When starting a new lawn from scratch, you could just broadcast some grass seed and hope that it grows, but the resulting lawn will be patchy at best, dismal at worst. Grass seed needs to be kept moist for as long as two weeks, and while you can valiantly run out to water every few hours, you can save yourself the trouble and grow yourself a fabulously thick lawn by covering new grass with a light mulch.
You can cover new grass seed with a 1/8-inch layer of organic compost, high-quality topsoil, lawn clippings, organic straw, bagged paper mulch, or seed starting mats. By covering grass seed, you improve germination rates, reduce the need for watering, improve root development, prevent erosion, and hide grass seed from birds.
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Do I even need to cover new grass seed at all?
You don’t need to cover new grass seed, but if you’re starting a new lawn from bare dirt or filling in a new patch, then covering new grass seed will significantly increase your success rate. Covering grass seed will:
- Improve germination rates by keeping grass seed moist. It takes between 7 and 14 days for grass seed to germinate, and grass seed (like all seeds) needs to be kept moist for the entire time. If you don’t cover the seed with a light layer of mulch, the seed will keep drying out — and you’ll have to keep running out to water it. Without proper moisture, your efforts will be patchy or time-consuming at best, or a waste of money and grass seed at worst.
- Improve root development. Lack of moisture also means that grass seed that do germinate will struggle to establish their roots and will grow slowly. Healthy grass needs deep roots to endure scorching summer heat, regular mowing, and foot traffic. Shallow roots grow along the first couple inches of soil, which quickly dries out and will need more frequent watering.
- Hide grass seed from birds and other seed-eaters. Grass seed just laying on bare dirt is like laying out a banquet for birds, squirrels, and everything else that would love to gobble up your grass seed. A layer of mulch will hide a lot of the grass seed from easy reach, so most of the grass seed you lay down will end up becoming your lawn and not a bird’s dinner.
- Prevent erosion. But birds aren’t the only reason your uncovered grass seed may disappear. Again, it takes weeks for grass seed to germinate and establish itself. Heavy winds or hard rains can easily wash away grass seed. Mulch prevents erosion, meaning that your hard work won’t wash away.
If you’re overseeding your existing lawn, you don’t need to cover new grass seed as the existing grass will provide much of the same protection as mulch.
What is the best thing to cover new grass seed?
The best thing to cover new grass seed with is a ¼-inch or less of compost. Compost is great at retaining moisture, and it also improves your lawn soil by feeding the beneficial microbes and insects that aid your grass against pests and disease, helps aerate the lawn (less compaction), and provides the needed nutrient boost for growing strong grass seed starts. Once applied, you don’t need to remove it as the grass will grow above it and the compost will break down completely.
Compost is also really easy to apply, even without special equipment. You can apply it with a rolling compost spreader, the same broadcast spreader you used to spread the seed, or even just broadcast it with your hand or a shovel. You should still be able to see 10% of the grass seed through the compost. If you can’t, it’s too thick and will smother the grass.
Is hay or straw safe to put on my lawn?
Hay and straw that haven’t been sprayed with persistent synthetic herbicides are safe to put on your lawn. Hay contains seeds that can sprout, considering that you’re using the hay to create the perfect germination conditions, causing weed issues. But persistent herbicides like picloram and clopyralid can persist on hay and straw for four years after it’s been applied, which can end up poisoning other garden plants.
It’s best to avoid hay and straw that you don’t know the origins or the herbicide history of. Go for organic straw and hay (particularly when you can meet the farmer who grew it), or use one of the many other effective mulching options like organic compost.
What can I put on new grass seed instead of straw?
Instead of straw, you can cover grass seed with:
- Organic compost. A 1/8-inch layer of compost is usually the best option, as not only is compost great at absorbing and keeping moisture, it’ll also improve your soil and feed your lawn! You can make your own, or buy it bagged or in bulk. Organic is best to avoid herbicide drift.
- You can also use topsoil much like compost, but it won’t provide any additional nutrition. This is a great option, though, if you have any leftover high-grade topsoil from other projects, and don’t have a dependable source of compost.
- Bagged grass seed mulch. Lawn care manufacturers also offer their own manufactured seed mulch that will biodegrade, although they will often contain synthetic fertilizers. If you’re growing a natural lawn, compost, and lawn clippings are better bets.
- Lawn clippings. Lawn clippings are actually quite similar to straw and hay. It is, after all, cut grass. But it’s free and you know exactly what herbicides (if any) have been applied to it. Just make sure to spread out any clumps when applying it to your grass seed, or it’ll prevent the seed from germinating.
- Seed mats. Seed mats are manufactured out of natural materials (like wood fibers) that you simply roll out taut over new grass seed. They’re more expensive, but especially useful for starting seed on hills and slopes.
Improve your lawn starting efforts with a thin layer of mulch. Just a 1/8-inch will help retain moisture in between watering, improve root development, prevent erosion, and even hide the grass seed from birds. (Feed the birds with bird seed, not the more expensive grass seed.) Organic or homemade finished compost works best as it’ll also improve your soil by aerating it and feeding the microbiology, as well as feeding your lawn for the rest of the year.
Trying to grow a new lawn on hard-packed earth? We’ve got a guide for that!
Jamie is the founder of The Backyard Pros. When he was 15 years old he started working at a garden centre helping people buy plants, gardening products, and lawn care products. He has real estate experience and he is a home owner. Jamie loves backyard projects, refinishing furniture, and enjoys sharing his knowledge online.