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.
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.
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 By the time fall seeding weather arrives, the chemicals are no longer active and the grass seeds will be able to sprout.
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.
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.
Before you plant grass seed, you should always prepare the area by removing any weeds that may be growing in the location. Even with careful preparation of the planting site, weeds can still develop among the newly planted grass seed. Weed killers, however, can harm grass seeds and seedlings if applied too early or improperly.
Remember that all herbicides are different and the exact time you must wait to apply weed killers to newly planted grass will vary from one product to another. Also, some herbicides cannot be applied to certain species of turfgrass. For best results, always refer to the herbicide bottle’s label.
You can control weeds in newly planted grass seed and seedlings without the use of herbicides. Manually pulling the weeds by hand when they first appear keeps them from producing seeds and prevents the problematic plants from spreading, according to the University of California Statewide Integrated Pest Management Program website. They suggest keeping the newly planted grass weed free with proper mowing, irrigation and fertilization. Since newly planted turfgrass has short roots, keep the root zone moist by watering the soil lightly. However, avoid over saturating the soil. After the turfgrass has become established, promote deep and healthy root growth by watering infrequently but deeply.
A general rule of thumb is to wait at least until you have mowed the new grass four times before using any standard postemergent broadleaf herbicide. A standard pre-emergent herbicide should not be applied until at least three to four months after seeding the area.
Weed management should be completed before seeding the lawn with a non-selective herbicide seven to 14 days before you till the soil. A second application of the herbicide may be required to kill any weeds you missed during the first treatment. Wait another seven days until tilling the soil if a second application is used.
Every pre-emergent product is a bit different, but you can expect a single treatment to last approximately 3-5 months.
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.
In a word, no. Because newly seeded lawns are still germinating, the pre-emergent can affect germination in the process. More mature lawns are sturdier against the herbicide, so it’s best to wait at least 4 months after planting the lawn to apply the pre-emergent. If you are unsure about the best timeline to follow for your lawn, don’t hesitate to reach out to Loyalty Lawn Care with your questions.
Like many things when it comes to your yard, pre-emergent has seasonality to it. It’s most ideal to apply a pre-emergent herbicide before the temperature of the top 4 inches of soil reaches 55 degrees Fahrenheit for at least 5 days in a row. This translates to daytime highs of the upper 60’s to mid-70s for the same amount of time. We recommend considering a pre-emergent application in the late winter to early spring to maximize its effectiveness.
What is 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.
Can I overseed after applying pre-emergent?