Long, narrow leaves with silver-green stripes running parallel to the veins make this philodendron easy to distinguish from similar varieties. But if you are staring at a lawn full of weeds, you are probably wondering does preen kill grass. The short answer is no, but there are some important details you need to know before you spread it everywhere.
Preen is a pre-emergent herbicide. It stops weed seeds from sprouting. It does not harm existing grass plants, which is why it is so popular for lawn care.
Does Preen Kill Grass
No, Preen will not kill established grass. The active ingredient, trifluralin, works by interfering with cell division in germinating seeds. Since grass roots are already established, they simply do not absorb the chemical in a harmful way.
However, you need to be careful. Preen will stop grass seeds from growing too. If you are overseeding your lawn, do not use Preen at the same time. You will waste your money and your seed.
How Preen Works In The Soil
Preen forms a chemical barrier on the top layer of soil. When a weed seed tries to germinate, it comes into contact with this barrier. The seed cannot develop a proper root system, so it dies.
This barrier does not discriminate between weed seeds and grass seeds. It stops all seeds. That is why timing matters so much.
- Preen stops seeds from rooting
- Preen does not affect mature grass roots
- Preen breaks down over time (usually 8-12 weeks)
- Preen needs water to activate
Which Preen Product Should You Use
There are several types of Preen. The most common one is Preen Garden Weed Preventer. This one is for flower beds and gardens. It is safe around ornamental plants but not around vegetable seeds.
Preen Lawn Weed Control is a different product. This one is a post-emergent herbicide. It kills existing broadleaf weeds like dandelions and clover. This product can be used on lawns without harming the grass.
Make sure you read the label. Using the wrong product in the wrong place can cause problems. The garden variety will not kill grass, but it will prevent grass seeds from growing if you scatter it on a bare patch.
When To Apply Preen For Best Results
Timing is everything with pre-emergents. If you apply Preen too late, the weeds have already sprouted. If you apply it too early, the barrier may break down before the weed seeds arrive.
For crabgrass, apply Preen in early spring. The soil temperature should be around 55 degrees Fahrenheit for several days. This is usually when forsythia bushes are blooming.
- Wait for soil temperatures to reach 55°F
- Apply Preen evenly across the lawn
- Water the lawn lightly to activate the barrier
- Do not rake or disturb the soil after application
- Reapply after 8-12 weeks if needed
Can You Apply Preen To A New Lawn
No. You should never apply Preen to a newly seeded lawn. The grass seeds will not germinate. You need to wait until the new grass is well established. This usually takes about four months after seeding.
If you are planting sod, you can apply Preen after the sod has rooted. This takes about two to three weeks. The sod roots are already established, so the Preen will not harm them.
What About Existing Weeds
Preen does not kill existing weeds. If you have dandelions or crabgrass already growing, you need to pull them out first. Or you can use a post-emergent herbicide like Preen Lawn Weed Control.
Once you remove the existing weeds, you can apply Preen to prevent new ones from sprouting. This is a two-step process. Remove the current problem, then prevent the future problem.
How Preen Affects Different Grass Types
Preen is safe for all common lawn grasses. This includes fescue, ryegrass, bluegrass, and Bermuda grass. The chemical does not differentiate between grass species. It only cares about seed germination.
If you have a mixed lawn, you are still fine. Preen will not cause discoloration or thinning. It simply sits in the soil and waits for seeds to try to sprout.
Potential Risks And Side Effects
While Preen is safe for grass, there are some risks. If you apply too much, the chemical can build up in the soil. This can make it hard for any plants to grow in that area.
Preen can also drift in the wind. If you apply it on a windy day, it may land in your flower beds or vegetable garden. This can prevent your vegetables from germinating.
- Always apply on a calm day
- Use a spreader for even coverage
- Sweep up any Preen that lands on driveways or sidewalks
- Keep pets and children off the lawn until the product is watered in
How Long Does Preen Last
Preen typically lasts for 8 to 12 weeks. This depends on the amount of rain and the soil temperature. Warmer soil breaks down the chemical faster.
If you live in a warm climate, you may need to reapply every 8 weeks. In cooler climates, you can stretch it to 12 weeks. Always check the label for specific instructions.
You can also use Preen in the fall to prevent winter weeds. Apply it in late summer or early fall. This will stop weeds like chickweed and henbit from germinating in the winter.
Alternatives To Preen For Lawn Care
If you are worried about using chemicals, there are alternatives. Corn gluten meal is a natural pre-emergent. It works the same way as Preen but is less potent. You need to apply more of it and reapply more often.
