Define rock garden.

Uncertain why this was posted on "buying and selling houses" but you might want to delete then post again only in landscaping. Before you do people will need to know what kind of rocks you are using. Some people simply place rocks then fill the areas between with soil or if a dry rock garden fine scree/small rocks. Type depends more on your weather than what your soil is. Plant Select on FB has many pictures of what would be called rock gardens but it is working with what they have. There is another company that has dug down and placed flat rocks vertical then filled in between. If you want to keep these suggestions copy and paste before deleting this posting.

If you are planning on doing a rock garden to sell a house in one word Don't. It is not something most people want.

To start, 'clay soil' and 'rock garden' is an oxymoron. Plants common to rock gardens tend to demand very good drainage, something rarely present with a clay soil. There are ways to get around this but you will need to do a lot of work to get a properly plantable area. And I'd suggest that adding a bunch of rock and whatever you want or will grow under existing conditions is not technically a 'rock garden' but just a garden with a bunch of rocks scattered around! There is a big difference!!

With the cross posting feature this site pushes, it really doesn't make much difference where one posts as long as you hit at least one forum where it is applicable. btw, there are several GardenWeb forums that are appropriate in addition to Landscape Design, including Alpines and Rock Gardens and Gardening with Stone.

Buy suitable well draining soil from a dealer, dump on top of clay and plant in that without mixing any of it with the clay.

The new soil layer will of course have to be deep enough - as in berm or mound - to provide adequate conditions for the new planting.

This is my recent experiment for a rock garden on top of clay: A gently sloped berm made with a base of large quarry rock (as big as my husband could safely lift), with the spaces between filled with medium rock, small rock, sand, pumice, and loam. Planted with mostly sempervivum and then topped with a layer of small gravel. Watered only with soft flow (to prevent erosion) when water is necessary at all. I recommend doing it in a location with full sun or afternoon shade and no overhead deciduous leaves. A lot of work to install and would be a lot of work to remove if the next person didn't like it. Good luck!