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FYI: straight compost has limited utility as growing medium (soil free raised beds)

 
dan long
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Experience is the best teacher. Learn from mine; not your own.

I made a raised bed (my vvery first) with nothing but compost on top of newspaper. Starts do outstandingly in this medium but seeds have very poor germination rates. I didn't even realize that this counted as 'poor germination" until I dug up one section to bury some fish and then sowed into the exposed, native soil and found myself thinning far more than before. I did some searching online and found other people saying that compost is too light and doesn't retain water (what i originally suspected to be the cause) well enough for small seeds to germinate.

Prior to this, I planned on making some huge, foot high beds upon returning to Washington with composted horse stall bedding. I now see that this setup would be impractical for plants that must be direct seeded (root vegtables and cilantro). But i could spread some native clay on top and sow into that if neccessary.

That isn't to say that you cant grow in straight compost. My starts faired excellently. The squash i threw in the compost pile is sending out volunteers: in the beds, in the pile itself, and in the field where compost fell out of the basket accidentlly. This suggests to me that large seeds can do ok (i presume because they can be buried deeper where there will be more water). I had pretty good germination with both red and white radishes but that seems to be the lower limit on the size of seeds you can direct sow. My onion and lettuce seeds have fared dismally. Corn and beans germinated about the same in compost as they did in soil. Pumpkins appear to have similar rates as well. Coriander did so poorly that the ONE plant I got (out of a few dozen seeds) came up months after sowing, in the wrong season and promtly bolted in the heat. Carrots had similar performance, though I got some tiny roots.

Compost is many things and provides many benefits, but don't think it is a suitable medium in itself! It is satisfactory for starts and large seeds but small or difficult to germinate seeds will disapoint you. Get some topsoil on the surface if you want to direct sow those small sees.
 
William James
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Location: Northern Italy
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I recently planted carrots on compost and they seem fine. The compost had lambs quarters inside it, so I'll be harvesting that too.

I would say you probably need to water the compost every couple days to keep the surface moist, like you do with potting soil when starting plants. Once they get started I think they'll have enough root to get water for themselves.

In another case, I planted a mix of cover crops, no water, I could see the seeds for 10 days baking in the heat and not germinating. I'm hoping with this recent rain they'll finally get started. They needed a week or so of bad weather to get started on compost.

I read somewhere that expecting plants to do well in straight compost is a no-no, as plants want to grow in soil. But I thought I'd experiment with some crops like carrots that just can't grow here because of the heavy clay soil. I wanted to give them some contact with soil at the ends of their roots, so maybe putting compost in a raised bed would work - maybe with a wood or brick border. They would have soft soil to get be in, but they'd have the benefit of getting their roots into real soil.

William

 
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