Peat Moss vs. Coco Coir: Differences, pH and Which to Use

Peat Moss vs. Coco Coir at a Glance

Peat moss and coco coir do the same job in a potting mix: both are light, spongy, low-nutrient materials that hold water and air around roots. The main differences are pH and rewetting. Sphagnum peat moss is strongly acidic at pH 3.0 to 4.5 and repels water once it dries. Coco coir sits near pH 6, takes water back up easily, and lasts longer in the pot, but it can carry salts if it was not washed.

	Sphagnum peat moss	Coco coir
Source	Partly decomposed moss from bogs, mostly Canadian	Milled coconut husk, a by-product of the coconut industry
pH	3.0 to 4.5	5.8 to 6.9
Water held, by volume	60 to 68 percent	73 to 80 percent
Air space after draining	10 to 15 percent	9.5 to 12.5 percent
When it dries out	Repels water and shrinks from the pot wall	Rewets readily
Nutrient holding (CEC)	90 to 140 meq/100 g	39 to 60 meq/100 g
Salt risk	Low	Sodium and chloride if unwashed
Lime needed	Yes, for most plants	Less than peat
Renewal	About 1 mm of new peat a year	Several coconut crops a year

The physical numbers come from the University of Arkansas greenhouse program and are closer than most gardeners expect. Coir holds somewhat more water per pot and the air space ranges overlap, so neither figure decides the question by itself. The RHS gives a wider air range for coir, 10 to 20 percent, depending on how coarse the grade is.

Is Coco Coir the Same as Peat Moss?

No. They look alike in the bag and are unrelated. Sphagnum peat moss is the dead, partly decomposed material that builds up in the lower levels of a peat bog. Purdue Extension notes that most of it is harvested from bogs in Canada.

Coir is a by-product of the coconut industry. Processors mill the husk, screen the fibers to less than 2 centimeters, air dry them, and compress the result three to four times over into bricks, blocks or bales. The brick expands again when you soak it. Neither material supplies meaningful nutrients, so a mix built on either one needs fertilizer or compost.

Coco Peat vs. Coco Coir vs. Sphagnum Moss

The names cause much of the confusion. Coco peat, coir pith and coir dust all describe the same thing: the fine, soil-like grade of coir, which is what goes into seed-starting and potting mixes. Coco coir is the broader term. It also covers the long fibers and the husk chips, which hold water while leaving air pockets in a container mix. A bag labeled coco peat contains no peat.

Sphagnum moss and sphagnum peat moss are also two products. Iowa State University Extension puts it this way: sphagnum moss is the living moss that grows on top of the bog, and peat moss is what accumulates below it. Dried sphagnum moss is used to line hanging baskets and make wreaths. It is a liner and a wrap, while peat moss and coir are mix ingredients. For lining a basket, long-fiber sphagnum moss and coir fiber mats are the two options. For filling it, choose between peat moss and coir pith.

pH: The Biggest Difference

Unamended sphagnum peat has a pH of 3.0 to 4.5. Most container crops grow best between 5.4 and 6.6, so peat-based potting mixes are sold with limestone already blended in. Clemson’s potting mix recipe, for example, is adjusted to about pH 6.0 with dolomitic limestone. If you buy a plain bale to make your own mix, you have to add the lime yourself.

That acidity helps with acid-loving plants. Blueberries, azaleas and rhododendrons want soil well below what vegetables prefer, and a peat-heavy mix helps get them there. Our guide to growing blueberries in pots uses peat for that reason.

Coir runs from pH 5.8 to 6.9 in the Arkansas figures, and the Royal Horticultural Society gives 5.5 to 6.2. Either way it lands in the range tomatoes, peppers, herbs and annual flowers want, and Purdue notes that it needs less limestone than peat.

Water Holding and Rewetting

Both hold a great deal of water. Peat moss absorbs 10 to 20 times its dry weight, and the RHS puts coir at 10 times its dry weight. By volume, coir holds 73 to 80 percent water against 60 to 68 percent for peat.

The practical difference shows up after a missed watering. Peat is naturally hydrophobic when dry, which is why commercial peat mixes include a wetting agent. A dried-out peat mix also shrinks and pulls away from the container wall. Water then runs down the gap and out the drainage holes while the root ball stays dry. Our article on container plants drying out fast explains how to rescue a pot in that state.

Coir is hydrophilic. Water spreads evenly over the surfaces of the fibers, so a coir mix forgives hanging baskets, small pots and vacation weeks.

Salts and Feeding in Coir

Coir’s weak point is chemistry. Coir that was not soaked and rinsed during processing can contain excess potassium, sodium and chloride, and the electrical conductivity of raw coir ranges from 0.3 to 2.9 mmho/cm. Most coir sold for gardening has been washed in plain water, and a smaller share is buffered with calcium nitrate. Clemson’s advice for anything not labeled washed is to rinse it thoroughly before use.

Coir also changes what plants need from fertilizer. Purdue reports that coir-based mixes require more calcium, sulfur, copper and iron than peat mixes, and less potassium. They can also tie up more nitrogen. For home growers that translates to feeding from the start with a complete fertilizer that lists calcium, and watching seedlings for pale new growth.

Peat holds onto nutrients more strongly, with a cation exchange capacity of 90 to 140 meq/100 g against 39 to 60 for coir. A peat mix therefore buffers a little better against missed feedings.

How Long Each One Lasts

Coir breaks down slowly because of its high lignin content. The RHS notes that commercial growers keep blueberries in coir for up to 10 years. Peat decomposes relatively slowly too, but peat mixes shrink as they age and dry. For a shrub, a dwarf fruit tree or a houseplant that will stay in the same pot for several seasons, coir or a coir and bark blend keeps its air space longer.

Sustainability

Peat forms at about 1 millimeter a year, so 1 meter of peat represents roughly 1,000 years of growth. Peatlands cover only 3 percent of the world’s land area and store more than twice the carbon held in all the world’s forests. Draining and cutting a bog exposes the peat to oxygen and releases that carbon. Oregon State University Extension reports that a replanted bog can take 30 to 40 years before it stops releasing carbon.

Coir is a by-product of a food crop, and coconut palms produce several crops a year. Its costs are the fresh water used for washing and the fossil fuel used for shipping. Washington State University Extension points out that peat sold in the United States travels a shorter distance from Canada, mostly by truck, while coir travels farther by sea. Neither is free of impact. Of the two, coir is the renewable one.

Coco Coir or Peat Moss: Which Should You Use?

Choose by plant and by watering habits. Peat is the better base for acid-loving plants, where its pH of 3.0 to 4.5 does useful work. Coir is the better base for pots that often dry out, for plants that will sit in one container for years, and for home mixes made with no lime on hand. Gardeners who want to avoid peat for the sake of the bogs should look for washed coir or a peat-free blend.

For everything in between, such as seed starting and a season of container vegetables, both work. A standard peat recipe from Purdue is 2 parts sphagnum peat moss, 1 part perlite and 1 part vermiculite, with lime added. Coir pith can stand in for the peat if you leave out the lime and start feeding earlier. University of Maryland Extension suggests stretching any soilless mix by blending 1 part compost with 2 parts mix, which adds nutrients that neither base supplies.

The other ingredients matter as much as the base. See perlite versus vermiculite for the mineral half of the recipe and the best potting mix for containers for ready-made options.