Garden Calendar: Weeding out dandelions and henbit

Dandelions actually began growing last fall and will be troublesome this season.

Through the window I can see just a few yellow dandelion blooms dotted through the grass. Next week there will be more — in the flowerbeds and the vegetable garden and nearly every crack in the sidewalk.

While I think a few dandelions are okay, the hundreds of viable seeds produced by each bloom worry me. Additional concern comes from the delicate purple blossoms of henbit, which is quickly filling in where the dandelions are lacking.

The really bad news is that the henbit and dandelions actually started growing last fall. The other common cool-season weeds, including chickweed, deadnettle, bedstraw and several others, also sprouted about October.

Germination time is important because unwanted plants are easier to control when they are little. Putting on an additional layer of mulch in the flowerbeds last fall helped keep light from reaching the seeds. Fertilizing the fescue lawn in September to get it growing strong helped the grass outcompete at least some of the invading species.

A pre-emergent herbicide labeled for cool-season broadleaf weeds could have been a tool, too, but it is too late to apply it now. For effective control of henbit, chickweed, etc., applications should be made around mid-September.

Besides pulling these pesky weeds, what can be done now?

In the lawn, mowing frequently can help keep weeds in check. (Since weeds typically grow more quickly than turfgrass, a weedy lawn means mowing more often anyway.) In landscape beds or gardens, weeds can be cultivated under the soil surface. Weeds that are covered with mulch often re-emerge as a stronger plant.

Locations that are especially rampant with weeds can be covered with plastic to kill the undesirable plants by solarization. Simply cover the area, weight the corners of the plastic or pin with landscape staples, and leave the plastic on for a number of days. This method works best in full sun.

A post-emergence broadleaf herbicide is another option for cool-season weed control but should be used with caution. First, if you are planning to put down any additional grass seed, avoid using a broadleaf herbicide for four to six weeks prior. Once new grass emerges, it should be mature enough to mow at least three times before a broadleaf herbicide is applied.

Post-emergence herbicides can also contribute to stormwater pollution, so avoid applying products when rain is expected within 24 hours. Do not water the grass after application. Avoid applying post-emergence herbicides when temperatures exceed 85-90 degrees.

Warm-season broadleaf weeds are less common in both the lawn and garden and are usually easily controlled through good cultural and mechanical practices.

Unwanted grasses or grassy weeds are another story. The really problematic ones, like crabgrass and bermudagrass, are warm-season plants and will be problems in mid-summer when the cool-season lawn is struggling. Crabgrass seeds sprout about the time the redbud trees reach full bloom, so pre-emergent applications need to be applied prior to that time.

Post-emergence herbicides for grasses work in flowerbeds but often affect the desirable grasses in the lawn as well as the unwanted species. Again, thick turf will outcompete weeds. Solarization, mechanical removal or use of a nonselective herbicide may offer the best long-term control.

There are a few other options for spring weeds, at least. You could make a dandelion salad (bitter like arugula) or go into the dandelion wine business. You could also make bouquets for someone special. I now understand that my mother’s smiles over the arrangements of chickweed and henbit I used to make were because she had a few less weeds to pull.