The very best way to amend soil (either sandy or clay) is to dig in plenty of organic matter - which means compost. For clay soils, toss in a few handfuls of dolomite - otherwise known as 'clay-breaker'. I could never be bothered by mixing loam and sand and other stuff in. Compost does a brilliant job.

I never worry too much about the soil for my herb-only garden. It had plenty of compost dug into it when I first moved here, and since then, I've just kept up the mulch (I use sugar-cane mulch because it's cheap around here), which rots down over time and needs topping up a couple of times a year. The soil is now beautifully friable.

Lavender prefers a well-drained soil, pH 6.5-7.5. You can improve the drainage by planting on the top of a mound (hill) made by heaping up some of the amended soil.

Lavender prefers a fairly poor soil, so go very easy on the fertiliser if it's in the garden. A potted plant will always be hungrier and thirstier than one in the garden. I find that a handful or two of compost spread as a mulch around potted plants once or twice a year is quite enough.

Why not start your plant in a pot, using any good quality potting mix, even a special 'herb mix'. Meantime, start digging your garden.

Thanks so much..Perfect advice.

It has me on track now.. I was blind about the whole thing. I was thinking digging dirt up, then turning in some sand and compost then putting it back in the hole. But I didn't know if the roots would hit the clay and then die. I don't like the idea of mounds b/c it's my front yard garden...hoping I could do it in-ground but not too deep.

How wide and deep do you think an average lavender plant will get?

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.

I have heavy clay too and I agree as well, organic material is the way to go. If you don't already have them, build compost bins. They will become your friend!

And even though you have clay, situating your garden in a good spot is key. Don't locate it in the low areas which do drain slowly. Locate it in a place that has reasonable drainage - even for clay. The top of an area that slopes may be one such place. Water would naturally run away from there. Go learn the characteristics of your property for best placement and results.

Also agreed on not making "port-holes" of well draining soil in the clay. Water will pool there. Amend an entire garden bed for best results. And with many of the Mediterranean herbs (lavender, thyme, sage....) lean soil is desired so you don't have to go crazy with rich soil. You can mix some regular top soil in with the organic material/compost for the herb bed.

FataMorgana

Thanks so much! You guys are great... This is my second year trying to grow lavender..last year I killed both of my lavenders and 1 I threw out b/c I thought it was dead, but it was just giving a dead dried up look due to the pruning. I read this was normal.

I have 20 seedlings right now growing. 'Munstead' and 'English'.

I was thinking about building an entire new bed for the lavender. Digging up the clay soil bed completely..maybe a foot 1/2 deep....and adding new soil...

Also, thanks so much for reminding me about clay and sand...I read about that a few days ago..and it left my mind. Maybe I would have remembered in the process of doing it..but probably think it was ok. I think I will save my sand for my lemon plants.

In the new bed...I definitely want to put some of that gypsum on the floor of the bed and then some small gravel. Then lots of compost mixed with the dug out clay soil, and I think I will also add some store bought garden soil into the mix too.

Then maybe fill the holes and then create small mounds and then plant the lavender.

I don't know how deep lavender roots go...

Maybe I could plant some wet loving plants between the lavender...to soak up all of the water that may pool. I don't know...I'm going to have to think about this one...or dig the garden bed deeper.

The addition of gypsum will do nothing to help the problem with the clay soil (it's 95% myth, save your money), and adding a layer of gravel at the bottom of the bed may end up causing problems before too long. Your best bet is to remove some of the clay, but then DEEP till the amendments in with the clay at the bottom, so that you have something of a homogenized mix to plant in.

More problems are caused by the artificial layering of different medium layers than you could ever realize. This is especially true when improved materials are layered on top of clay. You will still get the bathtub effect. By mixing it all up, you'll have a mixture that will drain deeply.

The addition of gravel at the bottom, rather than improving water drainage, will simply raise (lessen) the level of the rooting depth. The fines from your new soil will eventually filter down to the gravel like silt, creating yet another barrier against the infiltration of water. This is true whether we are using the gravel in the ground or in a container.

So, the simpler, the better! Mix your clay with lots of good, coarse OM (compost, bark soil improvers, etc.) and you'll probably end up with something pretty superior. That is, unless the site is just plain soggy regardless of what you add to the soil.

I think I am just going to build a raised bed and put new soil in it. Better than dealing with the clay soil.

I think that you need about 10 to 12 inches of good soil with drainage, not several feet deep. The herbs roots shouldn't be that deep. Secondly, the water, by gravity, will sink down even in clay, although slowly. But if you get heavy rain day after day after day, No soil can drain all that water right away, unless it is mostly sand.
Here is the most clear agvantage of a raised bed, about 10" higher than walkways around it. Not that the excess water will be drained faster, also no run off water from ellsewhere can get into it. And that is why most herbs gardens, on a level property, are raised.

We have clay soil...all clay soil....and mom uses gypsum all the time, with good results.

I have six horses, so I put in a LOT of aged horse manure. I try to put in almost as much manure as I have soil. I only plant Hidcote lavender, which seems to be okay with getting more water (next to the roses) and doesn't mind the richer soil.

Since Hidcote lavender is an english lavender, maybe that's why it does well in these conditions. For a french or spanish lavender, I would put them in pots or raised beds, with other mediterranean herbs.

I'm still pretty new to all this, so I hope this helps. Biggest thing I'd recommend is try something and see if it works (especially if it's not expensive) you can always put raised beds in later, if you need them. Sometimes you learn more from (hopefully inexpensive) mistakes than any other way :)

I have almost pure clay soil and my lavender plant is huge and almost continuously in flower. However I planted it on the uphill side of a retaining wall that I backfilled with gravel and then covered with clay, so I suppose it does get good drainage. I also have four huge Rosemary plants that have turned into a hedge they are so big and thick, and again are almost always in flower. The bees work my yard 360 days a year.

Does cow manure compost that can be purchased at home & garden centers work well for the compost?