Keeping weeds out of your lawn

Weeds interfere visually with the uniform carpet effect that lawns provide. A few invaders do little harm, but large patches of weeds rob water and nutrients from the grass, weakening the lawn. These easy steps will tell you how to keep weeds from overtaking your lawn.

Healthy, vigorous lawns are naturally resistant to weeds. If you fertilize properly, water deeply and mow high, grass will grow so thick that weeds won't have a chance. However, stressed lawns are vulnerable to dozens of weed species.

Some, such as chickweed and crabgrass, are shallow-rooted annuals that die back after setting seed. Others, such as plantain and dandelion, are tenacious, deep-rooted perennials and will return year after year.

To halt the spread of annual weeds, you need to stop adult plants from dropping seeds and stop seeds from sprouting. Pull up annual weeds before they can set seed. If seedheads are already visible, use a bag attachment when mowing and compost the clippings, because compost piles often become hot enough during decomposition to destroy the seeds.

If seeds drop, you can spread a commercial pre-emergent herbicide, which is a substance that prevents seeds from developing. There are several broad-spectrum, granular pre-emergents available at garden centres that you can broadcast with a fertilizer spreader. An organic pre-emergent derived from corn is also now available from garden suppliers. Because crabgrass is so common, there is a pre-emergent designed just to control this weed.

1. Apply weed preventers according to package directions at the right time, which is shortly before weed seeds are germinating in your region. You will not be able to spread grass seed for the length of time designated on the package label after applying a pre-emergent weed preventer, because it will also keep grass seed from sprouting.
2. Perennial weeds must be dug out, roots and all. The easiest time to do this is when plants are young, when they have small roots, and after a rain, when the soil is soft.
3. Be sure you take out the entire root, especially of deep-rooted weeds, such as dandelion or those with spreading, fibrous roots, such as violets.
4. You can also apply an herbicide for perennial weed control, which is usually a liquid that you can either spray on individual weeds or spread on a large area with a hose-end sprayer.
5. No one product destroys all types of weeds or is safe for all grasses, so read the label carefully and use according to package directions.
6. To be most effective, these herbicides should be applied when the perennial weed is actively growing, usually just after the plant flowers.
7. Weeds should begin to shrivel and die in about 10 days. It is important to follow safety practices when spraying herbicides. Notify your neighbours that you will be spraying.

• Spray on a still day, so wind won't carry it onto desirable plants.
• Wear long-sleeved and long-legged clothing, socks and protective gear, including a respirator, goggles and gloves.
• Do not eat, drink or touch your hands to your face while spraying and bathe immediately after applying the product.