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Mike McGrath

What Is Peat Moss and How to Use It


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Look in gardening sheds across the country, and you'll likely find peat moss. For decades, gardeners have used this soil amendment for seed starting, improving the soil and for creating potting mixes. In recent years, there's been some environmental concerns about using peat moss because it's not a sustainable resource. This blog explores what peat moss is and the best uses for it in the garden.

What Is Peat Moss?

Peat is dead material that has been submerged in bogs for thousands of years. Most peat moss used in the United States comes from peat bogs in Canada. Because peat forms so slowly (often taking 20 years to form 1 inch of peat), it is not considered a renewable resource.

In Canada, the harvesting of peat moss is highly regulated. When harvested, the bog is drained and vacuum harvesters take a layer of peat moss that is about 2-3 inches thick.

Peat moss is often sold in plastic-wrapped bales in garden stores. The material is very dry, lightweight and dusty. Because it is sterilized and doesn't have any bacteria, fungus or weed seeds, it's a favorite for using for seed starting.

What Is Peat Moss Used For?

Because peat moss is lightweight, moisture retentive, doesn't compact, is readily available and is acidic, it has many uses in the garden. It's often used with acid-loving plants, like blueberriesWhile peat moss, unlike compost, and peat moss is good for growing tomatoes (both seed starting and mixing into the soil to moderate moisture). Because of its composition, peat moss is often mixed with clay soils to improve their drainage and reduce compaction. Its sterile, moisture retentive qualities make it a favorite for seed-starting too.

How to Use Peat Moss

Here are some of the most common ways that peat moss is used in gardening.

  • Soil Amendment

    While peat moss, unlike compost, doesn't have lots of nutrients, it can improve the soil structure. For example, when mixed into clay soil, it improves aeration and drainage. For fast-draining soils, it can be used to improve water retention. Because it is sterile, peat moss does not introduce pathogens into the soil. When used as a soil amendment, use two parts soil to one part peat moss.
  • Seed Starting

    Its sterile and lightweight qualities make it a favorite for seed starting too. Seeds started in a peat moss mix are less likely to rot--and when they germinate, they have an easier time pushing through the lightweight peat moss. It's also free of weeds. Usually peat moss is mixed with other growing media like perlite, vermiculite or coir.
  • Hydroponic Growing

    When mixed with other growing media such as perlite or vermiculite, it creates a nice balance of moisture and aeration for hydroponic growing.
  • Growing Acid-loving Plants

    Peat moss is acidic, and is excellent for use with acid-loving plants, like blueberries, azaleas and tomatoes. Because it can make your soil more acidic, you may need to add lime to the soil.

The Difference Between Peat Moss & Sphagnum Moss

Sometimes people confuse peat moss with sphagnum moss. While they are both found in garden stores, they are different and have different uses in the garden. Peat moss is not living and is sterile. Sphagnum moss is a living (or recently living) plant. Sphagnum moss is commonly used to line wire plant baskets. Appearance-wise, peat moss look more like dirt while sphagnum moss looks like a plant.

The Benefits of Using Peat Moss

Peat moss is a favorite among gardeners because of its beneficial properties, including:

  • Cleanliness: When you spill peat moss, you don't make much of a mess. Just sweep up the dry material. No dirty streaks are left behind.
  • Moisture retention: Peat moss retains moisture. This makes it useful for seed starting. When mixed into garden soil, it helps the soil retain moisture. For plants like tomatoes, a regulated water supply produces better fruits.
  • Disease prevention: Peat moss is sterile, so it doesn't introduce diseases and pathogens to the soil or potting mixes.
  • Doesn't compact: Peat moss doesn't compact, making it an excellent choice for mixing into clay and compacted soils. Soil mixed with peat moss has a bit of a spring to it.
  • Availability: Most garden stores sell peat moss, and it's easy to buy a bale and transport it home.

The Downside of Using Peat Moss

  • Few nutrients: Unlike compost, peat moss has few nutrients, so you may have to consider using fertilizer.
  • Dryness: Peat moss can be dusty to work with.
  • pH Levels: Peat moss is very acidic, with often a pH of 3-4.5.
  • Non-renewable: Because peat moss forms so slowly, it is considered a non-renewable resource.
  • Expensive: It can be an expensive soil additive. Many gardeners find compost less expensive, especially when they can make their own.
Mike McGrath

Expert Advice

Question. Dear Mike: How do you feel about using peat moss as a mulch? And is there a rosebush without thorns? Thanks!

