Crabgrass frenzy is beginning. Crabgrass is a summer weed that germinates when soil temperatures are 60 degrees for three to five days.

By Mark Evans
ANR Plant and Soil Science Extension Educator Purdue Extension Elkhart County

GOSHEN — Picking a specific date on the calendar for application of annual crabgrass preventer is not the best decision tool. Paying attention to soil temperature or growing degree days is a better indicator.

Mark Evans

For crabgrass, planting seeds in the top quarter to half-an-inch of soil while germinating at a temperature of 60 degrees is necessary for the seeding process during warm grass season. The chemical in the preventer, herbicide, needs roughly one week to 10 days for incorporation into the soil, if there is enough rainfall.

Areas along the south side of a structure, especially buildings made of brick or concrete, will keep warmer. For good control, apply preventer to these areas now. Lighter textured, sandy soils that drain well will warm-up faster than those with heavier clay content or more waterlogged soils.

On the morning of Monday, April 7, ice formed on the puddles despite a temperature in the lower 30s with an expected temperature in the mid 20s the next two evenings, with no recent temperatures in the Elkhart or Michiana area forecast to reach the mid 60s or higher through the end of the week.

Despite past research suggesting that early applications of crabgrass preventer can control through the entire season, last year there were several reports in the area of the products running out of steam before season’s end.

Factors like the dryness and warm weather appearing later in the summer and fall favored the warm season crabgrass, while it hindered the cool season turf grasses. Additionally, prevents products may have ran out of effectiveness, given it was November before the first freeze came seasonally.

Product applied prior to seed germination is critical to the prevention process, with no reason to feel worried you are too late in most landscaping cases.

Make sure that product is spread evenly according to the label. Keep an eye on the long-term forecast.

The weekend of Saturday, April 12, and Sunday, April 13, will likely be a great time for application or a few days thereafter. Application prior to a nice shower would be favorable as well, avoid products with nitrogen or other fertilizer in them as that can favor weed growth particularly in stressed lawns from last fall. Wait until this coming fall for nitrogen application.

To support cool season turf grasses in your lawn, mow at least a 3-inch height as mowing turf shorter favors weeds and warm season grasses like crabgrass.

For more information on products and considerations, check out Purdue’s AY-10 online.

Contact the Purdue Extension Elkhart County office at (574) 533-0554 for questions as well.