Peat moss is considered by many gardeners to be one of the most useful materials to add to a garden. If you’ve done much gardening at all, you’ve probably either heard of peat moss or used it without realizing.
Many seed starting and potting mixes have peat moss as an ingredient. You’ll also find it in big square bales for sale at your local garden center.
If you haven’t yet used this much-loved garden ingredient, you might be wondering: What is peat moss good for? Here’s more about peat moss, the pros and cons of using it, and when to use it in your garden.
What Is Peat Moss?
Peat moss is dead plant material that originates in peat bogs. It forms when layers of mosses and other organic materials decompose beneath the surface of bog water.
This makes peat moss a very unique garden material because it forms without the presence of oxygen. (Compost, for example, is broken down in the presence of oxygen and other elements.)
The decomposition process takes place over a long period of time: thousands of years, in fact. Eventually, all that decomposing plant material breaks down enough to form a soil known as peat.
Once it has reached a certain stage, the peat is harvested and dried out. It’s then formed into bales, which is the end product you see in gardening stores.
Peat moss is harvested from bogs like this one. The moss decomposes underwater without the presence of oxygen to form a unique material with many garden applications.
Most of the peat moss used and sold in the U.S. comes from bogs in Canada. A small fraction of it comes from Michigan.
Around the world, the biggest peat bogs are in Russia, Ireland, Scotland, Finland, Germany, and Sweden. However, due to the concerns of many countries about over-harvesting, the actual peat supply comes mostly from Russia and Canada.
Types of Peat Moss
There will always be slight variabilities in peat moss based on where it was harvested from and what the unique conditions of the bog were.
However, there are two main types of peat:
- Sphagnum peat moss– This is the most commonly used type of peat moss in gardening and what you will most likely find if you look for it at a garden center. Sphagnum moss is what grows at the surface of bogs. It breaks down to form peat soil that is easier to harvest and less decomposed than what would be found deeper in the bogs.After it’s harvested and dried, sphagnum peat moss is light in color and can retain 10-12 times its own weight in water. Don’t confuse sphagnum peat moss with sphagnum moss (although their names are very similar). Sphagnum moss refers to the plant material harvested when it’s still alive and growing above water. The end product is a light, fibrous material that’s often used to decoratively line wire baskets.
Although it has a similar name, sphagnum moss is much different than peat moss. It isn’t decomposed and is made up of long, fibrous strands. It’s often used to line hanging baskets like this one.
- Black peat moss– Although technically a type of sphagnum, black peat usually refers to older, more decomposed peat moss that is darker in color when dried. For garden use, the peat is allowed to freeze when wet to improve its water retention. However, it still only retains water at 4 times its own weight.The final product usually ends up being dark brown in color (rather than black) and with much finer particles than sphagnum. Black peat is most frequently used by commercial growers like mushroom producers in blends, rather than by the home gardener.
Besides types, there are also different grades available based on how fine or rough the particle sizes are. Horticulture grade (also called medium/coarse grade) is the most popular choice and what you’ll most often find for sale.
Coarse/chunk grade is another kind used by growers, mainly for camellias, bulbs, orchids, and for making well-aerated mixes for large containers.
Pros and Cons of Peat Moss
Before we get into the ways you can use peat moss in your garden, let’s take a look at why gardeners love it so much and what its drawbacks are.
- Water retention– One of the most sought after characteristics of peat moss is its ability to retain moisture and release it to plant roots. It holds water much better than normal soils, compost, and many other growing mediums. Even better, instead of getting soggy and causing root rot, peat moss is able to release water as needed to plants as long as it’s not completely saturated.
- Texture– Another great aspect of peat moss is the aeration it brings to soil and the fact that it doesn’t compact. Most soils compact easily, especially when walked on or after something like tilling disrupts the soil structure. (That’s why no dig gardening is a better option.) Compaction isn’t good for your plants because it hinders water and nutrient absorption. Peat moss, on the other hand, stays springy even when wet and won’t get compacted.
Peat moss can retain about 10x its weight in water. It then releases the water to plant roots as needed. This means less watering for you, saving you time, effort, and money.
- Sterile medium– A sterile growing medium is one that’s free of pathogens, insects, and weed seeds. Not all bacteria and microbes are bad, but using a sterile medium is preferable at times. For example, seedlings are most at risk for getting killed by pathogens because they’re so small. That’s why most growers use a sterile mix for starting seeds.
- Acidity– Sphagnum peat moss ranges from slightly acidic to a pH around 4.4. This makes it an ideal medium for acid-loving plants.
