WSU Extension

Garden Tips


written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

Gardeners may be wondering about the numerous new products containing coconut coir being touted as"better than peat." Being a huge fan of peat moss for use in potting mixes and for use as a soil amendment in our local soils, it’s hard for me to give up this "tried and true" organic matter and replace it with something else. However, there’s two reasons why gardeners like me should try to make this transition.

One reason not to use peat moss is that it has become quite expensive. I would suppose this is a result of higher gas prices and the distance from where it’s harvested in Canadian bogs to where it’s sold in the U.S. The higher cost of peat moss has made peat-based potting mixes prohibitively expensive for many gardeners.

The other reason for gardeners to turn away from using peat moss are environmental concerns about the harvesting of peat from bogs. Sphagnum peat moss, the superior type of peat moss for gardening, results from the slow decomposition of sphagnum moss and the build up over time of the decomposition products in the bogs. Bogs in Canada, Finland, Ireland, and Russia have been developing over thousands of years. Dr. Linda Chalker-Scott, WSU Extension Horticulturist says, "Peat moss is a non-renewable resource whose replacement takes centuries." Chalker-Scott has expressed concern because peat lands are "bio-diverse ecosystems with important functions in water quality and carbon storage."

Coconut coir is one material being suggested as a good replacement for peat moss. It’s a byproduct of the coconut processing industry. It’s made from the fibers found between the husk and shell of a mature ripe coconut. The brown fibers are high in lignin and are water-proof. "Coco" doormats and stuffing for automobile seats and mattresses are made from coconut coir fiber.

Researchers have found that coconut coir is a viable substitute for peat moss in potting mixes because:

1. It retains water as well or better than peat moss.

2. It drains as well or better than peat moss.

3. It doesn’t contain weed seeds or disease organisms.

4. Its pH is suitable for growing plants.

5. It breaks down more slowly than peat moss.

6. It’s easier to wet than peat moss, which is notorious for resisting wetting.

7. It’s a processing byproduct, making it a renewable resource.

This spring, I have discovered that some of our local garden centers and nurseries are carrying coconut coir. There are a number of different brands available in the area, most coming in compressed "bricks". You just add water to the dry, compressed ‘bricks" and their volume expands almost exponentially. Voile’

The fineness of the coir seems to vary quite a bit. Some that I bought is quite coarse with big chunks of coir. Another type has long fibers, but not the coarse chunks. These should work well for amending soil in flower beds, but are not as good as finer textured coir dust for use in potting mixes. I’m hoping that the finer coir dust materials will soon be readily available too... at a lower cost than peat moss.

Another byproduct that may soon become a suitable substitute for peat moss in the horticulture and gardening industry is a different type of fiber. It’s a byproduct of dairy manure. A WSU research team is looking at the feasability of using anerobic digestion to change manure into three useful byproducts. One byproduct is methane for energy generation. A second byproduct is struvite . This is a crystallized solid that’s rich in plant nutrients, such as nitrogen and phosphorous. The third byproduct is a high quality fiber for use in potting mixes.

Research by WSU scientists has shown that the fiber is a viable alternative to peat moss in potting mixes for growing greenhouse plants. Researchers have concluded that after a "post-digestion" treatment the fiber byproduct is "equal to or superior to peat moss when used as a major component of greenhouse potting soil." This manure bio-solid fiber is not yet available to home gardeners, but hopefully it will be before long. Just think... a manure byproduct can help us be more environmentally responsible gardeners. Wow!

It looks like these two peat moss substitutes will help wean me off of peat moss as soon as they become readily available and included in potting mixes on the garden store shelves. I’ll try to make the change, how about you?

May 19, 2007

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