The amount of organic matter may be too high which means that growing medium hold too much water. A soil that is too wet will have germination problems and plants will not be able to uptake and utilize nutrients well. A soil too wet can also cause numerous fungal diseases in plants, damping off is one well known result.

I added pretty much nothing but compost to my garden for 20 years and came up with very high K and P. If you're importing any organic matter in the form of compost, it's all going to have nutrients in it, not just manure compost.
A minor point though and not what you were asking.

It just sounds a lot like my garden. I have great numbers and poor growth.

I'm thinking along the lines of fungus too. Do you rotate crops? Do you fallow any of the garden and grow a cover crop? These might be good things to try.

I'd cut way back on the fertilizers and go easy on the compost because everything seems pretty high. I'm not sure why they're recommending to add K if it's already in the high range.

Raised beds usually provide very good drainage, just by nature of their elevation. But the lack of any mineral based soil, too uniform a particle size and the water retention of all that organic matter has offset any fast drainage characteristics. Personally, I think Mel's mix sucks - I just can't see that combo of ingredients providing a very successful growing medium for anything after the first season. Of course it's going to be excessively moisture retentive - peat and compost?? And any drainage assistance vermiculite might provide initially dissipates rapidly once the material becomes fully saturated.

The very coarse sand/gravel sounds OK but I'd skip the medium sand. Or you might want to consider adding something like perlite or pumice for a permanent drainage factor.

Thanks for the responses y'all!

toxcrusadr: I do try to rotate a I can given the limited space, but some things (e.g., tomatoes) can only shift across a few squares in each bed given how the beds are arranged. Given the poor germination this year, I suppose parts of each bed are effectively fallow, but never a whole bed and I have not grown any covers or green manures.

gardengal48: Why do you recommend against the sand? I was thinking that some grain size variation would be helpful as I try to build up a true mineral fraction. I head read that perlite will swim to the surface over time, which is why I was not thinking of using it. I don't know that I have seen pumice around the Twin Cities...What grain size were you thinking? My sense is that the first year with the Mel's Mix was the best and it has declined steadily since then, but certainly many folks on the SFG forum swear by it!

What about mixing in pine bark fines if I can find them? I have seen some threads discussing their benefits and it seems like they could help lighten the soil, increase aeration and aeration, and, at least according to some, won't particularly tie up N. Plus they might help decrease the pH a bit.

David

The problem is drainage. When the soil texture reads muck, your options are limited.

There is no such thing as too high organic content. If there were, no greenhouse in the country could produce a petunia, forget foliage, amaryllis, pointsettias, etc. but the media they use is carefully blended to provide drainage...not muck.

Pine bark would probably be a good addition...a large (relatively), coarse material blended in would probably do wonders to help with that drainage.

I do seasonal containers and in my mix I use lava rock, crushed to fit through a 1/2 inch screen as opposed to perlite. You lose some of the absorption capacity, but the density of the lava rock keeps it from floating to the surface.

As far as the nutrients...when the recs for fertilizer.come back at one tenth pound per hundred square feet...you need do nothing.

Lava rock is essentially pumice and yes, there is less tendancy with this to float to the surface. Pine bark fines are a great idea as well. Sand, whether medium grade or coarse, is just too fine a particulate to help much with drainage - you need large particulates for textural impact and durability, like what pumice/perlite or the bark would provide.

If you want mineral content, just add some plain ole garden dirt :-)

Hey gardengal48,

I actually do have a bag of "top soil" that I figured I would add also, but I need to check it and see what it looks like first. Thanks for your input!

David

I was thinking some silt, sandy silt, etc. would be a good way to get the mineral fraction up. I've never dealt with Mel's Mix though so I'm out of my element.