Mulching is another option. A thick layer of mulch can block weed seeds from reaching the soil. This is not practical for a full lawn, but it works well in garden beds.
Regular mowing and proper fertilization can also reduce weeds. A thick, healthy lawn leaves no room for weeds to grow. This is the best long-term strategy.
How To Apply Preen Correctly
Applying Preen is simple, but you need to be accurate. Use a broadcast spreader for large areas. For small areas, you can use a hand-held spreader.
- Calculate the square footage of your lawn
- Set your spreader to the correct setting (check the label)
- Walk in straight lines, overlapping slightly
- Water the lawn immediately after application
- Wait 24 hours before allowing pets on the lawn
Do not apply Preen before heavy rain. The rain can wash the chemical away before it binds to the soil. Light rain is fine, but heavy downpours are not.
Common Mistakes With Preen
One common mistake is applying Preen after the weeds have already sprouted. This wastes your time and money. Preen only works on seeds, not on growing plants.
Another mistake is not watering the Preen in. The chemical needs moisture to activate. If you leave it dry on the surface, it will not work. The wind will blow it away.
Some people also apply Preen too thick. This creates a heavy chemical layer that can harm beneficial soil organisms. Always follow the recommended application rate.
Does Preen Kill Grass In Flower Beds
Preen will not kill grass in flower beds either. But it will prevent grass seeds from germinating. If you have creeping grass like Bermuda grass, Preen will not stop it. This type of grass spreads through runners, not seeds.
For creeping grass, you need a different approach. You may need to use a non-selective herbicide like glyphosate. Or you can physically dig out the grass roots.
Preen is best for preventing annual weeds like crabgrass and foxtail. It is not effective against perennial weeds that spread through roots or runners.
Can You Use Preen Around Trees And Shrubs
Yes, Preen is safe to use around trees and shrubs. The chemical does not harm woody plants. You can spread it around the base of trees to prevent weeds from growing.
However, you should not use Preen around newly planted trees. The tree roots are still establishing. The chemical barrier may interfere with root development in young plants.
Wait until the tree has been in the ground for at least one full growing season. This gives the roots time to establish before you add any chemicals.
Environmental Impact Of Preen
Trifluralin is moderately toxic to fish and aquatic organisms. You should avoid using Preen near ponds, streams, or drainage ditches. The chemical can run off into water sources during heavy rain.
Preen is also persistent in the soil. It can stay active for months. This is good for weed prevention but bad if you want to plant new seeds later.
If you are an organic gardener, you should avoid Preen. It is a synthetic chemical. Corn gluten meal is a better choice for organic gardening.
How To Test If Preen Is Still Active
You can test if Preen is still active by planting a few fast-growing seeds in the treated soil. If the seeds do not germinate, the Preen is still working. If they sprout, it is time to reapply.
This is a simple test that takes about a week. Use radish seeds or lettuce seeds. They germinate quickly and are sensitive to trifluralin.
Alternatively, you can just follow the recommended reapplication schedule. This is easier and does not require any testing.
Frequently Asked Questions
Will Preen kill my existing lawn?
No, Preen will not kill existing grass. It only prevents seeds from germinating. Your established lawn is safe.
Can I overseed after using Preen?
You should wait at least 8-12 weeks after applying Preen before overseeding. The chemical needs to break down first. Otherwise, your grass seeds will not grow.
Does Preen work on all types of weeds?
Preen works on most annual weeds that grow from seeds. It does not work on perennial weeds or weeds that spread through roots or runners.
How long after applying Preen can I plant grass seed?
Wait at least 12 weeks after applying Preen before planting grass seed. The chemical barrier needs to break down completely. Check the label for specific timing.
Is Preen safe for pets?
Preen is generally safe for pets once it is watered in and dry. Keep pets off the lawn for 24 hours after application. The dry powder can be irritating if inhaled.
Final Thoughts On Preen And Grass
Preen is a safe and effective tool for preventing weeds in your lawn. It will not kill your grass. It only stops seeds from germinating. This makes it perfect for maintaining a weed-free lawn.
Just remember to time your application correctly. Apply it in early spring before weeds sprout. Water it in well. And do not overseed for at least 12 weeks after application.
If you follow these guidelines, you can enjoy a lush, green lawn without the hassle of pulling weeds all summer. Preen is a reliable product that does exactly what it promises. It prevents weeds without harming your grass.
So go ahead and use Preen with confidence. Your grass is safe. Your weeds are not. And your weekends can be spent enjoying your lawn instead of working on it.