In order for rhubarb to become well established, stalks should not be harvested the first year and only a few the second year. This allows the plants to become acclimated to the garden site and to store nutrients for further healthy growth. From the third year on, rhubarb can be harvested in late May and throughout June in the Midwest . Stop harvesting rhubarb when the plant begins to produce slender stalks.
Never harvest more than one-third to one-half of the plant stalks, in order to preserve enough foliage to continue to feed the plant. The stalks are tastiest when fairly young, so harvest them soon after the leaf expands. Harvest by grasping each leafstalk near the base and pulling it slightly to one side. Be sure to harvest before seed heads form.
Fresh rhubarb can be stored for two to four weeks in the refrigerator. For freshest results, store in perforated bags in the crisper. Be sure to not eat the leaves, only the stalks.
After the last harvest, usually in early July, the rhubarb plants should be allowed to grow until killed by frost.
Rhubarb leaves should be added to your compost pile. The leaves will rapidly decompose, or can be used as a mulch to shade other plants roots.
For more information on growing rhubarb, please see http://www.almanac.com/plant/rhubarb.