Improving Blackwater Tank Plant Growth

Hi everyone! I just set up a new 5 gallon blackwater tank I'm going to let it cycle (to the extent that a tank whose PH is going to be in the 4's or 5's will cycle) for a month before I add a light or any plants...which brings me to my question; what can I do to improve plant growth in a blackwater aquarium? Would it be possible to fertilize plants at the roots to limit the effect the ferts would have on the tank's conductivity levels? I would like to keep the conductivity no higher than about 70 microsiemens, and would prefer to keep it below 40 microsiemens if possible. The substrate is peat moss and leaves capped with sand, and the tank's conductivity when I set it up was about 15 microsiemens. Thanks