I'd go with Al's 5-1-1 mix, but with some modifications.

I'd use uncomposted bark as the base, I'd increase the amount of perlite, and I'd probably
choose a more durable ingredient like Turface to take the place of the peat.

This is just a shoot-from-the-hip brainstorming. Al would be the best man to help tailor your mix.


Josh

Two questions:

Why do you WANT to water twice per day?

Why does the mix get changed twice each year?

Al

Hey Al,
Thanks for checking in. In response...
1) I am looking to water more to allow the media to not always be saturated and also for the nutrients to not build up and become toxic. I would like to be able to keep the nutrient levels consistent and allow the plants to dry up a bit. I am growing tomatoes and heard flavor is better when this occurs.
2) I am planning on two tomato plant rotations in the greenhouse...could do one, but refreshing the tom plants might be a good idea and would allow me to rotate varieties and work the seasons more efficiently.

All input is truly appreciated, Al. Thank you.

If that's what you really want, you'll probably need to go with a rather coarse bark with the fines screened out (use everything under 1/8" for something else, mixed with coarse perlite, Haydite, or pumice in about 1/8-1/4" size.

There was a thread about a source of calcined DE around, that mentioned a store that sols a product that was quite a bit larger than Turface and more uniform - that might be worth looking into. If anyone has it saved, would they share, please. I'll see what I can find in a search.

Al

See the link below for a discussion about the relative sizes & amount usable product between different DE products.

Al

Here is a link that might be useful: Click me, click me! I'll show you!