Growing in the Bath!

This old bath was a water trough used by the cows grazing in the field when we bought it (and indeed afterwards, although nobody thought to mention it. The owner of the cows is well known for sticking his animals on any empty bit of land. Complain to the mayor they said. Guess who is acting mayor?!)

   
After ten years of various uses, it is now going to be a planter for all the herbs that love our heat but hate our clay

The bottom half is full of boulders dug out of the borders and veg beds and we've topped it off with a trailer load of broken roof tiles. They were free, rescued from a heap where they had been thrown off my neighbour's roof which is being replaced. I'll be topping it off with some weed matting and then a mix of broken down (I hope) turf, shop compost and a bag of gravel.

   

The planned plants are a pair of prostrate rosemary plants at each end (I've taken cuttings from an ancient and now very pot bound one in a beautiful curved pot that I can't get it out from), lavender and then a load of different thymes, some to creep over the edges ...

Anything else I should be considering?