- Low fertility– Peat moss is excellent at holding nutrients in the soil, but it doesn’t have much nutrient value on its own. At best, it will have trace nutrients, so it’s not a good choice for feeding your plants.
- Cost– For small applications, the cost of peat moss isn’t likely to dent your wallet very much. However, any large scale use of it (like amending a whole garden area) can get pretty expensive.
- Acidity– You’ve probably noticed that this is listed in the ‘pros’ section as well. That’s because the acidity of peat moss can be either a positive or a negative depending on what you’re using it for. In this case, if you grow plants that need a neutral or alkaline soil, the acidity of peat moss is a drawback.
- Nonrenewable resource– The biggest drawback by far of using peat moss is that it’s considered a nonrenewable resource. Technically, peat bogs do grow back but at a rate that can be as low as 1/16th of an inch per year.Canada is the only country that has taken steps as a peat moss supplier to conserve peat bogs. They allow only about .02% of their supply to be harvested every year. Other countries, like Scotland, have designated most or all of their peat bogs as protected and not to be harvested.
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- Environmental concerns– The actual harvesting process for peat moss is also under scrutiny. The bogs are drained of surface water, and layers of native vegetation are removed to get at the peat. Once it dries out enough, peat moss is essentially vacuumed up at rates of about 100 acres per day.
The main environmental concerns are habitat destruction for animals and plants living in the bog (including unique species of frogs and vegetation) and upset of delicate ecosystem balance. Once again, Canada has done the best job of finding more sustainable harvesting methods and working for bog restoration.
What is Peat Moss Good For?
Most gardeners agree that there is nothing quite like peat moss when it comes to certain garden uses. Here are the top ways to consider using it in your garden.
Make Your Soil More Acidic
There are other ways to lower the pH of your soil, but they either take much longer (elemental sulfur) or can lead to a buildup of heavy metals in your soil (iron sulfate).
Adding peat moss into the soil where you’re planting will immediately lower the pH. Even better, one application of it will last for several years, and it’s easy to reapply.
Hydrangeas need acidic soil to produce blue flowers. Alkaline soils will turn flowers pink. If you have a hydrangea bush that you want to be blue, peat moss is an easy soil amendment to increase acidity.
To make your soil more acidic with peat moss, spread out a 2-3 inch layer of it over the soil area where you’ll be planting. Then, work it down into the soil with a shovel or garden fork to a depth of about 12 inches.
Make sure you water the peat moss thoroughly until it looks and feels wet. Dry peat moss will end up taking moisture away from your plants, but it will retain water for a long time once wet.
Seed Starting Mix
Because it’s sterile and absorbent, peat moss makes a great ingredient in any seed starting mix. You’ll find it in many commercial seed mixes, and you can also use it to make your own mix.
You shouldn’t use peat moss alone as a seed starter. Start with it as your base ingredient and add an aerating ingredient like perlite or vermiculite. You can also add a tiny amount of fertilizer to feed your seedlings once they start growing.
Other optional ingredients include lime (to balance out the pH), coconut coir, and beneficial mycorrhizae (helps your plants to root).
One question many beginner gardeners have is what’s the difference between seed starting mix and potting soil?
Peat moss is a common base ingredient in both seed starting mixes and potting soil. You can easily make your own mixes by adding other ingredients like perlite, vermiculite, compost, fertilizer, etc.
Seed starter mixes are usually more lightweight than potting soil and have low to no nutrients. They are optimized to get your seeds started and allow your seedlings to easily put down roots. Most seed mixes are sterile to prevent bacteria and other pathogens from killing your seedlings.
Potting mixes are usually heavier and more fertile because they are designed to support larger, growing plants. They can be sterile but many aren’t.
Peat moss makes a great addition to store-bought and DIY potting soil. It helps soil hold onto moisture for longer, which is especially great for container gardens, while still keeping the soil well-drained and aerated.
It also holds onto nutrients that might otherwise be washed out of containers when you water your plants.
Use peat moss as ⅓ – ⅔ of your total potting soil mix. The rest can be mainly compost or store-bought soil with perlite and some type of fertilizer added in. If you are growing plants that need a neutral to alkaline pH, add in some lime to balance out the peat moss.
Amend Your Garden Soil
Peat moss has characteristics that make it excellent at amending both heavy clay and sandy soils.
If you’re trying to grow in either heavy clay or sandy soil, peat moss is one possible amendment to improve soil texture and drainage. Keep in mind that many vegetables and common garden plants prefer a neutral or slightly alkaline soil, so you may need to balance out the pH with lime.
