Calcium bentonite tends not to be the best clay to use for sealing ponds for the simple reason that it doesn't expands sufficiently to give a good seal. I suspect that you'd find they are most likely using sodium bentonite, or in some cases, kaolinite. In the use of clay for sealing basement walls, for example, it is sodium bentonite which is typically pumped/applied in and around the footing and walls of the structure, again because of it's expansion properties. That being said...what is, I think, important is that folks can find an inexpensive source of calcium bentonite without paying the outrageous prices for something which is most likely packaged from the same source and then marked up ... a lot! Thanks Horton, for locating an inexpensive source for you folks up Nauth! At least they won't have to worry about Customs!! One other point...I'd suggest that you make sure you get a finer particle size if available. The reason I recommended something similar to the Panther Creek PC-200 in another post is that greater than 70% passes through a 200 mesh screen. Some of the bentonite sources are a bit coarser and may not provide the same surface area or the same ion-exchange properties. Just a thought/recommendation. ---David

Lux again, after considering everything, I think the failure of Marachal Niel' to thrive, might be the clone. Because in the same bed, and c. 7-8 feet on- center from M.N. is a 'Mrs. B.R. Cant' that was given to me as a house present in January 2013, it arrived in a gallon pot and was c. 8 inches tall by nearly as wide, now it has grown to be c. 3 feet tall by nearly as wide in less than 7 months. I had planned to keep it in that bed for a couple years until it grew to be about 3 feet tall until I had cleared a strip of lawn to move it to, but it's grown three times faster than I thought it would have done. I'm still moving Marachal Niel' to a rosebed that gets a couple hours of afternoon shade, because two canes are sunburnt at the top of the plant, The yellowing leaves may be due to using Epson salts,this year and last, a tip I read in an English rose book. I should have understood that a method and means used in England may not be a good thing to use in California, because our soil and climate is so different. Thanks again, Lux.

Never add sand to clay soils. You'll end up with something more akin to cement. Sand is useful only when you actually replace most of the clay with sand. DaisyDW is right: organic matter is the ultimate amendment for clay soils. I'd disagree with her on the addition of dolomite, however. There's nothing in dolomite (magnesium + calcium) that will do anything to improve clay soils, but it can sure increase your pH. That's something you don't want to do unless a professional soil test indicates that you need to. She may have been thinking of gypsum (sulfur + calcium), which is often touted as a 'clay buster'. It won't do the trick, either, but it won't raise the pH. (Sodic clay soils can be improved by gypsum, but you don't have that kind of chemistry in Knoxville.) It is very difficult to alter the soil conditions of a site. That is, unless you are willing to maintain it on a regular basis. I have very heavy clay soils, but they are not wet. The front yard used to drain slowly, but we fixed that with some sub-surface drainage tile. We then amended our planting beds with lots and lots of organic material from various sources. We have to add a heavy mulch of OM every year. I've come to love our clay! Your idea of amending for your lavender on a hole-by-hole basis won't work for very long. You will create a bathtub effect. Water will pool in the planting hole because it cannot escape quickly through the clay. Lavender requires excellent drainage, period. One of the first steps of good landscape planning is to select plants that will do well in the given site. There are some things we can do to alter, change, and improve the situation but oftentimes those fixes are temporary, at best. Know the characteristics of the site, understand limitations, and select your plants accordingly.

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!