NEWLY SEEDED LAWNS: The best way to keep weeds out of the lawn is by following the proper steps in planting: First, use a high quality grass seed. Other important aspects in keeping weeds out of new lawn include using good topsoil and weed-free organic matter as well as seeding at the proper rate and watering on a correct schedule. It is important to note that when a lawn is first planted from seed it will always have weeds in it. It is vital not to spray lawn weed killer or use a weed and feed on the lawn until it has been mowed at least three to four times and is well established. Also, lawn weed killers should not be used in the middle of the summer due to the excessive heat. They are best used in the spring and fall.

ESTABLISHED LAWN: The best way to keep most of the weeds out of an established lawn is by keeping it healthy so that the strong grass can choke out the weeds that would infest it. Some ways to keep the lawn healthy are mowing at a height of 2 ½ to 3 inches every four to five days, watering less often with greater amounts of water, fertilizing about every six weeks and aerating once a year. Because it is almost impossible to keep all weeds out, having a few will not harm your existing lawn.

If a lawn's health is being maintained, but weeds are still present, it is important to identify what kind of weeds are in the lawn before trying to control them. Weeds come in two forms, broadleaf weeds (dandelions and clover are two examples), and weedy grasses (Crabgrass and Bermuda grass, etc.).

Controlling broadleaf weeds in the lawn is often easier than getting rid of grasses. Many broadleaf weeds, which germinate in the spring, can be controlled by applying a pre- emergent weed killer. Pre-emergent weed killers are usually combined with a fertilizer and work by killing the weeds as they are attempting to germinate. In Northern Utah, pre-emergents, need to be applied by mid-March or early April to be most effective.

In the spring or fall, liquid weed killers such as Trimec® and Speedzone® or granular weed-and-feed can be applied to kill broad leaf weeds. Trimec often takes up to two weeks to kill out problem plants but still kills very effectively. Speedzone is a little more expensive than Trimec but kills much more quickly and works better on harder-to-kill weeds such as bindweed (morning glory). If there are not many weeds present in the lawn, granular weed-and-feed fertilizers can also be used in the spring, but they are not quite as effective as the liquid herbicides.

To control weedy grasses in the lawn, it is important to maintain its health. Once the weed grasses are growing, all that can be done is spraying them out with Round-Up® or other broad spectrum weed killers containing glyphosate. After spraying with these chemicals, reseeding or re-sodding will be necessary in the area. There are no weed-killers specific enough to kill weed grasses growing in the lawn without killing the lawn itself. Because left over roots can spread in the soil, do not dig out the weed grasses until they are dead.