Q: We have a septic tank in the back yard. I want to plant some Leyland cypress, for screening, and a dogwood for its flowers nearby. How close to the tank can I plant them?
A: Septic tanks and their pipes are not constructed to keep tree roots out. If you plant a shrub or tree near enough, eventually the roots will plug a line and cause problems. For trees like you are contemplating, plant them no closer than fifteen feet from the tank or to a drain field supply line. If your situation demands that they be closer, you’ll need to dig a deep trench two feet from the tank or lines and install aluminum flashing edgewise into it. Once the flashing is in place, fill the trench with soil. Use sixteen inch wide flashing and let an inch of it show above ground to prevent roots from getting over it.