First you need to look closely at that soil to determine what it needs and that requires a good reliable soil test for soil pH and major nutrient levels and balance. Things like cottonseed meal need to be digested before the nutrients in them are available to plants and if the soil has little organic matter the SFW is not there to do that. Whether cottonseed meal, or any other meal, would help would depend on the Soil Food Web and how active they were. Whatever your 'landscaper' used for 'topsoil' was probably about 95 percent mineral (the sand, silt, clay part of soil) and 5 percent organic matter and what your soil really needed was organic matter. Know the characteristics of the site, understand limitations, and select your plants accordingly. There are some things we can do to alter, change, and improve the situation but oftentimes those fixes are temporary, at best. One of the first steps of good landscape planning is to select plants that will do well in the given site. Lavender requires excellent drainage, period. Water will pool in the planting hole because it cannot escape quickly through the clay. 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. We have to add a heavy mulch of OM every year. We then amended our planting beds with lots and lots of organic material from various sources. The front yard used to drain slowly, but we fixed that with some sub-surface drainage tile. I have very heavy clay soils, but they are not wet. That is, unless you are willing to maintain it on a regular basis. (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. It won't do the trick, either, but it won't raise the pH. She may have been thinking of gypsum (sulfur + calcium), which is often touted as a 'clay buster'. That's something you don't want to do unless a professional soil test indicates that you need to. There's nothing in dolomite (magnesium + calcium) that will do anything to improve clay soils, but it can sure increase your pH. I'd disagree with her on the addition of dolomite, however. DaisyDW is right: organic matter is the ultimate amendment for clay soils. Sand is useful only when you actually replace most of the clay with sand. You'll end up with something more akin to cement.
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