Question concerning raised beds

[Joel143]

Hello everyone. I'm not new to cactus but am to raised beds which I am in the process of making. Have a question. My raise bed will be about 24" in depth. I've read I can't really amend my local soil and just place the raised bed on top due to I would be making a pool when it rains. My local soil is organic dirt which turns to more clay in the mix the deeper you go...maybe a foot or two depending. The mix I will be placing in the bed for the 24" above ground will be a fast draining mix naturally due to the rain in my area (southern Louisiana). My question or concern is the cactus will do great in the raised bed but what happens as the cactus grow and their roots continue growing into the local soil? With the local soil holding more moisture during the rain would it damage or rot the cactus? The bed will be in an area near my house that, to me, drains nicely but might stay evenly moist. A Cycad palm and some angel trumpet plants are in the area now which I will be moving.

Any info would be great because this makes me nervous. I would hate to lose the large cacti I plan to be placing in my raised bed. Cacti will include some cereus (Pachanoi, Peruvianus - both normal and monstrous form) Tricho's Tercheckii and Pasacana, some various fero's, some various Cleistocactus and Echinocereus. And a few others that can tolerate the winter months here (which I will give some protection).

[riya]

I would be able to protect from the wet, but not the cold, so I'll look into the possibility of getting one of the high altitude ones/