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What to do about failed seedlings planted in coir?

Maynard, MA

Each year, I start many seeds indoors with grow lights and heat maps (this is New England, after all). I never have much trouble. But this year, although all of my seeds germinated, they haven't been growing. Hardly any of them have true leaves, although I planted them over a month ago.

I'm pretty sure the problem is that I used a different growing medium this year; in fact, that's all I did differently. I used coir, which is a growing medium made from shredded coconut husks. Does anyone know a remedy/nutrients to add to coir that might help my seedlings grow??? It's too late to start new ones.


Phoenix, AZ(Zone 9b)

If it were me, I would find a good, robust seed starting mix and repot. There are many to choose from and hydroponic stores have a better selection, imho, than the big box stores. Nurseries would be second best if you don't have hydro stores. My all time favorite is Roots Organics, it's in a camoflauge patterned bag, also like Happy Frog or Light Warrier from Fox Farm. Again, these are found easily at hydro stores, not sure nurseries would carry, upscale probably do.

Hope this helps somewhat.

Charlotte, NC(Zone 7b)

ShaynaPearl - did you add fertilizer to your potting mix?

I use a mixture of coir, worm castings, perlite and vermiculite with added amendments and have absolutely no problem with seedlings sprouting and growing into strong transplants.

Saylorsburg, PA(Zone 6a)

I love coir as a growing medium but also add worm castings. When the seedlings have a second leaf I then feed with a diluted fish emulsion. The seedlings are generally doing great. The only one I am having a problem with is Swiss Chard. I've lost a lot of the seedlings to wilting. I think the coir was too wet and they don't like that. But tomatoes, peppers, eggplants and flowers are growing beautifully. Sometimes I also think I may be adding too much worm castings. Perhaps adding some perlite or vermiculite like you do Honeybee would help.

Charlotte, NC(Zone 7b)

Here's my potting recipe:

1 brick classic coir soaked in 4qts hot water makes a little over one gallon
1 gallon worm castings, keep bag closed after each use to prevent drying
2 gallons coarse perlite
1 gallon vermiculite


2 tablespoons bone meal with iron
teaspoon trace elements
4 tablespoons dolomite lime
cup soil moist
cup Numus
1 cup crab shell
1 tablespoon phosphate

Phoenix, AZ(Zone 9b)

honeybee, do you use this mix for germination or after germinated you pot up with this? THanks.

Charlotte, NC(Zone 7b)

Mary - I use this potting mix from the day the seeds are sown, until they are set in the garden.

I add a dusting of vermiculite across the top of each cup after seeds have been sown. The cups are 3oz plastic Solo cups.

I also add water to the potting mix plus this soluble fertilizer on day one.

I know some/most wait until the seedlings are up before they add fertilizer, but I have never done so.

Another thing I do... I leave a shallow film of water in my trays at all times. The seedlings drink as needed. I don't water from the top, only from the bottom. I punch holes around the bottom edge of my planting cups and another row about 1/4 inch up from the bottom edge. I keep the water level just below this 1/4 inch level. I rarely have seedlings die of damping off.

Saylorsburg, PA(Zone 6a)

Thanks for your formula, Honeybee. That is a lot of worm castings !!! And I thought I was adding too much worm castings to my cups! I always add more worm castings when I transfer to the straw bales or garden soil. I will definitely add some perlite and vermiculite next time. Since I grow organically I will substitute for a different granular fertilizer over the Miracle-Grow and stick with the fish emulsion as well. Very helpful!

Everett, WA(Zone 8a)

Some batches of coir arte said to be a litle salty, anf that stunts seedlings, especially as any added fertilizer builds up.

Here's a question: is your coir coarse enoguh and fastg-draining enough that you can aford to flood them with fresh water, from the top, and expect it to drain out the bottom without drowning the roots?

If yes, then maybe flush them a few times with warm water to try to cary away as many ions as possible. Then, fertilizing them won't make matters worse.

However, if the problem is just that the coir IS too fine to allow fast drainage and adequate aeartion, nothing is likely to help other than potting up and knocking off the sodden coir that roots have not penetrated. If you pop a few plants out of their cells to check, and the roots have not taken over most of the mix, probably there was not enoguh aeration.

That's one theory, anyway. You might pot up 6 seedlings, and flush 6 others, and see which benefit more.

