Even if you time your weed preventer and seeding periods correctly, you need to do the job right to get an even lawn with no bare patches. Apply seeds uniformly across your yard using a drop spreader on a mild fall day. Spread up to 1-inch of organic mulch over the seeds to conserve moisture and encourage germination. Water the seeds at least twice a day for short, 10-minute sessions. You do not want to wash away the seeds, but they need consistent moisture to grow. Hand pull any weeds that appear while the grass seedlings develop. Do not apply any chemicals for weed control.
Avoid the need for weed preventers by keeping your lawn healthy. Once established, only water your turf once a week during the growing season. Up to 1 inch of water during this watering session allows roots to search deeply for moisture to create strong grass. Shallow grass roots die in stressful conditions, like drought, and allow weeds to grow in thinned spots. Allow your turf to grow to a healthy height as well, typically between 1 and 3 inches, depending on the species. Long grass blades mean the grass can produce enough energy to stay healthy and compete with weeds. In short, healthy and well-maintained grass has less problems with weed growth.
Spreading seed is an inexpensive way to grow a lush lawn, but exposed soil between germination and establishment makes it vulnerable to weeds. Although chemical weed preventers have different mixtures and instructions, you should not apply them while seeding or immediately afterward. You must allow one to four months between applying this type of chemical and spreading seed.
Chemical weed preventers, also called preemergent herbicides, are usually granules or liquids, but both require water to work. As the preventer soaks into the ground, it leaves a residual film in the top 1-inch of soil. Because most seeds germinate at or just below the soil’s surface, these preemergent herbicides remain active against any germination processes for up to four months, depending on the chemicals involved. Organic weed preventers work in a similar way. With many weeds being members of the grass family, all seeds, including desired lawn species, fail to germinate and sprout after you’ve used a weed preventer.
Cool-season grasses are usually seeded, as opposed to warm-season grasses that usually need to be grown from sod or plugs. Because cool-season grass seeds germinate best in fall, apply your chemical preventer in spring to actively kill off weeds in spring and summer. In general, temperatures between 65 and 70 degrees Fahrenheit are good for weed preventer application. Hot days often cause the chemicals to vaporize into the atmosphere, reducing their effectiveness. By the time fall seeding weather arrives, the chemicals are no longer active and the grass seeds will be able to sprout.
Writing professionally since 2010, Amy Rodriguez cultivates successful cacti, succulents, bulbs, carnivorous plants and orchids at home. With an electronics degree and more than 10 years of experience, she applies her love of gadgets to the gardening world as she continues her education through college classes and gardening activities.
Chickweed (stellaria media): This is a very pesky annual plant that appears all across the U.S. as low-growing vine-like stems with small egg-shaped leaves and tiny white flowers. While major infestations are best treated with a pre-emergent herbicide applied in fall, plants that appear in spring can be spot-treated with a post-emergent broadleaf herbicide. Chickweed is also fairly readily killed by spraying with ordinary household white vinegar. Keep your lawn mowed short to prevent the plant from flowering and setting seeds.
Purslane (Portulaca oleracea): This annual weed grows in low mats with reddish stems and oval-shaped succulent leaves. It becomes a more severe problem in the humid, hot days of later summer, but you may see early plants appear in spring. It is a fairly easy plant to prevent by application of a granular pre-emergent herbicide, and it is readily killed by spot treating with a post-emergent broadleaf herbicide. And it is quite easy to break off the plant at ground level, which will prevent it from flowering and setting seeds. This may be the best choice of all, as purslane is an exceedingly healthful plant that rivals spinach for sheer nutritional value. It can be eaten raw in salads or sauteed as a side dish. Naturally, it should not be harvested for eating if you have applied any herbicide in the area.
Spending an hour or so once a week pulling weeds by hand after mowing is completed can keep a lawn largely free of most weeds.
Don’t give up, however. While achieving and keeping that dream lawn does require some year-round attention, a diligent approach in spring means you’ll spend more time enjoying your lawn and less time maintaining it through the summer and into fall.
The chemical weedkillers (herbicides) most commonly used on lawns can be formulated to kill broadleaf weeds like dandelions and chickweed, or they can be designed to kill other competing grass-like weeds, such as crabgrass, quackgrass, and nutgrass. There are also combination products, containing the chemicals to kill both broadleaf weeds as well as grassy weeds.
Beyond this, chemical herbicides come in two general categories: pre-emergent and post-emergent. A pre-emergent herbicide is a weed killer applied prior to the germination of the weed seed and the subsequent emergence of the weed seedling from the soil. Pre-emergent herbicides are sometimes applied in the late fall in warm-weather regions, but in cold-weather regions, they are usually applied in the early spring before the turf grasses have begun to actively grow. One advantage of pre-emergent weed killers is that they can prevent mid and late-summer weeds, such as plantains, before they even appear.
Crabgrass (Digitaria spp): Crabgrass gets its name from the leaves, which form a tight, crab-like circle. This annual weed tends to appear in weak or bare areas of a lawn. Both over- and under-watering favor its growth, as does consistently mowing the lawn too short. Crabgrass can be treated with pre-emergence herbicides in the spring, which will keep the seeds from sprouting, or they can be treated with post-emergent herbicides as the weeds are noticed, beginning in spring. Check with your local extension office or a reputable garden center to fine-tune timing in your region. Crabgrass clumps can also be removed by hand, which is best done when the lawn is quite moist.
While it is best to over seed in fall, after applying your preemergent, it’s important to give your lawn some time to for the product to lose its effectiveness before moving on to the next step. Therefore you shouldn’t be overseeding immediately after applying this herbicide – it’s best to wait at least 4 months between. If you must seed sooner some detailed prep work must be completed to assure you have a quality seed bed that won’t be harmed by the pre-emergent herbicide.
Can I overseed after applying pre-emergent?
When should I apply pre-emergent?
Whether your lawn is a small patch of grass or several acres, it’s important to take care of it properly to keep it healthy all year long. The pros at Loyalty Lawn Care know the tips and tricks to keep your lawn green. But what about grassy weeds like crabgrass and foxtail? These pesky plant pests can overtake an otherwise healthy lawn and cause problems aside from the obvious visual concerns. The best way to ensure that these grassy weeds don’t ruin the look or health of your lawn is to use pre-emergent.
What is pre-emergent?
Often used alongside fertilizer, pre-emergent is not fertilizer itself. Instead, it is an herbicide that works to prevent grassy weed seeds from germinating. The reason that it is used in conjunction with fertilizer is because the latter is an effective carrier agent for the pre-emergent to bind to. This product is often referred to as weed and feed.
Every pre-emergent product is a bit different, but you can expect a single treatment to last approximately 3-5 months.