Coconuts for Your Roses

Patsy Cunningham


Like most gardeners, I like looking around nursery centers to see what new gardening tools and products they’ve come up with.  While wandering around a hydroponics store named Worm’s Way near Worcester a couple of years ago, I ran into a number of planting mediums I had never seen.  One of them was called coir, and it came in hard dry little bricks and in a much larger compressed block.  The packing described it as “expanding coconut fiber medium”.  It was midwinter, when it can be hard to find good seed starting mixes at most nurseries, so on the recommendation of the staff I gave it a try.


I started with a small brick, added the recommended amount of water, and was pleasantly surprised with the soft fluffy medium it produced after soaking.  I used it to start some rose seeds.  The first difference I noted when comparing it to some seed starting mixes was how easy it was to water.  There was no crusting at the surface and even if it was left to be almost completely dry, it was easily re-wetted with no surface pooling or run-off.  So, when it was time to start all my daylily seeds that winter, I went back and bought a big block of the coir.  The large block produces 2.5 cubic feet of medium, almost equivalent to a full bale of Pro-Mix or the like.  I figured on mixing up about half the block at a time, but couldn’t cut the darn thing up to do that, so I made a full batch. (Bob Forand also bought the large block and was able to cut it in half with a chain saw).  I mixed it in an inexpensive covered plastic clothes storage tub (you need at least the 18 gallon size for this).  This gave me plenty of seed starting medium and potting “soil” for the whole winter.


After all the seedlings were up and growing, I found the coir had some other advantages.  For the first time, I had no fungus gnats buzzing around the seedlings and eating the seedling roots.  There was no damping off at all, nor was there any fungus or algae growth on the soil surfaces.  I was sold on using this coir for seed starting and have used it since.  Another great feature it has, is that as sold it is almost completely dry, fully compressed, and “sterile”. It’s stored on nice clean store shelves, versus being outside in large wet dirty nursery yards where bagged mediums can become infested with insects or pathogens.  Because it is dry, it is not frozen into an unusable soil popsicle when you need it in the midwinter, even if stored in an outside shed.  Until it’s reconstituted, it’s easy to transport and store because of its small size and light weight.


So, I thought I’d look more into coir (pronounced “core”) and see what else I should know about its properties, uses and production.  Coir is often compared to a similar appearing product, peat moss.  Both are considered to be a renewable resource.  Sphagnum peat is deposited over hundreds and of years in bogs.  It accumulates only about 2mm per year on the bog and could become depleted with poor management.  Canada, our main source of peat moss, harvests about 10million cubic meters per year, but is actually accumulating peat about 70 times faster than it is producing it.  Coconut coir is produced from the pith of coconut shells.  In India and Sri Lanka alone, 10 billion coconuts are harvested yearly. It’s used there for stuffing mattresses, auto seats, ropes, erosion prevention and more.  They still have loads of extra coir for export.  It too is “renewable.”  The shells are shredded, sorted into long fibers and pith, and then aged and rinsed by the rains for a season in large concrete yards.  There are differences between the two mediums.  Peat has an acid pH, about 3.5-4.5, while coir is 5.7-6.7, closer to the needs of roses.  Peat comes from the ground, and can have weed seeds and pathogens while coir is produced “above ground” and has no opportunity to acquire soil contaminants.  Peat decomposes rapidly in use, with its particles becoming smaller and more closely packed over time.  This reduces the pore sizes in the soil, and the availability of air. It also contains more tiny particles than coir, which can cause waterlogging.  Coir on the other hand has more than 45% woody lignin in its composition.  This greatly increases the time it takes to break down, so it keeps the soil structure open and stable so air can penetrate.  This would be particularly useful for those who grow roses in containers.  The high lignin content also encourages the growth of soil microorganisms around the roots.  Coir easily rewets, even without a surfactant added.  We all know how impossible it is to wet dry peat moss.  As an aside, make sure that you soak and “fluff” your blocks of coir well in advance of use.  If it is not completely rehydrated before being filled into pots, the expansion of the coir will make it too dense.  When starting seeds, coir deters fungus gnats by keeping the top surface of the containers dry; they are attracted to a moist soil surface.  Peat based products are known to attract these pests.  In this way the coir acts like a mulch on the soil surface, while distributing moisture evenly with its natural wicking action.


Studies have found that the percentage of seed germination is increased in coir, and was particularly helpful with the difficult seeds of woody plants. Germination also occurred more quickly in coir, compared to other mediums.  Other studies have found that soil-less mixes with coir as an additive vs peat, produce plants with heavier growth of stems and roots.  It is thought that there is an antifungal property also that prevents pythium from causing damping off.  There are also significant amounts of phosphorus and potassium in coir.


All in all, coconut coir is great for seeds and container growing.  It would also be great for putting in the planting holes for roses as a moisture retainer that also keeps the air pores of the soil open for better root growth.  If you’re planting more than a few roses outdoors, this would quickly get too expensive with the coir products I’ve seen.   I understand it can be gotten in a bulk package that reconstitutes to 10 cubic feet, at a price closer to its peat counterpart. 

 (reprinted from the May 05 Rhode Island Rose Review)


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Date last edited: 01/21/10
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