, and the ones that do sprout are easily controlled with a hoe or a dandelion digger. However, human nature being as it is, we soon tire of weeding. When early summer rolls arrives, and the weeds are more plentiful and much larger than they were in May, we often wish that we had done something to prevent all these weeds.
There are several effective weed control strategies – one of them is to apply a preemergence herbicide. This material is effective against weeds that you haven’t even seen yet; they haven’t emerged from the soil. The way this works is the herbicide is applied to the lawn or garden as the soil begins to warm. Because the roots start to grow first, they absorb the herbicide, and the plant is killed before it even comes out of the ground. Most annual weeds (crabgrass, goosegrass, foxtail) will germinate when the soil temperature reaches (and stays there for several days) 55-60 degrees. You can check for soil temperature by inserting an automobile air conditioning thermometer about a half inch into the soil. Every gardener should have an automobile air conditioning thermometer – they’re cheap and easy to obtain. You can also get an actual garden soil thermometer at most full service garden centers.
For the lawn, apply pendimethalin or prodiamine according to label directions. Some products recommend a second application around Memorial Day (six weeks later) to keep the level of herbicide in the soil high enough to be effective. This is recommended if the product has a short residual, or if the lawn has had lots of annual weeds in past years. Be sure to water the lawn after application.
For the garden, wait until all the veggies and annual flowers that will be started from seed are up and growing. Then apply trifluralin or corn gluten meal between the rows, and around plants. In the perennial flower garden, clean off all dead foliage from last year, then sprinkle the herbicide around the plants. In most cases, the plants will become larger as the season progresses, and the leaf canopy from the plants will shade the soil and reduce the germination of weeds. However, until that happens, you need other measures – hoeing and herbicides. Mulches can also be used after the soil warms adequately, usually in mid-May.