I first put in a drainage of coarse sand and stones between the GH and the highbed.
![Image](http://www.cactiguide.com/forum/userpix/2513_Hochbeet_2011_Maerz27_002_1.jpg)
Then I layed 3 layers of old brick around.
![Image](http://www.cactiguide.com/forum/userpix/2513_Hochbeet_2011_Maerz27_003_1.jpg)
![Image](http://www.cactiguide.com/forum/userpix/2513_Hochbeet_2011_Maerz27_005_1.jpg)
Next will be some more stones for drainage, then a layer of water permeable fleece to prevent the substrate from filling the holes of the drainage layer. And then the substrate for the outdoor cacti + some more bigger stones.