How to Prevent Crabgrass

Push a soil thermometer 2 inches into the ground in a sunny area of your lawn. Check daily starting in early April (Central Plains) or late April (Upper Midwest). You're watching for 55 degrees held for three or more consecutive days. Air temperature is unreliable because soil warms more slowly.

Granular pre-emergents with prodiamine (Barricade) or dithiopyr (Dimension) provide the longest control window, typically 3 to 4 months. Dithiopyr has a slight advantage because it can also stop very young crabgrass that has just germinated. Read the label for your specific grass type because some pre-emergents damage certain turf varieties.

Follow the label rate exactly. For most granular products, this is 3 to 4 pounds per 1,000 square feet. Use a broadcast spreader for even coverage. Apply when the lawn is dry so granules fall through to the soil surface rather than sticking to wet grass blades.

Pre-emergent must reach the soil surface to form the chemical barrier that stops germination. Water in with half an inch of irrigation or time your application before a rain event. Without watering in, the product sits on top of the grass and degrades in sunlight before it can work.

In areas with heavy crabgrass pressure, split the total annual rate into two applications: the first at the normal timing and a second 6 to 8 weeks later. This extends the barrier through the entire germination season. Do not exceed the total annual label rate when splitting.