The light, aerated texture of peat moss will help to lighten clay soils. It’s especially useful for amending clay soils that have been compacted and can help to prevent compaction in the future.
Peat moss will also improve drainage, which is often a problem in clay soil.
For sandy soils, amending with peat moss will give your soil better water and nutrient retention. Nutrients tend to leach out of sandy soil, especially with lots of rainfall, and that’s something amending can fix.
To amend with peat moss, spread it out over the area you want to amend and work it in to a depth of 12 inches. If you don’t want to lower the pH of your soil, mix in limestone at the same time.
One of the more recent uses of peat moss in the garden is to make biodegradable pots for seed starting.
You can buy these pots online or at your local garden center. While most seeds are more easily started in flats or cell packs, plants that hate having their roots disturbed are best started by seed in these pots.
The pots get planted in the ground with your seedlings whenever it’s time to plant. They naturally degrade and break apart as time goes on, eventually becoming a part of the soil.
A few tips about peat pots will make your life a lot easier when using them.
Biodegradable peat pots were a great invention in the gardening world. They allow you to plant seedlings without disturbing their root systems, which is great for plants that don’t transplant well.
Before adding your seed starting mix to the pots, get them wet by soaking them in water for 1-2 minutes. When you water your seedlings after they sprout, water the pots at the same time to keep them from drying out because dry pots will wick water away from your plants.
When you go to plant the pots, break off the rim of each one so that it’s level with the soil your seedling is growing in. Make sure no part of the peat pot is sticking out of the soil after planting or it will act as a wick to take water away from plant roots.
Normally, you wouldn’t use peat moss as a mulch. Regular mulch is more cost effective, and it would be a waste to use something nonrenewable like peat moss on a large area.
However, you can mulch with it around your acid-loving plants (azaleas, rhododendrons, blueberries, cranberries, gooseberries, camellias, gardenias, magnolias).
Doing this will not only help to keep moisture in the soil and keep weeds down, it will also help to keep the pH from creeping back up over time. A nice mulch with peat moss every year or two will keep the acidity of your soil where you want it without much trouble.
Alternatives to Peat Moss
If you feel concerned about the environmental impact of harvesting peat moss, there are some alternatives out there, although none have exactly the same characteristics.
For certain applications, compost can be a good alternative to peat moss. You can easily make compost yourself by using bins like these ones, and there are also more compact options available for smaller spaces.
Here’s a look at the top three.
If you want to amend your soil without lowering pH, compost will almost always do the trick.
It’s easy to make compost at home, and it will give your soil better drainage and texture. Compost also provides a lot of nutrients to soil, something that peat moss doesn’t do.
An easy method for amending or fertilizing with compost is to apply it to your garden beds in late fall. The winter weather will help to break it down and incorporate it into your soil, saving you a lot of effort in the spring.
Keep in mind that this is not a good option if you want to acidify your soil, and it compacts much more easily than peat moss.
Coconut coir is a fairly new addition to the gardening world and is often marketed as an eco-friendly alternative to peat moss.
It retains water, lightens soils, and adds better drainage. You can use it in place of peat moss as part of a seed starting or potting mix. It’s also a very renewable resource since it comes from the husks of coconuts.
Coco coir comes from the husks of coconuts. It used to be a waste product that was discarded after the meat of the coconut was taken out, but it was discovered to have many useful attributes for gardening.
The downside is that coconut coir is just as or more expensive than peat moss, so it’s not cost effective for large projects. It also won’t change the pH of soil, which can either be a plus or a minus.
Biodegradable peat pots are a huge hit in the gardening industry. However, some companies are coming up biodegradable options that aren’t made out of peat.
One of the most prominent options so far is called CowPots. They are made from composted cow manure and are completely biodegradable and renewable, plus odor-free!
CowPots may cost you a little more than peat pots, but that little bit extra is worth it for many gardeners.
Using Peat Moss Sustainably
Peat moss remains a unique gardening material with characteristics that no other medium has. In many situations, there’s just no substitute for it.
In your own garden, the best way to use peat moss sustainably is to reserve it for applications where there is no good alternative and to use it only for small scale projects as much as possible.
If you have a bag of peat moss on hand, why not use it to make your own seed mix or to try growing acid-loving gardenias indoors?
Jen is a master gardener, interior designer and home improvement expert. She has completed many home improvement, decor and remodeling projects with her family over the past 10 years on their 4,500 sf Victorian house. She is also a passionate farmer who keeps goats, chickens, turkeys cows and pigs on her farm, and an instructor for her community’s Organic and Sustainable Farming project.