Crabgrass is an annual grass which can pose a problem in lawns and gardens in southern Ontario. Once crabgrass makes its home in your garden it is a very unpleasant and difficult weed to eliminate.

Crabgrass spreads by seeds produced and distributed in the soil from previous years. Seeds can live for up to 15 years in the soil, waiting for the opportunity to germinate when a bare patch of soil is exposed to sunlight. Each crabgrass plant can produce up to 150,000 of seeds. With this type of intensity and persistence it is easy to see that prevention is the best cure for crabgrass!

Crabgrass will begin to germinate when soil temperatures reach 60F (15C). This usually takes place in about mid-May and germination will continue throughout the spring and summer. Mother Nature supplies a helpful clue since crabgrass seed germination coincides with Forsythia blooms.

Crabgrass will not become highly visible in lawns and gardens until mid-summer. It is a coarse, unsightly, low growing and spreading plant. When young, it has light green foliage but takes on a purple appearance when it goes to seed. The leaf blades are approximately 1/4 inch wide and may be hairy or smooth. Seedheads appear as several finger-like projections on top of upright stems. Crabgrass plants die after the first frost in the fall.

In flower gardens, crabgrass will nestle in amongst the flowers and only the site of the seedheads will let you know you have a problem. By this time, the crabgrass has a firm hold on the soil and many of the seeds will have dispersed.

To prevent crabgrass invasion in flower gardens, the best method is to apply mulch around the plants in order to keep sunlight away from the soil. Several mulching materials are available including bark, cocoa hulls, compost or stone; the selection depending upon the appearance you are looking for. Mulching, along with thorough surveillance, should keep the beds crabgrass-free. Crabgrass is more of a problem in hot, dry conditions and will rarely threaten shade gardens.

The best way to prevent crabgrass infestations in lawns is to maintain a thick, healthy lawn through proper maintenance practices. A dense turf cover will not allow crabgrass or any other weeds to invade. If, however, the lawn has suffered some damage by winter injury, chinch bug or is thin in some locations, crabgrass can be a problem. The key to successful control of crabgrass in lawns is the correct timing of pre-emergent crabgrass controls.

Pre-emergent control means applying the chemical before the seeds have germinated. Most crabgrass control products are mixed with fertilizer so that you are able to apply the chemical safely through a broadcast spreader and fertilize at the same time. The chemical works by forming a protective blanket over the soil and preventing seedlings from forming. Many broadleaf weeds and most grasses will also be prevented from germinating with crabgrass control products. The chemical should not be used on newly seeded lawns or if you are seeding the area with wildflower seeds.

Timing is critical in crabgrass control. If controls are applied too early, crabgrass that germinates late in the season will not be controlled. If controls are applied too late, some crabgrass will already have germinated and will escape the treatment. A new product has recently been introduced, called Dimension, which will lengthen the time period for effective control since it also kills crabgrass in the early seedling stage.