One trick to partly mitigate the damage from poorly-draining mix in small cells is to sit the cells firmly on something absorbant, like a towel or four-layers of Tee shirt or cotton flannel. This may pull enough water out of soggy cells to let the roots breath and use more of the volume of the cells. You can leave the fabric or other kind of capillary mat in the tray,. just pull out excess water with a turkey baster until the plants are in pots tall enoguh, or fast-draining enoguh, to give them some air.

Roots are like people in that not-enough-air will kill them faster than not-enough-water.

Charlotte, NC(Zone 7b)

gardadore - I prefer to use organic fertilizers, too, but when I use them indoors, I have problems with damping-off.

I do use organic fertilizers once the seedlings are set out in the garden.

As to my soil recipe, I think the abundant amount of perlite offsets the worm castings. I've tried equal amounts of each, and had seedling failure. One part coir, one part worm castings, one part vermiculite and two parts perlite seems to do the trick.

Saylorsburg, PA(Zone 6a)

Interesting about organic fertilizers and damping off! Were you using fish emulsion or a granular fertilizer for the organic? Since worm castings are quite expensive I was wondering if it would work to halve or quarter the amount of them and reduce the perlite as well? I usually only add a tablespoon of the castings to my cups which are 9 - 16 oz. The bag says that a small amount of the castings goes a long way! I don't use the worm castings with the coir until I transfer the seedlings to the larger cups. It is to those cups that I plan to add the vermiculite and the perlite next year.
Will have to rethink things for next year!

This message was edited May 12, 2012 8:57 PM

Charlotte, NC(Zone 7b)

gardadore - I used fish emulsion.

It takes several seasons to empty one bag of worm castings, and it goes into the garden along with seedlings, so it doesn't go to waste. I've tried all kinds of homemade potting mixes, and this one works for me.

Maynard, MA

I wish I had asked you-all about coir before purchasing it. (I also wish the company I bought it from had mentioned that it should not be used alone as a growing medium. After I posted my question here, I called the company and spoke with their head gardener, who said she always mixes her coir with compost and would never use it alone. Too bad she didn't tell her customers that!)

As it is now, I realize that even if I could revive my seedlings, most would be way too small to put in the ground by the time we're safe from frost here--I wouldn't have enough growing time left to harvest them.

Ouch. Lesson learned the hard way.


Cleveland,GA/Atlanta, GA(Zone 7b)

Re: Rick's point re: coconut fiber/coir based products for planting is a good one. This product is mostly harvested overseas and on tropical beaches. It is generally high in salts since the product virtually lays out on the beaches while being processed. I have seen it in production and can say, "buyer beware". When I'm not growing veggies I am growing species orchids. Orchid growers that use coconut fiber chunks as a medium know it should be soaked in several changes of fresh water, over several days, to be reliably free of salts. I use coconut fiber products in the greenhouse with my orchids. Species orchids have exacting requirements. Some distributors of coconut/coir products may advertise an already desalinated product and others may not. I have rarely seen instructions that include soaking the product. I soak everything in at least two changes of rain water, regardless. I am also a vegetable gardener. There are numerous budget friendly starter mix alternatives to coir.

Saylorsburg, PA(Zone 6a)

I go through a 30 lb bag of worm castings each year as I add at least a cup to each planting hole for the tomatoes, eggplants and peppers when I transplant them into the straw and hay bales. In the earth boxes I add at least another cup or two. I was wondering if adding a diluted mix of hydrogen peroxide and water to the coir cups would help with the damping off and then allow me to use the fish fertilizer. Somewhere I read on DG that hydrogen peroxide prevents damping off. Just a thought. Does that sound reasonable?

Phoenix, AZ(Zone 9b)

I use a weak solution of cammomille tea in the bottom watering reservoir. I've never had a problem with damping off since I started using the cam tea. I will also add H2O2 if I remember.

Cherry Grove, OH(Zone 6b)

Coir is a substrate. On it's own, it has little or no nutrient value. All of the advice above, about adding nutrients, would help tremendously.

This message was edited May 25, 2012 7:00 PM

Liberty Hill, TX(Zone 8a)

Thats what I always considered it. It just occupies space for you to sow seeds or put plants. all the nutrition is up to you., which an be good because you can customize it to fill the plant's particular needs.

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