1) add the gypsum when you make the soil. It is added as a Ca source, I've been trying some plants w/o gypsum this year because I use Foliage-Pro fertilizer, which contains both Ca and Mg. It appears that everything is fine w/o it, but it's been too cold for plants to grow robustly, so I'll have to let you know in a few weeks if you need to add gypsum when using Foliage-Pro. You definitely should add it when using soluble fertilizers that do not contain Ca, so you need to read the label for contents.

2) If you use gypsum as a Ca source when you make the soil, you should add Epsom salts each time you fertilize. The reason is because a high presence of Ca in the soil in relation to the amount of Mg can make Mg unavailable. The Ca:Mg ratio should be around 3 to 5:1, Ca:Mg.

3) I'm not an orchid grower, though I do have several hardy terrestrial orchids that are doing very well in the gritty mix and are multiplying well. I don't hang out on the orchid forum either, so I don't have a feel for whether or not it suits some orchids. As I said, I'm pretty ignorant about orchids, but it makes sense that all the terrestrials would like it, even if you had to modify it slightly by going up a size in grit or decreasing the amount of Turface to reduce water retention. That would be a good question for the Orchid Forum.

Can you elaborate a little on your last question so I have a better chance at collecting my bonus? ;o)

Al

Al, Thanks for the answers, I understand it better.

Bonus question was this - I am in southern cal, probably on a filled subdivision. The soil is very heavy, gets hydrophobic easily. Probably clay+silt?
My question was how to amend this to grow healthier plants?

Lots and lots of organic matter. If you can till some in initially, go for it; if not, lay sheets (lasagna) of organic matter where you intend to plant and wait for the soil fauna to till it in for you.

There is an issue though. Unless you can drain water away, you'll eventually develop a bathtub effect. The soil under the organic matter will become more friable and have more air space. This means it will hold more water in the 'tub' until it can percolate through the soil or unless you can drain it away. Hopefully you're on at least a minor grade?

Al

Perhaps I can help with the orchid part of the question... hi, Al! I was in the neighborhood... :-)

Anyway... I've got a few different orchids... Phals, Dens, Epis, etc... all growing quite happily in a rendition of Al's gritty mix. Just keep an eye on the watering. No problems.

I don't know what the ground is like in Southern Cali, but here in the Midwest, it's clay with a sometimes shallow hardpan... or it can be rocky with intermittent areas of dark soil... difficult to dig and grow in.

As backbreaking as it is, I'm sold on preparing beds the old fashioned way... hard work, lots of amending, sweat equity! I turn it over by hand, digging deeply... and before that, I remove any sod. I add peat, sand, composted manures and leaf debris... leftover potting soils... turn it all in... and I let the bed sit over winter.

The best thing any serious gardener can do is start a compost pile... within a relatively short amount of time, depending on how you care for your pile, you'll be pulling loads of black gold out from under it... and that's one of the best things to amend garden soil with!

Patience is another good gardening ingredient!

Good luck!

thanks al and jodi, will amend with patience :)
Thanks for the orchid tip.

JODIK!!!!!!!!

Sorry, I couldn't contain myself, proceed..:-)

Mike

If you use gypsum as a Ca source when you make the soil, you should add Epsom salts each time you fertilize. The reason is because a high presence of Ca in the soil in relation to the amount of Mg can make Mg unavailable. The Ca:Mg ratio should be around 3 to 5:1, Ca:Mg.

Al, how about if I'm already fertilizing with FP which contains some Mg? Should I still be using Epsom salts?

Can I take a stab at this Irv?

If you have already added gypsum into your mix, then you should to make Mg available by using the Epsom salts, since a high amount of Ca in your mix, which you will have, will make any Mg unavailable, even if it is in your Foliage pro..

So assuming you added nothing to your gritty mix, then Foliage Pro alone just might be enough. But I will see, and I think Al will once we have been using it long enough..

If you should decide to still use gypsum, the you should use the Epsom salts too along with the foliage Pro..

