If you’re planning to plant new grass seed, it’s important to know how long you need to wait after applying weed killer. Most chemical weed control products require a waiting period before grass seed can be safely planted and grow properly. Here’s what you need to know about timing your weed killer applications and grass seeding.
Why Should You Wait ?
Not allowing enough time between spraying weed killer and planting grass carry risks, including:
Germination Issues – Weed killers are designed to disrupt plant growth. Residual chemicals in the soil can prevent proper grass seed germination.
Root Stunting – Even if new grass seeds germinate, the roots may struggle to establish and grow after exposure to weed controlling chemicals.
Plant Health Problems – Weakened grass plants are more prone to disease, nutrient deficiencies, and environmental stress.
Poor Growth – Grass may establishment but have stunted growth, irregular color, or be more sparse when planted too soon after weed control applications.
Following the recommended waiting periods helps avoid these problems and lets your new grass establish its best growth.
Waiting Periods by Weed Killer Type
The required waiting time between applying weed killer and seeding grass depends on the specific herbicide used:
Selective herbicides are formulated to target specific types of weeds while sparing grass and other desirable plants. These herbicides are commonly used for spot treatments or to control specific weed species. It is advisable to wait for at least 2-4 weeks after using a selective herbicide before planting grass seeds or laying sod.
Non-Selective Weed Killers
Non-selective herbicides like glyphosate (Roundup) kill all actively growing plants they come into contact with. Wait at least 2-3 weeks after applying before grass seeding. For best results, wait 6-8 weeks.
Pre-emergent weed killers disrupt root development and are designed to prevent seeds from germinating. These require longer waiting periods, typically 2-4 months before planting new grass.
Selective Post-Emergent Herbicides
Selective weed killers only kill specific weeds like dandelions or clover but won’t harm grass. You can often seed grass right after application as long as you follow label instructions.
It’s important to note that these waiting periods are general guidelines, and specific product instructions should always be followed. The waiting period may also be influenced by factors such as weather conditions, soil type, and the health of your existing grass.
Other Factors Affecting Timing
Besides the weed killer used, other factors influence how long to wait between application and grass planting:
Higher concentrations or heavier application rates mean it will take longer for the weed killer to break down in the soil. Wait longer with heavy doses.
Method of Application
Spray applications break down faster than concentrated granules. Adjust waiting times accordingly.
Weed killers break down slower in heavy clay soils than light sandy soils. Extend waiting periods if planting in heavy soils.
Hot, sunny weather speeds breakdown while cool and cloudy conditions slow it down. Account for recent weather patterns.
Some grass varieties are more sensitive than others. Wait longer if seeding with delicate, slower growing grass.
Following label guidelines provides a general timeframe but it’s important to account for these other factors when planning your weed control and grass seeding schedule.
Tips for Planting After Weed Killer Application
Here are some tips for getting the best results when planting grass after using weed killers:
- Always follow label instructions and wait the recommended time periods
- Conduct a small test seeding to check if grass can germinate properly
- Consider longer wait times if using high application rates or planting sensitive grass varieties
- Till or rake up treated soil and reseed into untreated soil below if planting sooner than advised
- Water newly planted grass frequently to dilute any remaining chemicals
- Repeat weed control applications if needed on any weeds that emerge after grass is growing
- Use weed control methods that are compatible with grass before initial seeding, this avoids the planting delays of pre-emergent weed killers
Careful timing when planting grass after weed killer use leads to lush, healthy turf. With a bit of patience and planning, you can time applications and seeding appropriately.
It’s always essential to check the label of any weed killer and follow the provided timing guidance based on product formulation and usage specifics. But these general rules can give you an initial estimate for planting grass safely after weed control.