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Gypsum for heavy Mid-Atlantic Z7 Clay?

Posted by glitterglass Z7 (My Page) on
Wed, Sep 10, 08 at 16:00

Hi there.

I can't even remember where I read it at this point, and my search of the iris forum here didn't turn anything up, but I did read somewhere that gypsum should be added to the soil to aid in drainage when planting Iris. I live in Washington DC and we have good old-fashioned clay.

I believe I came upon the gypsum suggestion when one Gardenweb member warned against the use of my normal soil amendment, Bumper Crop, since she found the East Coast variety to contain high amounts of Nitrogen.

After trying to balance various recommendations on the soil preparation and fertilization of Irises, I purchased one bag each of Espoma Gypsum (for drainage), Bone Meal, and Bulb Tone (the latter two for fertilizing). I was told that if using the Bulb Tone, which has a Nitrogen count of 4, I wouldn't need to use the bone meal.

Any thoughts are welcome.



Follow-Up Postings:

RE: Gypsum for heavy Mid-Atlantic Z7 Clay?

See link below. I too have clay and remembered reading about the use of gypsum.


Here is a link that might be useful: Gypsum Helps Recondition Clay And Hardpan Type Soils

RE: Gypsum for heavy Mid-Atlantic Z7 Clay?

I have California mountain red clay soil (the type where if it rains enough and you sink and when your husbands pulls you out your shoes are still in the mud and they are not good for anything but to be toss out) and the way I deal with it is to dig it out and put it somewhere else and order good fill dirt. I tried adding stuff and I would have to add so much it was better to dig it out. In some places I lay down cardboard then wire for gophers and put fill dirt right on top.

RE: Gypsum for heavy Mid-Atlantic Z7 Clay?

Thank you---that's the best-looking link I've seen on information regarding gypsum use.


What a story! Haha. Thanks for your response. That's more or less what I usually do with Bumper Crop, a soil amendment with compost in it. They recommend using 1/2 compost material (like Bumper Crop) and 1/2 regular soil for backfill, but I typically put in more compost than clay when filling the hole again.

However, I am planting Iris this time, so a member here alerted me to the fact that Bumper Crop could be damaging with its high Nitrogen content and I started looking for alternatives... gypsum was one of the ideas.


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