Get Those Weeds Under Control!

Weeds are, by simplest definition, plants out of place. They're growing where we want other things - like a nice lawn - to grow.

While there are hundreds of different types of weeds that can turn up in a lawn, they are classified into three rather broad categories: grassy, broadleaf and sedge. Weed life cycles are either annual (they emerge from seed each year) or perennial (they live more than one year). Once you get a handle on the types of weeds in your lawn, you will be able to take the appropriate steps to defend against them

Remembering the Basics

Remember this about weed control — weeds are opportunists. They only grow where they are allowed to grow. That's why the best way to keep weeds out of a lawn is to do everything you can to promote a dense, healthy turf. This means following proper mowing, watering and fertilizing techniques. If you neglect these basics, weeds can take hold more easily.

Mowing your grass too short can promote weed growth by opening the turf canopy to extra sunlight. Here's a mowing basic: follow the one-third rule. In other words, never cut more than a third of the grass leaf blade with any single mowing. Mowing too closely, or scalping the turf, opens the turf canopy and makes it harder for the grass to compete with weeds. Even if your grass has grown too long due to weather conditions or your inability to get the mower out at the appropriate time, never take off more than one-third of the leaf blade. This means you may have to mow twice that week, but it is better for your lawn.

Improper watering and fertilization also invite weeds. Too much or too little of these essentials can stress the turf, resulting in open areas for weeds to take hold. A combination of poor practices, like too much fertilizer coupled with scalping the grass, invites opportunistic weeds to move in.

Pre-emergent for Crabgrass

It's best to control weeds when they are young. That's because older, tougher weeds are often immune to any chemical control. Stopping weeds early in their life cycle means controlling grassy weeds (crabgrass, foxtail, goosegrass) with a type of herbicide called "pre-emergent", which blankets the soil to prevent young weeds from breaking through the surface. Meanwhile, the treatment for broadleaf weeds like those pesky dandelions and sedges is a post-emergent type herbicide that kills these plants after they appear.

The most prevalent summer weed in lawns is crabgrass. Crabgrass is an annual that germinates when soil temperatures warm up to 60 degrees. Pre-emergent herbicides are only effective if applied before the conditions for crabgrass germination are present.

Because spring weather conditions can be unpredictable, it's best to rely on biological signs rather than the calendar to determine when to apply herbicides. One very good indicator is the forsythia bush. This small, bright yellow flowering shrub is one of the first to bloom in the spring. Apply a pre-emergent herbicide before the blooms fall off and you will normally make the window. To control goosegrass, apply herbicide when lilacs are in bloom.

Pre-emergent herbicides work best when they completely cover the lawn or the affected area ("hot spot"). These products are designed to remain in the soil to prevent weeds from germinating throughout the summer. These products are nonselective in preventing seeds from germinating, so be sure to avoid newly seeded areas unless you are using a selective product like siduron.

Post-emergent for Broadleaf Weeds

Broadleaf weeds are best prevented in the fall (October and November) when they are just germinating. You'll need to apply a post-emergent herbicide and make sure the product sticks to the leaf surface.

To control dandelions in the spring, watch for the plants to produce a yellow flower; this is a good sign that the soil temperature is warm enough for several weeds to start growing. Take care to avoid applying the product just prior to rainfall because anything that washes the product off the surface will decrease its effectiveness.

Summer is the worst time to control broadleaf weeds. The waxy coating on many weeds during this time of drought or heat makes it difficult for the products to stay on the leaf surface or penetrate into the leaf. Your best bet is spot spraying with product formulations known as esters to successfully penetrate the waxy leaf surfaces.

Sedges can be a problem in some areas and are usually an indicator of over-watering the lawn. They can be controlled with post-emergent products, but the control must be backed up with good water management.

Weed-Free, Chemical-Free?

Is it possible to have a weed-free lawn without herbicides? Yes, but not without some work. You'll need to do some thorough hand pulling to get rid of existing weeds. Then, you'll have to stay on top of weed growth with good lawn care practices (one-third mowing rule, regular watering, etc.) to keep them out. Corn gluten meal is the most effective biological product for annual grass control. But this product has limitations and works best when the yard has at least 30 - 50 percent healthy turfgrass.