Originally posted by TCLynx on AGC, June 14, 2010
The common recommended minimum depth for flood and drain gravel beds is 1 foot deep. Some people do attempt beds less than that but the effective bio-filter in a shallow bed is more limited and managing flood and drain by siphons becomes farm more difficult with a shallow bed.
I’m now a very big proponent of Deep grow beds. Many of my grow beds are now 24 inches deep rather than just 12. I’ve discovered that the 100 gallon rubbermaid stock tanks are only a couple dollars more than a 50 gallon tank. And with a 100 gallon tank simply setting it on some concrete blocks makes it a nice height and it can still drain into a sump tank that is sticking up out of the ground about 8 inches.
So what if the bottom few inches don’t drain completely, the bed is 24 inches deep. Even if the bottom 6 inches don’t drain and the top 2 inches stay dry, I still have far more effective bio-filter depth than a 12 inch deep grow bed of the same total volume. I’ve found that the deep grow beds are very good at filtering solids. And with deep beds aquaponic trees are an option.
If you find that with deep grow beds you have plenty of filtration but not enough plant space for nutrient removal, it is fairly easy to add some supplemental plant space using the clean water from a clean water sump to feed say a seasonal NFT pipe set up or raft bed if you see the need.