I'm trying to leave my septic field (drain field, leech field) a wildflower meadow. It's developed a couple good stands of dog fennel (Eupatorium capillifolium) which i like a a screen and -- wow -- the biomass. However, it's not valuable if it clogs the septic drains. I've come to appreciate it's a perennial and that the root crown is probably substantial to regrow each year.
My septic field is in acid red clay, a trench with gravel and perforated black plastic pipe. Previous owners let a tree of heaven get massive at the first turn and we had that removed our first year here along with clearing many other trees, shrubs and vines that got out of control. (eek!) We do put copper sulfate into the line twice a year down stream from the tank. Woods grow up to two of the field borders.
Anyone familiar with the root mass? I've seen other perennial Eupatoriums recommended, and i suppose there are similarities with the tall habit of Joe Pye weed.
The root mass of the Eupatorium tend to be wide spread and shallow so as long as your field lines are at least 18 inches below the surface they should be safe from invasion by the roots of those plants.
The best additive for a septic tank system is bacteria (that's how Ridex works to keep the sludge cleared in a septic tank)
When you add copper sulfate you are actually acidifying the soil where the leachate ends up. (sulfates convert to sulfuric acid and copper, while an important micronutrient, can poison the soil if there is too much build up of copper ions)
With proper bacterial treatments a leach field can actually grow good to eat vegetables since the bacteria will neutralize any pathogens.
This works really well if the soil of the leach field is occupied by a good variety of mycelium which will further convert and destroy pathogens and contaminates.
I appreciate the advice about the tank additives. With a new field, i would not be worried about roots in the pipes. Since we had sweetgum, tree of heaven, mimosa, and a number of other trees growing in the field, and some resprout vigorously from roots, we're putting copper sulfate in the line (after the tank, not in the tank) to make sure all those trees are dead. I agree that's not needed indefinitely.
Living in Piedmont NC, attempting restoration of four acres
You can thank my dental hygienist for my untimely aliveness. So tiny: