I tried gypsum for a couple of years per pkg. directions in my hard adobe. I saw no improvement. Later read gypsum works only with certain types of clay soil. Over my head technical wise. I vaguely remember the author naming some midwest states where it would be effective.

If I pry a chunk of my unimproved and whack it, nothing happens. Doesn't crack in two, doesn't dent, nothing. It can be sliced if semi-moist. Even bindweed fails to thrive. It's more like rock than soil.

So if your soil is like mine, lotta work ahead. The bearded iris roots need to go down at least 12 inches. Mine stayed spindly and didn't bloom until I got rid of about 4 inches and dug in organics. Now the bindweed thrives.

How often do you water newly planted rhizomes in the summer? It's around 85'F this week. I read this from the schreinersgardens website. Only water once every couple weeks? I doubt it's enough?

• In very dry areas, water newly planted Iris once very well at planting time, then again every couple weeks. A gentle tug on the top of the foliage is a good test to see if the new roots have set in.

• Established Iris beds need very little to no water during the summer. The exception would be "reblooming" Iris, which require more water to encourage rebloom.

Gypsum is mainly a way to add calcium and sulfur to soils that are more alkaline. It would be hard for me to say if the addition of it was what helped my gardens, since I did other amendments to the slightly clay soil I had at my other house as well. I add it here sometimes since my soil now is freely draining in most of the yard and nutrients just leach away when it rains a lot. But there is already a lot of lime in the soils here, and in some places naturally occurring gypsum. I would think that organic matter would be more important to add, and breaking through the hard pan, or building a heap on top of it. B
indweed knows what are the good places to be, that's for sure!

I had clay soil at my last house on the SF Peninsula when I was a lot younger and more determined.. I dug out a bed 3' down, then sifted it back in the hole alternating gypsum, oak leaf compost, & fir mulch. I mixed it all in and planted. After a few years, it was back to what it was before I amended it, minus the rocks. I think it did get the tree off to a good start, but I've learned not to fight the soil. Raised beds are a good way to go if you have really heavy clay.

Ouch! Trying to alter the soil for a tree is not "best practice". Sometimes the tree will never put roots outside the zone you amended, which stunts it eventually. "Fighting" is not fun, and the less of it one does the better one likes gardening. You can learn over time which varieties like your area and do well in the soil and climate you have.

Lessons learned in life.. That was some 25-30 years ago. The tree actually did well.. The area I dug out was 6'x 8'x 3-4'. A lot of soil had been moved around haphazardly when the house was built, plus a lot of building debris just thrown back in. The soil below that wasn't as bad, and I transitioned it well, so it wasn't night and day. But I agree with you to a degree. If you just dig a hole and amend it in clay soil it just becomes a receptacle to hold water. I've learned that you can only fight the soil and environment to a point. If something doesn't work in my soil, there are other things that do.

Amen to that! I'm glad the tree did well. After all that work I'd have given up on gardening if it hadn't. My shoulders are sore just thinking about it!

Gypsum will only work on clay soils that have a high sodium content. When gypsum is added, the Ca++ ions in the gypsum (Calcium sulfate) allow the sodium (Na+) ions to be leached out.

This allows the negatively-charged plate-like clay particles to escape out of their densely-packed alignment, breaking up the matrix. The clay negatively-charged particles then cluster around the positively-charged calcium ions, which opens up channels through which air and water can travel.

If the clay soil you have does not have a high sodium content, then addition of gypsum does not work in breaking down the clay.