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.
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.
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.
Using Weed and Feed
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.
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.
Sara DeBerry is a graduate of the University of Florida holding a masters degree in environmental horticulture and a minor in entomology and nematology. DeBerry has been writing for government agencies since 2004 and has published peer reviewed scientific articles during her studies at UF.
One common question I am asked every Spring is, “Should I seed my lawn in Spring or Fall?” Many homeowners are eager to start thickening up their lawn as soon as they get a glimpse of good weather in early Spring. We sometimes still have a late March snow on the ground when the calls start coming in. My answer to their question is the ever-popular “It depends.” After explaining the pros and cons to many homeowners over the years, I’ve put my recommendation in writing on this page.
Seeding in Spring or Fall? A common question from homeowners.
If you seed your lawn in early Fall, the seedlings will have 9 to 10 months to develop deeper root systems before they have to experience their first Summer of hot and dry weather. Compare this to 1 or 2 months for a Spring seeding, and the chances of an early Fall seeding surviving to maturity are significantly greater. On top of that, you can still apply your pre-emergent in Spring and keep out the crabgrass and other weeds throughout the season.
Grass plants depend on deep, healthy roots, and a tall, thick stand of grass blades to help it survive the stresses of Summer. Deep roots allow the grass to reach moisture that lies beyond the dried out top layer of soil. A tall and thick stand of grass blades help to shade the soil and prevent weeds from competing with the lawn. When you seed in the Spring, the new grass plants may come up very nicely after a few weeks, but under the soil, the roots will not yet be deep enough to survive Summer without a significant amount of irrigation from a sprinkler system. Unless you keep the seedlings watered all summer long and into early Fall, the chances of their survival is slim to none.