Compost generally isn't actually very "rich" in the first place, unless you've mixed in fertilizers. Some sources, perhaps like composted poultry manure might be a little "richer," but most are pretty low-key in fertility.

Especially since you are establishing a garden where sod used to be, I would err on the side of adding the compost, as you normally do. I just wouldn't add fertilizers. I was surprised that one of my books, "Gardening with Perennials" claims that lavender takes average to rich soil, but I wouldn't test that!

I've got a healthy five or six-year stand of lavender in my English Cottage garden in the back yard in full sun. It is quite a trouble-free and lovely plant. I have decent-draining clayey loam in that spot. I tried to dig so I could get you a picture, but the ground is frozen now. I always add compost when I plant something.

By the way, the deep purple of lavender makes a lovely combination planted in front of pale yellow moonbeam coreopsis! This photo was primarily of the coreopsis--the lion's share of the lavender was in the foreground, off-camera.

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in the case of lavender, drainage is going to be more important than other factors, ie, organic content or fertility. Plants that truly desire waste lands of infertile soil are rare; most are quite adaptable as to fertility, soil type, etc where wet feet are only barely tolerated. They may be adaptable/tolerant to poor, infertile soils, that does not mean they must be grown in them.

If you are working with compacted clay, one thing to be considered is subsoil drainage. Drain tile may be used, or you may dig a couple of deep holes and fill with course material to the bottom of the planting bed. Once, in a courtyard planting, we had to do this under every tree we planted. Of course, we only learned this after replanting them three times...

Oh good to know. I will keep the compost in then! Ha, I am terrible about remembering to fertilize so leaving out that at will be no trouble at all. That is strange that book said rich soil! Some of mine say poor sandy soil so I have been second guessing myself. Thank you for sharing your experience, and for the suggestion of moonbeam coreopsis as well! I was actually thinking of pale yellow as an accent but hadn't come up with a flower yet. I will check that out!

Hi Strobiculate, I have heard of drain tile but I'm not sure I'm picturing the right thing. In another area of the yard, below a gutter, I dug a trench 3' out and ~1.5' feet deep and installed a perforated plastic pipe to pull water out and away from the house and the roots of a shrub. Does that sound like the same concept as the drain tiles or deep holes? How deep did you dig the holes? Our front yard does have a very slight slope away from the house and to the right, which should help but I don't want to take any chances.

Many herbs, such as Lavander, we are told prefer to grow in "poor" soils which are not very well defined for us. What you need to know is something about the mediteranian soils Lavender evolved from, generally rocky limestone, well drained (or maybe closer to arid), with not much organic matter.

When dealers are trying to sell a plant they push the maximum boundaries. Lavenders will do well in sandy soil without much organic matter. I don't think they will do well in clay, but it can't hurt to try out new concepts. Clay would have poor drainage so some OM would increase drainage. You want great drainage for lavenders. Rosemary is aggressive in my area. Lavenders are a bit more fussy. The thing about gardening is you never know until you try out a plant how it will do. There are so many factors to consider such as climate. I would start out with just one plant, before planting many plants.

drain tile, many different actual substances, same end result. I have fields that still have clay pipes in sections about 2-3 long and 6-8" diameter that either work their way up through frost upheaval or get pulled up by the tillage equipment.

But what you described works too.

As to depth of the holes, that's a trick question. If your soil has a strata that impedes water draining, all you need to do is get through it. Otherwise, essentially you are creating a well to store the excess water (runoff, er, drain through). Benefits and drawbacks. Do what you can, and if you have to...Perovskia?

Strobiculate, okay, I'm clear now. Thanks for getting back to me.

Here's my current plan based on everyone's replies. I'm going to amend the entire area down at least 12 inches, getting rid of much of the current clay soil. Yesterday I found a soil amendment called "Sweet Earth" from a good local garden center, designed specifically to increase the alkalinity of the soil for perennials and annuals. I'm going to mix the Sweet Earth and a gravel-like soil perfector (i.e. Permatil) with the remaining clay. I'm thinking an end ratio of 30% clay, 50% Sweet Earth, 20% soil perfector. For some of the lavender plants, I'll dig holes as deeply as I can and fill the bottoms with coarse gravel. It'll be an experiment to see if they fare better/same as/worse than ones in soil that's only been amended. I'll be growing the lavender from seed so I'll have cheap replacements for casualties.

If anyone thinks I need to amend deeper than 12" or shoot for a different ratio of components, let me know. I'll post back with results and if I had to go with the Plan B Perovskia. :)