With any current flow either way and the roots at a differnt level , It may kill the plants.
And with out a control of volts and amp, plus a meter.
Remember any loose volts will cause electrolicis (sp) to ground and make you pipes in the house leak.
So you must use high resistive insulation, any millivolt losses will eat pipes and metal parts.
Due to changes in the conductivety when wet and dry you will need a contoler , in the millivolt range.
Remember low levels of copper will kill plants, and they will absorb copper for normal groth in the ppb levels ,, thats parts per Billion
Have seen some good power supplies for under $1000 U.S.
With out data of Volts , amps ,time
I wish you the best of luck May OHM'S be you guide
Note had a shorted pump once, and did not effect the plants, but I did get knocked on my ass once. OHMS OHMS, O lord I feel the power.
Next you may want to try the Magnitic thing from mgausse the M gause NN,SS, NS orientation. North,south off axis orentation. (I tried that no luck )
With out a base line of grams/watts/month , you will need to establish.
Have fun