Monday, May 3, 2010

Round 2: Coir vs. Peat in a Sub-Irrigated Planter (SIP)

On April 12th, I planted four SIPs--shown at left in the pic above--with the same control group of greens--tatsoi, bok choy, chard, rapa--and fertilizer.

The variable was that each SIP had a different soilless mix. Three weeks later, the early results are in.

SIP #1 - 30% one yr old mix (coir/earthworm castings, peat) from my potato box experiment, 50% 3 yr old BAACTO (peat based) potting mix, 20% perlite.

SIP #2 - 70% Three year old BAACTO potting mix, 30% added perlite

SIP #3 - 40% Three year old BAACTO potting mix, 40% coir, 20% perlite.

SIP #4 - 70% coir, 30% perlite.

I bought the coir from Rolanka and reconstituted it with water. The wetted volume is what is referred to in the above formulas. According to the literature, it is a superior growing medium as well as an eco friendly substitute for peat. Which is why I want it to work.

After these initial tests, my sense is that, unfortunately, the coir doesn't perform as well as potting mix. A maximum of 40% coir seems to be a good bet. Of course this could change, it's still early.

We'll keep doing tests on other types of plants throughout our growing season.


Anonymous said...

I used coir for the first time this year as well and I too have noticed that the tomatoes growing in the coir buckets are not growing. I thought about the pH being a problem but I have not checked it. Also, I wonder if the coir requires more nutrients at the onset. Thanks for sharing your research!

H2 said...

I think it doesn't wick well. Seed-starting trays with coir are one thing, but wicking 18 inches up (in the case of the 5-gal SIPs) ain't happening.

The only time my coir/perlite plants look good is after a rain, when they actually...get watered.

buermann said...

I picked up the same brand of coir on Bruce's suggestion and tested the ph, which was fine at 6. I'm more concerned about salts, but poor wicking sounds plausible too.

Uli Westphal said...

Hi Bruce,
Too bad # 4 didn't work out with those greens, i had such high hopes for the coir/perlite mix.
Do you remember how much % coir was in #1 ? It looks quite okay.
I'm slowly starting to transplant my seedlings to self build SIPs, making up different mixtures as i go. I think that most of my plants are way overdue for transplanting (the tomatoes are up to 2 feet tall, in half liter pots), but it took me a while to get started, and to make up my mind about what to use as potting mix.
I have now several test plants with different coir/peat/perlite mixtures. But for all the plants that i would really like to thrive I intend to use this mixture: For 6 gallons: 40% coir, 40% peat, 20% perlite + 1 1/2 cups of dolomite lime + 1 cup of earthworm castings + 1/2 cup of 5+4+6(+2+3) organic, dry, granular, fast & slow release fertilizer mixed in.
Just if you have the time: Do you think that this mix would work or do you have any suggestions on how to make it better ? I don't want to use the surface-fertilizer-strip for now. Do you think the amount of mixed in fertilizer is enough ?

About the peat situation: I found out that here in Germany there is a law that requires companies to only harvest peat from bogs that have been dried out already for a long time, most of them before the 70ties, for agricultural use. Any intact swamps/peat bogs are under environmental protection. Many companies however are importing peat from the baltic regions, where such laws probably don't apply. So for now I will only buy peat that is harvested in Germany, and hopefully find a renewable substitute in the future...
I will let you know how the coir experiments turn out over here, as soon as I can see some effects...
Best, Uli

Bruce said...

Hi Josh,

Thanks for checking the ph. It's nice to know that it's not a problem. I wonder how you could check the salt level? The Rolanka site claims that their product is fine, but how would we know?

Hi Uli,

I'm going to say planter #1 has at most 15% coir in it. My potato box mix was roughly 40% coir, 40 % peat, 15% perlite, 5% earthworm castings. If I multiply the 40% by the 30% that I put into planter #1 three weeks ago, I get 12%.

H2 theory is that coir doesn't wick the same way peat does. (Whenever it rains the plants perk up.) I wonder how you could test that?

I would use the recommended amount (per the label on the bag) of fertilizer mixed into the potting mix. I'm not using a fertilizer strip this year, instead mixing it into the top 6" or so, like you would a regular container. If I need to add more fertilizer half way through the season I'll push aside the mulch (replacement for the plastic bag cover) and mix more in.

Why are you using so much lime? For tomatoes it helps prevent blossom end rot, but otherwise you don't need it. Or is it to lower the ph?

Thanks for offering to share the results of your tests. We'll look forward to hearing more.

buermann said...

Soil lab tests aren't, all in all, too expensive:

There's a number of labs around:

I'd be willing to go in on it with you. It's not going to tell you about the wicking, but pushing a finger in and feeling how wet it is ought to answer that.

Uli Westphal said...

Hi Bruce, thanks again for your advice ! I added the lime to adjust the ph-level. I did tests before and after with a cheap electric ph-meter, which i believe is not accurate at all, but can give you a general idea. Before the lime it tested 4.5 on average. I tested it again two days after adding the lime and the result was 6. Today i tested again, and the ph-level went up to 7. Probably it takes a while for the lime to act on the soil ? I'll will reduce the lime to 2/3 cup and also try a chemical ph-test on it, which i hope is more accurate.
The ph-meter that i have now can also measure the moisture of the soil (through conductivity). So i will use this function to test and compare how the different mixes wick over time.

knoxruss said...

Bruce -

Do you not use a plastic cover on your SIPs? Or just these?


Bruce said...

Hi KnoxRuss,

I'm breaking with the orthodox on the mulch cover this year--I won't be using one.

After reading closely the pdf from the Montreal Rooftop Growing Collective - -- I decided that I would mix the fertilizer in the potting mix and cover the mix with ordinary pine bark mulch. It works for them, I'm thinking it'll work for me.

A couple of reasons for this--I want to stop using so much plastic and it'll make the end of the season clean up easier.