Well the general rule in container gardening is that the containers must have some form of drainage. Otherwise the water collects in the bottom, you get ponding of the water, bacterial growth, and root rot. I can't really picture containers made from "wire forms and concrete". That would be quite unusual IME but I would be worried about that weight on the field interfering with drainage in the field. Given all the drainage problems and shallow drain fields one reads about in many parts of Florida, especially with sandy soil, I'd be very reluctant to alter my septic drain field at all. And there are literally thousands of lightweight containers with drainage holes available for gardeners to use that can be easily moved and adjusted for sun exposure without creating problems for the filed. Unlike in-ground gardening Container Gardening has its own set of unique needs so I'd suggest some in-depth reading over on the Container Gardening forum here. Dave

generally deep fibrous rooted native meadow plants are recommended over septic fields because they can improve the seepage capacity of the soil. i just posted this same statement on another thread - was that yours?... in the past it was a concern to stay clear of deep "tap" rooted plants but its been found thats as much of a problem as they thought it would be... www.prairienursery.com has a seed mix specifically designed for septic fields.

Before you plant, I'd amend the soil so that whatever you put in has the best possible chance. We actually have rough field grass over ours (which is situated in our back field.) It's easy to cut the sod and just flip in up en mass when the tank needs pumping, and it seems to survive as well as the rest of the field, but I can't remember exactly how many inches of soil we have over our tank. Whatever plant you put there, it needs to be something that can either function like sod and be removed and put back in just one or a few pieces, or something that you don't mind having to replace every time the tank gets pumped. I would think that something like a juniper which is woody and prickly to handle would not be a good choice. Do you have a photo of where it is in your yard? You might get more suggestions with that to get ideas flowing. For instance, is it somewhere you could develop a perennial bed and put a half-buried fake rock that you could plant around with tall perennials or fountain-shaped shrubs like forsythia nearby to spill over and largely hide it, and then remove the "rock" when pumping time arrived (preferably scheduled for a time of year when the perennials would have died back and a shrub could be tied back without damage)? Is it somewhere that hardscaping would be appropriate, whether it would be a piece of moveable yard ar*t, a birdbath or fountain, or a path, a patio, etc where you could put a large tile to be lifted when needed? Another plant that could be placed directly over it in a flower bed (like the thyme suggestion) would be one of the low-growing sedums, but neither thyme or se*dum would be able to compete well with grass in a lawn setting.

Measure diameter of hole and multiply by 3.5. Cut a piece of flexiable plastic or heavy cardboard or metal roof flashing long as number found above X twice the thickness of tank cover. Work strip to snuggly fit inside tapered hole making sure lower edges line up ( top edges will miss-alighn where they meet but it doesn't matter.) Use duct or other strong tape to join ends. Wax inside ring and set on waxed plywood. Fill ring 3/4trs full of sackcrete and bury wire reinforcmet and handle in it before it sets. You might have to lightly agitate concrete to make sure ring form is round. Many people just lay flat rot resistant material over the hole which seems to work fine.