Have questions about when and how to seed your lawn this spring? Consult Spring Green's Lawn Care Guide for all the answers! Learn how to kill weed seeds in soil to prevent weeds and other invasive grasses from continuing to sprout every year. Weed control is the biggest problem facing wildflower establishment for direct-seeded projects. Learn more about weed control methods in wildflower gardens.
6 Things to Consider Before Seeding In The Spring!
It’s spring! The weather is becoming warmer, and you’re ready to get outside and turn your attention to lawn and landscape projects. While spring may seem like a great time to seed some of those thin or brown patches in your lawn, it may be better to wait. Here’s why. Spring seeding makes it difficult to effectively control annual weeds, such as crabgrass, with pre-emergents. Pre-emergents stop weeds by creating a barrier below the soil surface to keep the weeds from ever sprouting. However, the same pre-emergent that kills crabgrass seedlings will keep your new grass from sprouting, too.
Putting off your early spring application of pre-emergent weed control can give crabgrass, and their weeds, a strong foothold. Once established, crabgrass spreads very quickly and can crowd out your new grass. Choosing to seed after pre-emergents have been applied also presents problems. Raking, or cultivating, the soil for planting will break the pre-emergent barrier under the soil and decrease its effectiveness. Conditions are best for planting lawn seed in the fall. Soil temperatures are ideal in late summer and early fall for quick germination of your lawn seed. Seeding in the fall allows your new turf to develop a strong root system before heading into the next season’s hot, dry summer months.
If Spring Seeding Can’t Wait, Consider These 6 Things!
- Wait to sow your seeds until soil temperatures reach 55 degrees (use a meat thermometer to check soil temperatures at a 1” depth).
- If you have bare spots that you must seed in the spring, mark the seeded areas with straw or light mulch so pre-emergents can be avoided in those areas.
- Keep the seeded area well watered, as crabgrass thrives in dry soil.
- Mow the area normally once the new grass is as tall as the rest of the lawn, to avoid the new turf growing too tall and lanky.
- Weed control applications should be avoided on the young grass until it has been mowed 3 to 5 times.
- If you plan a general, or large area seeding, a special program of crabgrass control should be worked out to prevent problems in the summer.
For further information, visit our core aeration and overseeding page or contact your local Spring Green professional
How to Kill Weed Seeds in Soil [5 Easy Methods]
To kill weed seeds in soil you will have to apply one or more of the following methods:
- Heat soil to temperatures high enough to kill weeds seeds
- Force seeds to sprout and destroy growing weeds
- Apply chemical or natural weed killers that prevent weeds from sprouting
- Use flame weeding to destroy weeds and seeds at once
- Layer mulch in garden areas to suppress weed sprouting and attract insects that eat seeds
With this arsenal of tricks for killing weed seeds before they sprout, you can stop the spread of weeds in both your lawn and garden.
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5 Tips for Killing Weed Seeds
Rather than spending time and effort battling weeds as they sprout, attack weeds at the source by killing weed seeds. Each of these methods destroys weed seeds, which ensures you won’t have to battle recurring weed invasions. Try these ways to get rid of weed seeds yourself.
Soil solarization is a very powerful method for killing weed seeds. Weed seeds begin to die if soil temperatures surpass 108 degrees, with full seed death ensured by soil surface temperatures of 140 degrees or more. Solarization uses clear plastic tarps to trap heat at the soil surface, killing weed seeds within the tarped area. To solarize an area, follow these steps:
- Clear the area of all vegetation through use of a hoe or other garden implement. Remove any woody stumps
- Till the soil to further break up any weed root systems left behind.
- Rake away all vegetation residue
- Water the tilled and cleared soil with a garden hose until it is damp.
- Lay a sheet of clear plastic over the area. Weigh it down tightly at the edges
- Leave the plastic in place for at least two months.
Solarization is the best method to reclaim a weedy garden or other area. It is a “clean slate” for your soil, because seeds will be destroyed by the solar heat trapped beneath the plastic.
It is typically tough to implement solarization in large areas and is not usually suitable for use in lawns, where you may want to preserve grass or other plants. Pre-emergent weed killers and flame weeding are much better for use in lawns.
