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Each season of the year has its maintenance requirements, including dealing with weeds before and after they show up. Herbicides and fertilizers are formulated to be applied at a particular type in the growing stage of weeds and grasses, and some products are less interchangeable than others.
Pre emergent herbicides and weed and feed products aren’t substitutes for each other. Not only does herbicide not contain any fertilizer, weed and feed products more frequently contain post emergent weed killer rather than pre emergent. If you’re thinking about where these fit into your annual maintenance routine, knowing the differences will help you decide when, and if, to apply one or the other.
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Why Am I Getting Weeds?
Most weeds grow by seeds that are dispersed by wind or animals, and this is the case for both broadleaf and grassy weeds. They might grow the year they are dispersed, or they may stay mixed in the soil for several years before they germinate. When deciding whether to apply pre emergent herbicide or a weed and feed product, the condition of your lawn will help you figure out the best strategy to manage unwanted growth.
Thin coverage, bare spots, and over or under-fertilizing all encourage weed growth in a lawn. The first line of defense against weeds is a thick, healthy lawn. Dense turf coverage suppresses weed growth, blocking sunlight and not giving any space for other plants to pop up amongst the grass.
Pre Emergent Herbicides
Weed killer that suppresses germination is known as a pre emergent, acting before the plant emerges from the seed. Pre and post emergent herbicides alike are targeted at specific weeds and are made to be safe on specific types of grass.
The most common active ingredients in pre emergent formulas are prodiamine and dithiopyr. These are found in both isolated forms and in many weed and feed products.
Pre emergent herbicides can interfere with germination of desirable seeds as well and shouldn’t be applied in the same growing season as when you reseed. These are best applied to suppress unwanted growth to allow your lawn to revive from dormancy without competition.
A pre emergent is usually applied when temperatures are still below 55 degrees. This is so it lasts longer before the temperatures warm up enough to start weed and grass growth. Be sure that the soil temperatures aren’t too low; however, since to work best, pre emergent need to be watered in and worked into the soil.
Weed and Feed
Products that contain both herbicide and fertilizer can come in both pre and post emergent formulas, and each product will list specifically which kind it is and which weeds it targets. Crabgrass preventers, for example, frequently come as a fertilizer mix because grassy weeds are difficult to treat once they show up. By suppressing the grassy weed growth and feeding your lawn, these work together to prevent crabgrass before it can show up, while adding nutrients to the soil for when your lawn comes out of dormancy.
Other weed and feed products contain post emergent herbicides. They are usually targeted at broadleaf weeds like dandelions and clover, and these formulas support the grass as it grows while getting rid of weeds that grew in beside it.
Can You Put Down Pre-Emergent And Weed And Feed At The Same Time?
There isn’t any need to apply both a pre emergent herbicide and a weed and feed product at the same time. If you have a weed and feed formula made with a pre emergent, you would over-apply with a second dose of concentrated herbicide. Over-application can harm the lawn, especially the roots.
Similarly, since pre emergent weed killer should be applied in very early spring, any weed and feed product for post emergent weeds that you might use will be applied several weeks later in the growing season, after the pre emergent herbicide has done its job and has been rinsed away.
How To Apply Herbicides And Fertilizers
- Identify weeds for targeted herbicide – No single product targets all weeds (and if it does, it will harm your grass as well!), so always be sure to read the label to know what grasses the product is safe on, and which weeds it will get rid of.
- Soil temperature timing – The colder the weather, the slower weed killers work. For pre emergent, this helps it stay in the ground longer to suppress germination longer, and it should be applied when soil temperatures are still under 55 degrees.
- Follow directions for the application rate – The rate at which you apply pre emergent weed killer makes a difference: if you walk too fast or too slow, results can vary. Too little herbicide won’t have an effect, but too much can be hard on the grass as well. The rate should be listed, and it should be measured out in the amount prescribed for your lawn size.
Is Scotts Weed And Feed Pre Or Post Emergent?
Scotts Weed and Feed is a post emergent formula that targets dandelions and clover, among other post-emergent weeds. For a crabgrass preventing pre emergent herbicide, Scotts Halts Crabgrass Grassy Weed Preventer targets weeds without giving the yard fertilizer too early.