Crabgrass is a very persistent, annual weed that germinates in May, goes to seed in August and gradually dies off during the early fall. Each plant can yield tens of thousands of seeds, which can lie dormant for several years before they germinate. Obtaining consistent control of this weed is one of the most important challenges we face in the spring.
Pre-emergent control products can effectively reduce crabgrass, but they will not eliminate it entirely. Properly applied, these products can last up to four months. Some factors limit the effectiveness of pre-emergent materials including weather, soil temperature and moisture content, turf density and the weed seed available.
To increase the effectiveness of the pre-emergent, rainfall or irrigation should occur within 20 days of application. This helps the pre-emergent to adsorb to soil particles that creates the barrier to help prevent crabgrass seeds from germinating. In the spring, natural rainfall is usually plentiful, but supplemental irrigation might be needed if there is an early extended dry period.
Once the product is in place, steps should be taken to minimize anything that might disturb the soil surface. Surface raking, mowing or sweeping the turf is fine, but if you de-thatch your lawn with a machine, you risk effecting the level of control down the road.
During July and August, warm and/or dry soil can contribute to pre-emergent control breaking down prematurely. This is why crabgrass can appear along drives, sidewalks and any thin/ bare areas of your lawn. To help minimize this, keep mowing height at 3-3½ “ and water deeply every 2-3 days between rainfalls. This keeps soil cooler and helps reduce the chance of break through, not to mention it is better for your lawn.
Post-emergent treatments are available to control crabgrass break through, but are only effective on actively growing weeds and cannot be applied to brown (dormant) turf caused by drought and/or heat stress.
Feel free to call us if you have any questions or would like to learn more about crabgrass.