Please correct me Al, if I am mistaken..

Mike..:-)

Thanks Mike- I moved a few plants into Al's gritty mix slightly over a year ago and they are doing OK, but I did not know that. I must have been absent from class that day !

So what do you think, about a tsp. per gallon?

Hi Irv..

I do what my mentor taught me..Here is an excert from a previous post.So far so good, my plants are thriving..

Mike..:-)

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Posted by tapla z5b-6a MI (My Page) on Thu, Jun 12, 08 at 21:06

Don't worry about repeat questions, B.
Instead of lime, use gypsum (1 tbsp/gallon of soil). The pH of the gritty soil mix should come in at just under 6.0 before liming, which is almost perfect because media pH tends to rise as it ages. Lime supplies both Ca and Mg, but it raises media pH. Gypsum supplies Ca and S, without raising pH; that's why I use gypsum as a Ca source in the gritty mix and then supplement the Mg by adding 1/4 tsp Epsom salts to the fertilizer water every time I fertilize. This regimen has worked very well for me over the years when growing in the gritty mix.

If you were using the 5:1:1 bark:peat:perlite mix, I would stay with the dolomitic lime @ the same rate - 1 tbsp/gal soil.

YPA

Mike's right - so you have the answers you were looking for, Irv?

Al

I sure do. Thank you both very much!

pharaoh,

I have the same clay soil problem here in Northern CA.

Too much compost is detrimental. I experienced a reverse bathtub effect. I dug holes and put in 100% compost for planting tomatoes/squash,.. When watered the compost would drain and dry out, but the clay below would stay wet. So I'd have to water more to keep the 1-2feet of compost moist. The clay then stayed waterlogged. Not great for the plants. They came in at about 1/2 their normal size.

This year I dug out the compost and am going with just the native soil mixed with leaves. Double digging seems to loosen the soil up enough, at least for 1 season.

This fall, I'll plant many deep rooted cover crops; lupines, mustard, cereal oats. Next spring I'll just cut them, no digging and plant away.
Hopefully this will allow a no-dig garden with reasonable soil that has the same "friability" down 3 feet or more.
Here's a source about cover crops.
http://www.sarep.ucdavis.edu/cgi-bin/ccrop.EXE
I've been looking for ones that have flowers, deep roots, lots of root mass, and are easy to kill with one cutting.

Also someone here posted awhile back that they mixed turface in with soil when they were planting city trees next to pavement. They said it worked well.
I did mix some turface in a small soil bed plot to test this. It does work. Plants did great and the soil stayed friable, but didn't dry out like the 100% compost beds did. Doing this large scale though would have required tons of turface and a lot of work.

pharaoh,

I have the same clay soil problem here in Northern CA.

Too much compost is detrimental. I experienced a reverse bathtub effect. I dug holes and put in 100% compost for planting tomatoes/squash,.. When watered the compost would drain and dry out, but the clay below would stay wet. So I'd have to water more to keep the 1-2feet of compost moist. The clay then stayed waterlogged. Not great for the plants. They came in at about 1/2 their normal size.

This year I dug out the compost and am going with just the native soil mixed with leaves. Double digging seems to loosen the soil up enough, at least for 1 season.

This fall, I'll plant many deep rooted cover crops; lupines, mustard, cereal oats. Next spring I'll just cut them, no digging and plant away.
Hopefully this will allow a no-dig garden with reasonable soil that has the same "friability" down 3 feet or more.
Here's a source about cover crops.
http://www.sarep.ucdavis.edu/cgi-bin/ccrop.EXE
I've been looking for ones that have flowers, deep roots, lots of root mass, and are easy to kill with one cutting.

Also someone here posted awhile back that they mixed turface in with soil when they were planting city trees next to pavement. They said it worked well.
I did mix some turface in a small soil bed plot to test this. It does work. Plants did great and the soil stayed friable, but didn't dry out like the 100% compost beds did. Doing this large scale though would have required tons of turface and a lot of work.