This extremely old (and downright unpleasant) myth stems from the fact that there is plenty of nitrogen in urine – nitrogen being something that your plants need. However, given the fact that you already give your plants all the nitrogen they need through other means, peeing on them is totally unnecessary. Not only this, but unless you were to actually test the nitrogen content of your pee each time before using it, you could end up giving your plants a dangerous overdose.