A few years ago, a hastily purchased bag of “expanding” potting soil introduced me to coir.

Distracted, I hadn’t paid attention to what I had, but when I added the required water, the soil did expand and became a fluffy, dark, beautiful mix.

I planted container tomatoes into it with excellent results. Wanting to know more, I started to look for more information about this fascinating product and for different ways to use it.

Soil amendment

A relative newcomer as a soil amendment in America, coir offers gardeners an alternative to peat in soil improvement.

  • Fibrous material in coconut shell husk
  • Previously considered a waste product, coir is the fibrous material found in the hard husk of a coconut shell. It’s processed, washed, and made into many different kinds of garden products, from basket liners and ivy posts to mulch and soil amendments.

  • Hydrated bricks, bales, pellets, dust
  • When you purchase coir, especially online, make sure it is from a reliable source and has been properly prepared. As a soil amendment, it can be bought already hydrated in bags or in compressed and dried form: bricks, bales, pellets, or dust. Bricks, bales and pellets are the easiest to transport and take less room to store before use. It has to be hydrated before it is used.

  • Composition and dimensions
  • Compressed coir is very dense and is virtually impossible to cut or break in its dry state, so smaller bricks rather than bales might be advisable to start with.

    Coir can hold up to seven times its weight in water and will expand up to three to five times the size of the block, so make sure you use a container large enough when you wet it.

    A brick is usually about 1/3 cubic feet. A 5-gallon bucket should be large enough for the wet product. For a bale, (about 2 ½ cubic feet), use a trash can, a large wheel barrow or a large plastic storage container. The coir visibly expands and becomes dark and fluffy as it absorbs the water.

    As sections get wet, break them away so water can get to the rest of the block. Kids love this process. Water and magic.

    Coir vs. peat

    Coir wets more easily than peat and if it dries out, it rewets more readily. Once the coir is wet, it is ready to use, and whatever is unused can be stored in a covered container for years without loss of benefits.

  • Neutral in acidity; high in potassium
  • Unlike peat, which is acidic, coir has a pH of 6 to 6.7, so it is essentially neutral. It does not increase acidity in the soil. You might not want to use coir if you are planting acid-loving plants like blueberries, camellias or azaleas.

    Coir is high in potassium and provides trace elements of zinc, copper, manganese and iron. It may be necessary to add calcium at some point if you are growing tomatoes.

  • Resists compaction in soils
  • Added to the garden soil in similar proportions as peat, coir improves the structure of sandy soils, encouraging moisture retention, and breaks up heavy clay. It resists compaction better than peat, encouraging root growth and keeping moisture and nutrients available to the plant, but at the same time allowing for good drainage. It provides a sturdy, stable foundation for plant growth.

  • Holds moisture, does not import weeds
  • Its ability to hold on to moisture might make it especially useful in pots and raised beds, which tend to dry out faster than those at ground level, especially in hotter climates like ours. Since coir is sterile, it does not import weed seeds as peat sometimes does.

  • Good for seed-starting mixes
  • Its sterility and its ability to keep the soil open, allowing tiny roots space to grow, make it a good candidate for use in seed-starting mixes. In the pot, coir can make up to 40% of the mix in homemade mixes, and it can be added to proprietary soil mixtures, even if they contain peat.

  • Renewable resource
  • Most of the potting soils available in the nurseries and garden centers in our area have peat as a component. In fact, it’s sometimes not easy to find a potting soil that doesn’t contain peat.

    But peat is often considered to be a non-renewable resource because it takes about 25 years to build 1 inch of peat. Unopened peatlands have come to be recognized as important carbon sinks that help fight climate change by limiting the amount of carbon dioxide in the atmosphere.

    Coir is a readily renewable resource, and it provides similar benefits in soil.

    There are many reasons you might want to give coir a try.

    The Gardeners’ Dirt is written by members of the Victoria County Master Gardener Association, an educational outreach of Texas A&M AgriLife Extension – Victoria County. Mail your questions in care of the Advocate, P.O. Box 1518, Victoria, TX 77901; or vcmga@vicad.com, or comment on this column at VictoriaAdvocate.com.

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