If you need to re-seed a lawn, whether you’re starting from scratch or repairing a lawn after major damage, you have likely come across advice that tells you to cover the grass seed with either peat moss or straw. Between these two options, there is a superior choice.
Peat Moss or Straw for Grass Seed – The Short Answer
If you can get it, straw is the best choice if you’re comparing straw vs peat moss alone. There are half a dozen options that are better than peat moss if you can’t find straw. There are, however, some circumstances in which peat moss is a choice you may need- if you have certain problems that only peat moss can solve such as severe compaction or moisture retention issues or an unreasonable alkaline pH.
Peat Moss Vs. Straw for New Grass Seed: Which is Better?
New grass seeds should be scattered evenly over loose soil and covered with dry, untreated straw lain down in an even layer no thicker than 1”. Straw is cheaper and more widely available than peat moss and it will provide a small nutrient boost over time without altering the composition of the soil a great deal. For most new lawns, this is the ideal option. However, peat moss should be used in special cases or when no alternative is available.
The Pros and Cons of Using Peat Moss for Grass Seed
Peat moss, just like any soil amendment or seed cover, comes with several important advantages as well as disadvantages. Below you can see the most important reasons why peat moss could be the best choice for seed germination- or not.
Pros of Using Peat Moss for Grass Seed Germination
There are 3 main pros when it comes to choosing peat moss for grass seed germination.
Sterility
Peat moss is often sold sterilized. This means no weed seeds, spores, or diseases will be shipped with it. Straw can also be sold sterilized, but this is rare and often makes it much more costly. With peat moss, this is almost a given- especially if the peat in question was imported.
Water Retention
Peat moss retains more moisture, ounce for ounce, than straw will. This is great news for seed germination and many types of sprouts, as long as they aren’t susceptible to root rot or damping off.
Weight and Loft
Peat moss, when dehydrated as it often is for shipping and storage, is very light. This can make it easier to purchase and transport large volumes of compressed peat. If you’re seeding a lawn on your own, a lighter medium can make all the difference between success and frustration.
Cons of Using Peat Moss for Grass Seed Germination
There are several reasons why peat moss doesn’t make the best germination medium or cover for grass seed.
Hydrophobic Soil
Though peat moss is great at retaining water, it can quickly become hydrophobic if it piles up in a thick layer and is allowed to dry out completely.
Erosion and Wind
Peat moss is a light, fluffy substance. When it’s dry it can easily be blown away. If the peat moss was dry before a sudden downpour, it’s also susceptible to sudden erosion or being washed away, especially if the lawn being seeded is uneven.
Soil Acidity
In some circumstances, you may have soil that will not retain moisture on its own without significant amendment. This may mean you have already used peat moss in your lawn’s soil. If this is the case, using it to cover the grass seed as well may result in a significant change in pH. In a case like this, a combination of sawdust or small-particle wood chips and perlite could be the optimal addition to your grass seed. Both of these substances can help your lawn and soil retain more moisture than straw but without the side effects of peat moss.
Untreated peat moss will acidify your soil – this is not a myth. If it’s just used in an even layer about 1/4″ thick or if it’s scattered with the seed to promote an even spread, this change may be as little as .5. For example, it may change the pH from a neutral 7 to a slightly acidic 6.5.
However, if you work the peat moss into the soil, use it for scattering, and use it as a cover as some experts or even the peat moss packaging may advise, you could be looking at a change of 1.5 levels for untreated peat. That can reduce germination rates for some grass seed varieties and harm the outcome for any germinated seedlings.
The Greater Costs and Risks of Using Peat Moss
Peat bogs are mined. This means that the peat is removed and unlikely to regrow as quickly as it would need to for it to be a sustainable resource. Once a peat bog has been stripped, it will not recover without intervention. This means wildlife habitat is lost as well as an important piece of the ecosystem that may affect local water levels and more.
In the UK, there are plans in the works to ban the use of peat moss both for home gardeners in the short term and commercially in the long term. Similar plans are being considered in Canada, one of the greatest suppliers of peat moss. With this being the case, relying on peat or making it part of your lawn or garden strategy may not be the best strategy for the near or far future.
The Pros and Cons of Using Straw for Grass Seed
Straw, like peat moss, has an assortment of strong reasons why it makes a decent cover for grass seed as well as a few things that may make you want to pass it over for another option.
Pros of Using Straw for Grass Seed Germination
Straw comes with many benefits for your grass seed now and in the future. These benefits can take time to fully reveal themselves in nature, but you can find a list of what you should expect below.
Soil Composition
Soil composition is the key factor to consider before adding a layer of anything. However, when it comes to the binary choice of straw or peat moss, straw is less likely to disrupt the balance you have already created as, when decomposed, it will add to the organic matter or loam layer. If, however, you need the loft or moisture retention of something like peat, you may want to look at alternatives to straw for your grass seed like coconut coir, sawdust, or even germination mats as these are all pH neutral and are unlikely to change the texture or the soil much.
It’s also important to keep in mind that as the loam layer of your soil increases, so does its ability to retain moisture over time without further additions or frequent aeration. Though it will work more slowly than peat, straw can help this situation in a sustainable way for most soil compositions, except hard clay.
Staying Power and Erosion Prevention
Straw is less likely to wash or blow away than peat moss is. Straw is excellent for use on hills and can help keep the grass seed and nutrients you have applied right where they are for months after application.
Moisture Retention
Though the effect isn’t as strong as it would be with peat moss, straw can still help retain moisture around grass seeds and seedlings. While peat moss acts like a sponge around the grass seeds, the straw will act more like a lid above them, keeping moisture beneath it and slowing down local evaporation.
Cons of Using Straw for Grass Seed Germination
When compared to peat, there aren’t a lot of cons to using straw that stand out. However, there is one con that could be a make-or-break factor if you’re strongly considering straw as the cover for your grass seed.
Lack of Sterility
There is potentially one big con to using straw as a cover for grass seed – the potential it has to transmit weed seeds to your property. While peat moss is typically sold sterile, straw is not. It can be, but often it is sold from a local field and may not be subject to strict testing.
Straw vs. Peat Moss: Why Straw is the Best Choice
If the choice is between peat moss or straw for soil amendment or seed germination, the best choice should be clear. Straw can keep grass seed in place and discourage foraging animals while improving soil texture, nutrient content, and moisture retention. It will not alter the pH of the soil and it can help prevent soil erosion in the short term. Unless you have pure, hard clay soil or a problem with alkaline soil, straw is the better choice when it comes to straw vs peat moss for grass seed.
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