Thursday, May 6, 2010

Testing and Amending Coir

I'm not giving up on coir yet......Our neighbor, Carol, has been growing greens successfully in 2 bucket SIPs using coir. That suggests to me that coir will wick water in the same way that peat does. One difference was that she bought her coir from a local source, Brew and Grow. The coir they sell is roughly double the cost of the stuff we bought from Rolanka.

I like beurmann's idea of sending out a sample to be tested for nutrient levels and excess salts. He left links to several local testing companies and generously offered to split the cost. The first test is on me, if this gets expensive I'd be happy to take him (you?) up on it.

One the same subject, thanks, too, to our friends at Homegrown Evolution for pointing me to a great, cheap testing lab for any kind of garden soil -- UMass Soil Lab. I tried calling them to ask if testing for excessive salts in coir was possible and was asked to leave a message in a full voicemail box.

I'm a little confused by what kind of test I need to have done. Take a look at one company's menu of testing options. Does coir even count as "garden soil"? A phone call to one of testing companies might clear things up.


In any case, it looks like I'll need to amend my coir with garden gypsum and epsom salts to get a soilless mix that transfers nutrients to my plants. From "tapla" at the GardenWeb Container forum -
Sphagnum peat and coir have nearly identical water retention curves. They both retain about 90-95% of their volume in water at saturation and release it over approximately the same curve until they both lock water up so tightly it's unavailable for plant uptake at about 30-33% saturation. Coir actually has less loft than sphagnum peat, and therefore, less aeration. Because of this propensity, coir should be used in mixes at lower %s than peat. Because of the tendency to compact, in the greenhouse industry coir is primarily used in containers in sub-irrigation (bottom-watering) situations. Many sources produce coir that is very high in soluble salts, so this can also be an issue.
Using coir as the primary component of soils virtually eliminates the reasonable use of lime or dolomitic lime as a Ca source because of coir's high pH (6+). Gypsum should be used as a Ca source, which will also help eliminate problems associated with coir's low S content. All coir products are very high in K, very low in Ca, and have a potentially high Mn content, which can cause antagonistic deficiencies and interfere with the uptake of Fe.
He, "tapla", gives some specific directions on how to amend the coir later in the same thread -
OK - I like peat much better, but of course it's your soil. ;o) Add 1 level tbsp of gypsum per gallon of soil or a skinny 1/2 cup per cu ft. Because you should use gypsum as a Ca source in coir-based soils, you'll need to use MgSO4 (Epsom salts) as a source of Mg, and so the Ca:Mg ratio isn't so skewed that you create a Ca-induced (antagonistic) Mg deficiency. Use 1/8-1/4 tsp per gallon of fertilizer solution every time you fertilize, or every other week if you're attempting to insure nutrients via organic soil amendments.

More information that suggests that adding gypsum is the way to go -
Coconut coir, a by-product of the coconut industry, has been promoted as an alternative to peat moss in soil-less media. Sphagnum peat moss has long been a standard component of soil-less media, but some people have expressed concern that it is a non-renewable resource. Although it does not appear that world peat resources will be in short supply for a very long time [nevermind the habitat loss and release of sequestered carbon, ed.] , coconut coir may have characteristics that make it a useful component of soil-less media mixes. Coir has been considered to promote excellent plant growth but there are few rigorous studies that have compared it with peat moss control plants. However, ten years ago, Meerow (1994) found that growth of Ixora coccine was significantly reduced compared to growth in a sphagnum peat moss control. Vavrina (1996) found that there were no adverse effects of coir to tomato and pepper transplants, but a subsequent study in the same lab (Arenas et al., 2002) found that media with more than 50% coir had reduced growth compared to peat-grown control plants. They suggested that a high N immobilization by microorganisms and a high C:N ratio in the coir may have caused the reduced growth. Lopez-Galarza (2002) found that root development of strawberry plants grown in peat moss was better than in coir in some, but not all, studies. Handreck and Black (2002), in a comprehensive textbook on soil-less media, review the chemical and physical properties of coir dust that are being sold in Australia. They indicate that since all coir products have extremely high K contents and low Calcium contents, it is critical to add a source of Ca to improve plant calcium uptake. Since the pH is already close to 6, liming materials cannot be used because they would increase the pH above optimum. Handreck and Black says that “Therefore, all coir-based media must be amended with gypsum, which also overcomes their low sulfur status.” [emph. added] Ma and Nichols (2004) recently reported that the problems with coir extend beyond its high salinity. Their data indicate that high concentrations of phenolic compounds in fresh coir are at least partly responsible for the growth reductions observed in other studies. Several studies at the USU Crop Physiology Laboratory indicated that monocots grown in coconut coir were extremely chlorotic and stunted. The objective of this study was to see if there are differences among plant species and types of coconut coir compared to growth in sphagnum peat moss.


