Only the stalks of rhubarb should be harvested for eating, not the leaves. The leaves contain poisonous compounds and should be removed completely. In terms of pruning, rhubarb should be cut back in late fall or early spring before new growth appears. Cut back any dead or damaged stems at the base, and trim off any small stems or shoots to allow the larger ones to grow. Do not cut back more than one-third of the plant, as this may harm its ability to produce new stalks.