In my experience a barrier did no good, and in some ways made matters worse. It prevented the roots of vegetables from penetrating the sand beneath and so the bed dried out more quickly, but it did not prevent the roots of nearby trees and bushes from eventually growing up into the bed and making it dry out more quickly still.

Nematodes still invaded the beds. From what I understand, nematodes do not enter the bed from below, but from the top. If any nematode infested soil is added to the bed, they spread through out the bed. Garden tools contaminated by a bit of nematode infested soil on them, or even birds pecking around, can spread the nematodes from bed to bed.

Bill

A barrier, as Bill said, will do little to prevent nematodes, weeds, and other undesirables from entering the bed.

Make them as deep (high) as you can, building up the edges either with boulders or mulch.

thanks for the help, bill and "fawnridge".

i'll try a higher bed and nix the barrier and read up some more on organic gardening in florida.

andrea