Till and Kill
Weed seeds can lie dormant in soil for decades and are only “activated” when brought to within an inch of the surface. One method to rid soil of dormant weed seeds is to force these dormant seeds to sprout, then attack them with a powerful natural or chemical weed killer. To do this:
- In spring, till the affected area. Tilling brings dormant seeds to the surface
- Water the area for 1–2 weeks with a sprinkler or soaker hose
- When weeds begin to sprout, apply the weed killer of your choice
This is another “clean slate” method, where you force weed seeds to show themselves and then kill young weeds before they mature and cast seeds. Because of the invasive tilling step, it is not best used in areas with desirable grasses and plants.
Use Pre-Emergent Weed Killer
Pre-emergent weed killer stops weeds in their tracks. It works by attacking weed seeds just as they begin to germinate, killing them before they even poke above the surface. It’s a weed killer so good, the only sign it’s working is that there will be no new weeds at all.
The Importance of Removing Weeds and Weed Seeds in Your Planting Site
Weed control is the biggest problem facing wildflower establishment for direct-seeded projects and one which has no easy solution. Weed seeds are present in many situations and lie dormant, but viable, for long periods. A weedy area converted to wildflowers will have a large reservoir of weed seeds in the soil, ready to germinate when conditions are favorable. In most cases, it is advisable to consider weed control in two phases – as part of site preparation prior to planting, and as an important component of a post-germination maintenance program.
Weed Control Methods
Before planting, existing weeds and unwanted vegetation can be removed in a number of different ways.
- Using the no-till method
- Applying a non-selective, non-residual herbicide such as a glyphosate product
- A combination of tilling and an herbicide.
- For additional weed control after site preparation, a soil fumigant that kills weed seeds may be used
Smothering of existing weeds and vegetation is an option for small-scale planting projects and can be done with black plastic that is UV stabilized. This method “cooks” the vegetation and weed seeds in the topsoil. The edges of the plastic should be covered with dirt to prevent airflow underneath the plastic. This is a good option if you wish to avoid the use of herbicides. However, smothering usually takes a full growing season to successfully kill perennials that can regrow from the roots.
Repeated tilling is another good option if you wish to avoid the use of herbicides. The initial tilling removes the existing vegetation, and then repeated tilling every three weeks for a full growing season will help to deplete the weed seeds in the soil by killing newly sprouting weeds. In dry areas, providing supplemental water will encourage weed germination and regrowth so that repeated tilling can be effective.
An effective, no-till method to prepare a seed bed is to apply a glyphosate herbicide and allow the vegetation to die back (usually about 10-14 days). Use a scalper to remove the dead thatch and scratch up the soil surface. The top surface of the soil is lightly roughened by the scalper and makes a good seed bed. Once seeds are sown, go over the area with a roller or cultipacker to cover the seeds.
Methods for Extremely Weedy Areas
- Till soil or spray vegetation with glyphosate herbicide. When using an herbicide, allow vegetation to die, then rake out the dead debris. If aggressive, perennial weeds such as bindweed are present, using an herbicide is more effective than tilling.
- Irrigate to encourage germination of weed seeds near the surface; most seeds will germinate within two weeks if consistent moisture is available. Do not till the soil again because this will bring even more weed seeds up to the surface.
- Spray any new growth with glyphosate herbicide.
- After raking out dead vegetation, allow soil to recover for 3-4 weeks before planting seed.
Once the seeds have germinated, further weed control is usually necessary. If practical, pull all weeds as soon as they can be identified. Other successful techniques are spot-spraying with a general herbicide or selectively cutting weeds with a string trimmer. Be sure to remove weeds before they reseed.
Many unwanted annual and some perennial grasses can be controlled with the herbicides Grass-B-Gon®*, Ornamec®* and Fusilade®*. These post-emergents do not affect broad-leaved plants so they can be applied over existing flowers; they are most effective when sprayed on new growth and young plants. Take care to avoid treating areas with desirable native grasses or fescues.
*Observe all precautions and follow manufacturer’s recommendations for application.