I have never heard that vermiculite turns to concrete, but as my sft beds are only a year old, I can't speak with experience.

I did a search on the forum and didn't turn up anything that would confirm, either.

Here is a link that might be useful: my garden page.

fernwood; I would go to your library and check out Mel Bartholomew's book New Square Foot Gardening. He explains the mix quite well. Then explains about how much compost to add and when.

Curt:)

Nothing organic lasts forever, but I've never heard of it turning into cement. Mel recommends adding new organic matter every time you remove one crop and plant a new one, so, theoretically, it shouldn't have a chance to turn to cement. The extension agent may have been referring to the peat, which can get as hard as cement if it dries out too much, though.
And too much nitrogen will indeed cause big leafy wonderful-looking plants, but not much fruit. Could be the mushroom compost, so maybe you should add a bit less of it and more peat or use some other kind of compost in combo with the mushroom compost.

The person there said they don't recommend vermiculite because as it gets old it gets like cement.

If you call that office again, you may want to talk to a different agent for advice.

Dan

Also remember that Mel specifies a compost BLEND, meaning using several different sources of compost because one source may not have enough nutrients. So I would add other sources of compost to your mix.

I've never heard of vermiculite getting hard. I know it breaks down with age which is why Mel recommends that you start with coarse.

Cassie

My beds are not old enough for me to say from personal experience, but I have never read any complaint of vermiculite hardening over time. I have seen some people report a bad experience with peat with regard to hardening. Because of that and/or because peat can be considered unsustainable, some recommend coconut coir as an alternative to the peat.

I agree that you should add other types of compost to diversify the available nutrients.

Resurrecting this thread just in case someone in the future has a similar question: it's not the vermiculite that hardened, it's the peat moss. There are several reasons this could have happened, including proportions that were slightly off in the first place; mixing that was less than thorough; walking on or otherwise compressing the bedding mix; and, last but not least, that's just something peat moss does sometimes!

I second Dan's advice to talk to a different extension agent next time you call though. Sheesh!