It’s important to know a little about herbicides so you can make the best choice for when to apply seed in an area that has been treated for weeds. The most common types of herbicide in weed and feed products are selective and systemic. Selective herbicides target a species of plant to kill while systemic herbicides work by being absorbed though the roots and then transported throughout the plant, killing it from within. Read the bag label to see what kind of herbicide is used in the weed and feed you are considering using or have used. The bag label will tell you how many days you must wait before applying seed to a lawn that has been treated with that product.
Weed and feed fertilizers are often used in combination with seeding. Weed and feed formulations consist of two components: a herbicide to kill weeds and a fertilizer to strengthen the turf. The herbicide will weaken the grass as well as the weeds and the fertilizer will strengthen the weeds as well as the grass. When applying seed over a weed and feed application, remember that some weed and feeds can prevent grass seeds from growing.
It is important to know what kind of grass you have growing or want to have growing. Certain chemicals act differently on different species of grass and weeds. For example, the common herbicide 2,4-D is toxic to some cultivars of St. Augustine grass (Stenotaphrum secundatum), which grows in the area roughly covered by U.S. Department of Agriculture plant hardiness zones 8 through 10. Another common herbicide, atrazine, is potentially lethal to grass when applied in temperatures above 85 degrees Fahrenheit. Use the instructions on the bag of each weed and feed product to determine how it will affect seeding.
Only use a weed and feed if the weed infestation is completely uniform over the entire lawn and all species of weeds targeted will be affected by the herbicide in the weed and feed. This scenario doesn’t occur often, so it is more likely the use of an herbicide and a fertilizer separately will be needed. If the weeds are uniformly spread over the area to be treated, match the appropriate weed and feed product to your grass, the seed you have recently applied or want to apply, and the time of year.
Herbicides can target weeds before they germinate from seed – pre-emergent – or as developed plants – post-emergent. Before you seed, you can use a non-selective, post-emergent herbicide to control any weeds in the area to be seeded. Most of these can be applied up to two weeks before seeding to control any existing weeds. Herbicides should not be used after seeding until the new seedlings are established. Mowing and spot treatments can be used to control weeds until the seeded area is actively growing and requires only maintenance watering. Establishment times vary depending on the type of seed you use and your weather conditions.
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.
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.
Time It Right
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.
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.
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.
Don’t overdo or cut corners. Too much grass seed causes undue competition for resources such as light, water and nutrients, and grass seedlings struggle as a result. Too little seed leaves lawns thin or bare. Always follow “best practice” guidelines for planting grass seed, including site preparation and good seed-to-soil contact, and stick with recommended seeding rates for lush results.
For most of the country, fall is the best time to plant grass seed. This is when cool-season grasses such as Kentucky bluegrass and tall fescues peak in growth, and conditions enhance fast germination and establishment. When paired with innovations such as water-conserving Pennington Smart Seed, proper timing leads to other advantages, including less input of resources, less maintenance and better results.
Seeding success depends on an environment conducive to good grass growth. Knowing how your soil measures up on certain essentials, such as soil pH and plant nutrients, allows you to provide the foundation an outstanding lawn needs. Soil testing processed through a reputable soil laboratory eliminates guesswork and reveals changes you need to make.
4. Ignoring recommended seeding rates
One of the ways weed treatments work is by preventing germinating seeds from establishing roots. But these products, known as pre-emergents, can’t distinguish between harmful weed seeds and desirable grass seed you put down. Using these products too close to newly planted seed — in timing or proximity — stops grass seed in its tracks, along with the weeds. Post-emergent weed treatments aimed at existing broadleaf weeds can also injure immature grass seedlings.
Knowing your total property size is just the start. All non-lawn areas must then be deducted. This includes the footprints of your house, garage and outbuildings, as well as walkways and the driveway. Only then can you calculate your actual lawn area and the amount of seed you need. Time spent on proper measurements prevents wasted product, wasted money and poor results. Get it right and every bit of seed and labor work in your favor.
Without knowing where your soil stands, well-intended soil amendments and fertilizers can harm grass instead of help — or simply go to waste. Incorporating your specific soil lab recommendations helps circumvent potential problems and unnecessary setbacks. That’s one reason turf professionals emphasize regular soil testing to start seed right and keep lawns healthy and vibrant. Your local county extension office can help with testing kits and lab referrals.
Even with similar seed types, all grass seed isn’t equal. Learn what’s actually inside the seed bags you or your lawn professional buy. By understanding the seed tags on grass seed products, you can be sure you invest in quality seed. Cheaper price tags can mean less seed versus fillers, old seeds past their prime, more weed seeds and lower germination rates. Getting seed right from the start benefits your lawn and budget.