    ---Hank in Wilmington, Delaware
Answer. Not completely without thorns, Hank; but some rose varieties are said to have very few, including the legendary "Climbing Cecile Brunner", a light pink, repeat blooming old garden rose. The noted German breeder Kordes has a dozen 'thorn-less' varieties in their "Satin Touch" line; and another dozen are available under the "Smooth Touch" brand from Australia—all of which have the word Smooth in their name (like me).

Anyway, don't use peat moss to mulch them roses. Yes, the low price per cubic foot of material makes using the contents of those giant bales for mulch an attractive thought. And yes, mulching is listed as a potential use on some of the wrappers. (Heck—the big bale I have out back says you can use it as a breakfast cereal in a pinch.) But peat moss is not the wisest choice for a mulch.

First and most important, peat moss is highly acidic, and using it as a mulch around non-acid loving plants could greatly stress them. It also has a tendency to form unsightly surface cracks when it dries out; and it's too light to stay in place when faced with high winds and rains. (In fact, its so naturally dry and dusty it would be difficult to apply as a mulch on anything other than a 100% wind-free day.) And it doesn't convey much (or any) actual nutrition to plants, the way other organic mulches do.

But I know where you're coming from; you get soooo much of it for so little money; and every garden center has it. Would that packaged compost were so common! Anyway, stick with the good mulches: Compost, pine straw, dried clippings from herbicide-free lawns, shredded fall leaves and cocoa bean and other seed and nut hulls and shells.

And of course, stay away from wood, bark, root and rubber mulches. I'd go for peat moss neutralized with some wood ash or lime before I'd use any of those bad boys.

Question. Mike: What is your opinion on using peat moss as a soil amendment? I have read conflicting stories. Also, can it be composted with my shredded leaves and grass?

    ---Lisa in Dothan, AL
Answer. It can be very useful, Lisa. But as we just warned Hank The Rose Thorn Scaredy-Cat, you have to know what you're doing. You don't want to mix lots of peat moss into your soil willy-nilly any more than wood ash. Because just as the wood ash can make your soil too alkaline, peat moss can make it too acidic; especially if you live in an area where the soil is already acidic. We'll go into detail about using it safely in a minute.

READ COMPLETE ANSWER

Question. I'm writing this as I get ready to plant my tomatoes, eggplants and peppers, and I wonder if the addition of peat moss to my soil would change the pH in a detrimental way. I have spent the past three years conditioning the soil with compost, but the dirt doesn't seem to be deep enough yet. Would the addition of peat help or hurt? Thanks,

    ---Danielle in Butler, TN
Answer. Alone and un-amended, it could well hurt, Danielle. Have a soil test done. If, like our friends in Oklahoma and the Far West, your soil is naturally alkaline, adding peat moss would both bulk up your beds and improve the pH. But if your soil is already acidic (as it is for most of us in the North), it would be a very bad idea.

If you have a lot of peat moss handy, consider following Mel Bartholomew's Square Foot Garden Plan. Create raised beds and fill them with lots of compost, peat, perlite and vermiculite; essentially creating a giant outdoor container that drains exceptionally well and can support a lot of plants. If necessary, add some wood ash or lime to the mix to level out the pH. And wear a dust mask! All of those ingredients besides the compost are very dusty.

Question. A friend gave us several large bales of compressed peat moss and I am wondering what to do with it. What do you think? Thanks,

    ---Barb in Maple City, MI
Answer. I think it's time for me to finally answer this question, Barb! My favorite use is to spread some peat an inch or two thick around the base of my acid-loving plants like rhododendrons and azaleas, and then cover that with an inch of compost. It keeps their soil rich and acidic just the way they like it.

For blueberries, which require a HIGHLY acidic soil, I first plant the things in half compost/half peat moss (a pretty good replication of their natural habitat) and then mulch them with lots more peat moss covered with some compost every season.

I also use peat moss to make my pink hydrangeas turn blue. And I combine equal amounts of peat, perlite, vermiculite and compost to make a perfect container/seed-starting mix, always making sure to add some wood ash to counteract the acidity of the peat; a couple tablespoons of ash for a big container; about a quarter cup to sweeten up a wheelbarrow load.

Peat moss is a valuable garden amendment, but is a non-renewable resource. Because of these environmental concerns, many gardeners are using it a bit less or being selective in how they use it. It remains a favorite for seed-starting and for use with acid-loving plants, especially blueberries.



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