Anonymous said...

Thanks for this info. I have read Taplas erudite posts before. He sure knows his stuff. I will be heading to the store to get me some Epson salts.

Bruce said...

Another helpful study on the properties of coir - (pdf file)

"Coir dust has better capillary wetting properties (capillarity) than peat and most other common potting mix ingredients."

"A good quality coir dust should not be any more saline than peat (EC
<0.5 dS/m)"

buermann said...

The concern with the coir and salts is specifically a high concentration of sodium from sea water. You'd want to ask the lab if they can get a good reading on that to find out if Rolanka's coir was sufficiently weathered or if we picked a lemon. They might have left the husks to weather on the beach for two years, etc.

I've been amending my mix with garden gypsum (way too much, by the sounds of it, in the last batch), as I'd read that also. The epsoma tomato tone fert I'm using has Mg, but it sounds like I should be mixing that in a bit and lighten up on the ring.

After that last post though I decided I'd add in peat so *something* would grow either way - about 40:40:20 peat/coir/perlite.

Oh, and that cucubrit mildew - a baking soda solution is supposed to protect the plant from infection if you spray early:

If we keep track of the spread of outbreaks at we should be able to hose down the cumbers in time, without too much hassle. I started weathering mine yesterday and they didn't care much for the rotten weather :)

Anonymous said...

Coir is always far easier to re-wet than peat, which is a major advantage.

Rinse the coir before using it down to EC 0.0 or 0.2...

mhals said...

I've been lurking for a year or two. Thanks for the inspiring blog - i started 2 years ago with 2 SIPs of heirloom tomatoes on my garage roof w/ great success.

I experimented with coir last year in 2 additional SIPs - coir from a pet supply store (reptile bedding). 40% coir, 40% peat, 20% perlite; organic vegetable fertilizer into the top 6". Greenbeans, lettuce, carrots, and onions all stunted.

I'm really curious about results from your soil test. I've left my coir mix out in the rain this winter in hopes it will wash out salt. I'll add gypsum and epsom next year and see how it goes.

in regards to plastic hats vs mulch - my tomatoes with a fertlizer strip and a plastic hat performed *much* better than mixed fertilizer and mulch - a moisture retention issue?

thanks again - enjoy your winter!

Bruce said...

Hi mhals,

Thanks for sharing your results. Very interesting.

It sounds like the coir is problematic, all the more reason to figure out what's going on before writing it off. I never heard back from UMass about the sample I sent in. To tell you the truth, I'd forgotten that I even sent it. Time to send them another one and see what they say.

My 80% coir, 20% perlite SIPs performed terribly. It seems that 40% coir might be too high as well. Maybe 20%? I'll try that percentage this coming year.

The plastic v. wood mulch is another problem area. With an eye toward reducing plastic use, I want the mulch to work. Others (the Montreal Rooftop Growers come to mind) have successfully replaced the plastic and used wood chips. I've made the switch and haven't noticed much of a difference, but both you and H2 have got better results with the plastic covers.

buermann said...

I had really good results this summer with the 40/40/20 rolanka coir/peat/pearlite mix, though it turns out I didn't add enough gypsum after all and had a lot of early blossom end rot - a couple spoonfuls straight into the reservoir took care of that.

Bruce said...

Hi Josh,

Thanks for the info. I, too, had ok results with the 40/40/20.

Unknown said...

Coco coir is an environmentally-responsible growing medium that provide benefits over other components used in weed farming. However, weed gardeners should understand that coir and/or sub-standard coir plant foods may result in problems with blood potassium, metal, mineral magnesium, calcium, mineral, and phosphorus components that might impact the growth. I’m patiently waiting to analyze the new pH Ideal coir products, and will keep you updated. Waiting to have more fun with coco coir…and less work using it!

Unknown said...

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