Thursday, May 13, 2010

Using Coir to Start Seedlings: A Cautionary Tale

In previous years, I've successfully started large numbers of seedlings in peat based potting mix. This year, in an attempt to move away from peat, I switched to a coir/perlite mix.

For reasons that aren't entirely clear, things aren't working as I'd hoped. One of the reasons for this post is to let readers who were counting on me to start their peppers and tomatoes know that the plants aren't in the best shape. For all I know, the plants will recover when transplanted into a peat based potting mix. That's my hope. If you don't want to take that chance, you might want buy your tomato and pepper seedlings elsewhere.

First, the good news. The eggplants look incredible. Even better than what in previous years I'd started in peat based potting mix.

About half of the tomatoes and all of the peppers look unhealthy. It would be easy enough to say that the coir is to blame, as it's the major difference between this and previous years; but with all the glowing reports on the benefits of growing in coir, it could just be that I bought a bad batch. Or that someone put peanut butter in my chocolate. (Huh?)

I've sent out a sample of the coir to a testing lab, but the results won't be back for a while. The peppers look anemic, though with a recent addition of gypsum (to make up for the nutritional deficiencies of coir), there is some promising new growth. The tomatoes have some funny looking lesions and aren't as "bushy" as they've been in previous years.

If you're looking for another place to pick up a few seedlings, a couple places that sell interesting varieties come to mind.

Green City Market Farmer's Market (every Wed and Saturday)

Kilbourn Park Organic Greenhouse Sale (May 15,16, and 19)

I've been hardening off my seedlings, and for those of you who haven't been discouraged by my post, they'll be ready for pick up starting this Saturday, May 15th.

I'll add some pictures tomorrow when I get my hands on a camera.


Anonymous said...

Mmmm... I used coir pellets from Lowe's to start a bunch of my seedlings and they came up and did as well as I expected. I added nothing to them. I suppose it's always possible they were pre-amended with something. I hope you find your answers because I really would like to find a viable substitute for peat.

Greenscaper said...

Hi Bruce...IMO you should have an EC meter (for soluble salts testing) for what you are doing. I was going to buy one more than 5 years ago and didn't get around to it. I'll email you an info doc about EC meters. I do not have a brand recommendation. Google away!

Good luck,

Bruce said...

Hi Bob,

Thanks for the idea. And the link to How to use an EC tester.

At roughly $65, even the cheapest tester is a little out of my range. The coir sample I sent for testing will also be tested for soluble salts (for an extra $3). I'm hoping that will answer some of my questions.

oldgrowth said...

About the coir vs. peat: I've almost ALWAYS mixed my own potting mix - from the mid-'70s to present and my mixes have evolved over the years. My recent concoction has been approximately 60% peat-based mix (well-known brand), 30% coir, 10% perlite. This has worked WONDERFULLY for all my sips...and I don't feel coir content should be more than 50% as I am potting from 10oz Solo cups to 5 gallon sips. My latest recipe will include worm castings and vermiculite, not sure yet of the proportions but BOTTOM LINE...over all these years from "ghetto" drain/fill potting to sips...there is no substitute for peat in the mix. I feel less than 50% might be detrimental.

H2 said...

Hi oldgrowth:
I'm using about the same proportions in my SIPs that aren't in the experimental coir-pearlite mixture.

The latter seems to have real problems.

Using coir to extend the peat works for me. Also, I'm upping the pearlite too, for the same reason and to lighten the mix.

Thanks for writing!