I gardened in SF clay for decades so I know what you're talking about. You cannot work California clay in January. That is the rainiest month, and right now you've gotten huge amounts of rain even for January. Wet clay should not and cannot be worked. I never planted anything in the ground (pots only) in December or January - the clay is too wet and too cold. A planter box should have purchased soil mix in it. Not clay. The comment about using plastic is to protect soil about to be planted in from getting excessively wet. Not for the whole yard. I would instruct my clients to tarp the area they wanted me to plant fruit trees in so it would be workable. Once clay is wet, you have to wait for it to drain a few days before you can work it. (Hence the tarping beforehand.) Squeeze a bit in your hand. If it squeezes through your fingers and remains in one piece with ribbons sticking out where it came through your fingers, it's too wet. It should crumble at least a little bit before you try to work it. When it's dry enough, compost is the best thing. Gypsum does not work in California clay. You will not transform it overnight, or even in a year or two. It will always be clay, and that's not a bad thing - I miss clay. Here I'm gardening in dirty gravel, with no water retention or nutrient retention or any measurable organic matter. Most trees and shrubs will grow in clay just fine, with annual additions of a little compost. Lettuce and other vegies are a different story, they need a looser soil. That's where mounding up amended soil comes in. Dig up the clay, add some compost and maybe some purchased topsoil, and mix it all together and heap it up above grade. Don't just lay stuff on top of the clay and then plant in it, as water will sit on top of the clay and the plants' roots will then be sitting in water. Mix it up so it grades from amended soil to the native clay. Compost helps any soil, clay or sand. You just can't work clay soil after all that rain you've gotten. You'll have to wait for it to dry a bit.

In case the link is ever broken, cut and paste the PDF file here: Linda Chalker-Scott, Ph.D., Extension Horticulturist and Associate Professor, Puyallup Research and Extension Center, Washington State University The Myth of Gypsum Magic âAdding gypsum to your yard or garden will improve soil tilth and plant healthâ The Myth Upon continued prodding from one of my university extension colleagues, I recently watched several episodes of a well-known gardening program on television. My kids joined me, alerted by my animated responses to the hostâs non-stop torrent of advice. Among many amazing discoveries I learned that by adding gypsum to my yard or garden I would improve my problem soils by changing the particle size and loosening compaction. Further searching on the web revealed that gypsum would also improve drainage, decrease acidity, and eliminate soil salts. Previously, I had heard of gypsum for use in soil reclamation projects, but not for a typical urban landscape. Since gypsum is simply calcium sulfate, could this chemical truly transform soil structure and serve as a fertilizer for yards and gardens? The Reality This myth falls into the category of agricultural practices misapplied to ornamental landscapes. Gypsum effectively changes the structure and fertility of heavy clay soils, especially those that are heavily weathered or subject to intensive crop production. Gypsum also improves sodic (saline) soils by removing sodium from the soil and replacing it with calcium. Therefore, one can see improvement in clay soil structure and fertility, and desalinization of sodium-rich soils, by using gypsum. What other effects will gypsum have on soil and plant health? There are a number of scientific studies on gypsum usage both in the literature and on websites. Briefly, researchers have found: ⢠Gypsum does not usually change soil acidity, though occasional reports of both increasing and decreasing pH exist; ⢠Gypsum can increase leaching of aluminum, which can detoxify soils but also contaminates nearby watersheds; ⢠Gypsum can increase leaching of iron and manganese, leading to deficiencies of these nutrients; ⢠Gypsum applied to acid soils can induce magnesium deficiency in plants on site; ⢠Gypsum applied to sandy soils can depress phosphorus, copper and zinc transport; ⢠Gypsum can have negative effects on mycorrhizal inoculation of roots, which may account for several reports of negative effects of gypsum on tree seedling establishment and survival; ⢠Gypsum is variable in its effects on mature trees; ⢠Gypsum will not improve fertility of acid or sandy soils; ⢠Gypsum will not improve water holding capacity of sandy soils; and ⢠Gypsumâs effects are short-lived (often a matter of months) With the exception of arid and coastal regions (where soil salts are high) and the southeastern United States (where heavy clay soils are common), gypsum amendment is just not necessary in non-agricultural areas. Urban soils are generally amalgamations of subsoils, native and non-native topsoils, and - in home landscapes - high levels of organic and non-organic chemical additives. They are also heavily compacted and layered (and gypsum does not work well on layered soils). In such landscapes, it is pointless to add yet more chemicals in the form of gypsum unless you need to increase soil calcium levels. This nutrient deficiency can be quickly identified by any soil testing laboratory for less than a bag of gypsum costs. (If you need to improve sulfur nutrition, itâs wiser to use ammonium sulfate). To reduce compaction and improve aeration in nearly any landscape, application of an organic mulch is more economically and environmentally sustainable. The Bottom Line ⢠Gypsum can improve heavy clay soil structure and remove sodium from saline soils ⢠Gypsum has no effect on soil fertility, structure, or pH of any other soil type ⢠Most urban soils are not improved by additional gypsum ⢠Before adding gypsum or any chemical to a landscape, have soil analysis performed to identify mineral deficiencies, toxicities, and soil character ⢠Adding gypsum to sandy or non-sodic soils is a waste of money, natural resources, and can have negative impacts on plant, soil, and ecosystem health For more information, please visit Dr. Chalker-Scottâs web page at http://www.theinformedgardener.com.

My first garden was created 5 years ago...we took off the sod, amended with compost, tilled and planted and mulched. It was a nightmare. I probably needed 60 times more compost, and never could have afforded it. The following two years I hated working in the garden because it was such hard work with the clay and many plants didn't thrive. I replanted areas many times and each time I would add more compost/mulch, whatever I could get my hands on. I also added a soil conditioner that was very expensive but works like gypsum...breaks down clay. (Who knows, maybe it WAS gypsum with a bigger price tag.) It's 6 years later now and I have to tell you that the garden is just a delight to work in now. I plan to spread gypsum a couple of times each year and continue mulching the beds, but I'm sure I'll never have to do all that double-digging like I did before....just keep on piling on the stuff like everyone wrote above, and before you know it, your beds will be as you need them to be. I also highly recommend that you search out plants that LIKE clay, so that your plantings will be successful. I spent many, many dollars buying plants that needed more drainage than I had and would die...and I wondered why. Some of those plants might do ok for me now in the same garden, but I think it's important to plant things that actually LIKE the ground that they are in today. Good Luck!

When did you transplant your peonies the first time? Is the amended soil in a raised bed? The only issue I could think of is a possibility of poor drainage with a clay base so close, otherwise you should be fine. Have the peonies been in place long enough to tell if the area is going to get boggy? I can tell you from experience they don't like wet roots, they'll rot! Most people do divide the larger roots, they take quite an effort to dig out once they get bigger, don't they? Better to do it once and done with moving and dividing them! That said, as long as there were enough feeder roots kept intact to support the number of eyes on your larger peony it'll probably be okay. A lot depends on how the rootball looked when you dug it up. If the middle was really woody with little or no eyes with all of the healthy looking parts on the outside of the root, I'd dig it back up and divide it to encourage new eye/root formation. Some of them get that way and will just start dying out from the middle. If the whole thing was a mass of fleshy, tuberous roots with healthy eyes then you're fine. I would think 3/4" of soil over the eyes is just about perfect for your zone.