Quality of bought-in compost and Seed Starting

I have a local supplier of compost that takes in food waste from the city and turns it into some nice black looking compost for a very reasonable price ($30 for a cubic yard).  I've been using it to form my market garden beds (sometimes right over the old beat-up pasture grass), tarping it for a period of time, and am seeing an explosion of earthworm activity when I go to broad fork a few months down the road. Seems like a good sign.

Recently I've been trying to use the compost to start seeds and grow microgreens when mixed about half and half with a peat/pearlite standard grow mix and have been having poor results.  Germination of winterbor kale and salanova lettuce has been spotty, the lettuce has a funky leaf curl, and microgreen flats start growing webby fungus along the top within a few days.  Curious about the quality of the compost, I put it under the 400x microscope -Elaine Ingham style- and found pretty much just straight bacteria.  No signs of fungus, nematodes, protozoa, or microarthropods.

I was wondering your all's thoughts on this bought-in compost. While it may not have a full compliment of the soil food web, I feel like it is a useful source of organic matter, just may need time for the organisms to develop once in the garden.  But as far as starting seeds/growing microgreens goes, do you think it could be contributing to the poor germination/fungus growth?  Any other thoughts on why my transplants aren't germinating? Setup uses a combo of t5 and LED strip lights.  Doing bottom watering, and I did mix a handful of organic fertilizer in with the transplant medium.  Currently running a trial with microgreens with straight potting mix to see if that helps with the fungus problem.  Any comments welcome, not the most experienced grower, but working on it!

Hi Karel, welcome to Permies.

It is possible that this compost is just very rich, and using straight compost even though mixed with peat/perlite is just too much for the seedlings. Seeds have all the nutrition they need contained within to germinate and sprout. High quality composts can be quite potent, and a little can go a long way, and it's certainly possible that this company is making some high quality stuff. It's also possible that there's still a some amount of nitrogen leftover from their composting process which may be fine for established plants but is too much for the germinating seeds. Perhaps try starting your seeds in just the peat/perlite grow mix and once they're up, apply a very light sprinkling of compost over the surface and water. Hope this helps!

I agree and it is probably not dully composted anyway which is not good for seedlings (I forgot why)

As we all know a lot of seeds are planted by animals. A lot of seeds germinate and grow quite well. However we don't know what the germination rate really is. That contradicts the idea that the seeds are equipped to support themselves. I'd say seeds planted by animals are more likely to germinate than seeds cast into the wind in the same field. I might be wrong I admit. I did plant mustard by hand sowing and they did quite well, uncovered. But I've also sowed a lot grass seed and covered them with mushroom manure.

My guess is that there's another issue effecting these seeds. Too hot, too humid....... Maybe a place for some ideas from the many out there with lots of experience.

Karel Bunker wrote:I have a local supplier of compost that takes in food waste from the city and turns it into some nice black looking compost for a very reasonable price ($30 for a cubic yard).  I've been using it to form my market garden beds (sometimes right over the old beat-up pasture grass), tarping it for a period of time, and am seeing an explosion of earthworm activity when I go to broad fork a few months down the road. Seems like a good sign.

Recently I've been trying to use the compost to start seeds and grow microgreens when mixed about half and half with a peat/pearlite standard grow mix and have been having poor results.  Germination of winterbor kale and salanova lettuce has been spotty, the lettuce has a funky leaf curl, and microgreen flats start growing webby fungus along the top within a few days.  Curious about the quality of the compost, I put it under the 400x microscope -Elaine Ingham style- and found pretty much just straight bacteria.  No signs of fungus, nematodes, protozoa, or microarthropods.

I was wondering your all's thoughts on this bought-in compost. While it may not have a full compliment of the soil food web, I feel like it is a useful source of organic matter, just may need time for the organisms to develop once in the garden.  But as far as starting seeds/growing microgreens goes, do you think it could be contributing to the poor germination/fungus growth?  Any other thoughts on why my transplants aren't germinating? Setup uses a combo of t5 and LED strip lights.  Doing bottom watering, and I did mix a handful of organic fertilizer in with the transplant medium.  Currently running a trial with microgreens with straight potting mix to see if that helps with the fungus problem.  Any comments welcome, not the most experienced grower, but working on it!

Compost is not necessary for sprouting plant seeds and for most it can be very detrimental, a seed is a lot like a chicken egg, the hatching chick has enough yolk sac left at hatching (sprouting) to survive for three or four days with out any food. A seed has this same "yolk sac" and it too can survive for around three days with no outside source of food.
Most professional growers I know use a nutrient poor starting mix, usually mostly sand or vermiculite with the tiniest amount of nutrient supplier organic matter.
The reason for this is that once the seed sprouts, excess nutrients means a growth spurt at the exact wrong time, that means the seedling shoots up so tall that it can not support its own weight and so it falls over.
Excess nutrients at sprouting can also cause deformities to appear in otherwise healthy sprouts.
That webby fungus is most likely a type of mold not a fungi.

I would recommend you cut the amount of compost back by 7/8ths of what you used in the current mix, everything you have mentioned about the seedlings points to far too much nutrient available at the wrong time.
Adding an organic fertilizer to the high nutrient potting mix only compounds the problems.

I have started many flats of seeds in just sand, nothing else other than water, it works far better and the plants get a good start and don't end up spindly shafts that fall over when the cotyledons open up.

Redhawk

Thanks for the input y'all!  What you're putting down makes sense so I will be tuning the mix way down for the next trays and will report back.

This conversation has opened up all sorts of questions related to seeds and compost...  Should I not amend my beds too heavily with compost immediately before seeding?  I've also starting an air-prune bed to start tree seedlings this year that has a heavy amount of compost with potting mix that has been stewing with a thick leaf mulch over the winter.  Now I'm thinking of digging out a lot of it and turning the compost content way down as well.

Thanks again!