Coir - yes or no?

How coir is used in gardening

Besides being used as a liner for hanging baskets, coir's most common use is as potting soil or an ingredient of potting mixes. For most seeds, it is recommended the mix contain no more than 40 percent coir.

Most potting mixes still use peat, but you can mix up your potting mix blend quite easily. Since coir is organic and sterile, it's an excellent choice for starting seeds.

Coir is also used as a soil amendment. It improves the air porosity of soils, even when wet, and aids in moisture retention. Coir absorbs 30 percent more water than peat and is much easier to re-wet, when dry.

Advantages of using coir over peat

Peat takes hundreds of years to form, and although many reputable firms in the peat industry are trying to harvest and manage peat in a responsible, sustainable rate, demand is so high, we need to look at alternative substances. Since coconuts will continue growing throughout the year and can be harvested every two months, they fit the sustainability requirement. It's a bonus that they are a byproduct that was going to be wasted. Using it as a soil amendment solves two dilemmas.

There are additional advantages to coir:

• Coir is slower to decompose, so it lasts longer in the soil.
• It is both sterile and free of weed seeds.
• It has a less acidic soil pH, generally in the 5.8 to 6.8 range. (Peat is in the 3.5 to 4.5 range.)
• Coir improves air porosity in soils, even when wet, as well as improving moisture retention.
• It is easier to re-wet, when it dries out, helping plants recover from dry conditions quicker and requiring less irrigation.
• Studies indicate coir may provide some resistance to pythium and other root diseases.

Disadvantages of using coir

Coir does have some downsides:

• Coir tends to compact, which will come as no surprise to anyone who has handled a coir brick.
• Because it retains water, there is a chance of salt buildup.
• Like peat, it has negligible amounts of calcium, but since coir's pH is already neutral, you don't want to add lime.
• It doesn't have much in the way of other nutrients either, although it is fairly rich in potassium and a handful of micronutrients.
• Coir is more expensive than peat.