An attractive perennial plant with large, showy leaves, rhubarb (Rheum x cultorum) is grown for its red, pink or greenish-pink stalks that add a tangy flavor to desserts and sauces. This cool weather plant grows in U.S. Department of Agriculture plant hardiness zones 3 through 8. If you're short on garden space, you can grow the versatile rhubarb plant in a large container.
As a large-rooted plant, rhubarb requires a sturdy container with a minimum depth and width of at least 20 inches. The larger the container, the more the plant can expand and grow. The type of container isn't important, as long as it has at least one drainage hole in the bottom. Without drainage, the plant is likely to succumb to root rot and die. Fill the container with a lightweight, well-drained potting mixture such as a good quality commercial potting soil.
Plant rhubarb crowns, available from garden centers or from dividing an existing plant, in early spring. Planting rhubarb in containers is basically the same as planting it in the ground. Dig a hole in the potting mixture and plant the crown 1 to 3 inches deep. Unless you use a very large container such as a whiskey barrel, limit planting to one plant per container because the rhubarb requires room to spread. Place the container in full sunlight.
Water and Fertilizer
Rhubarb grown in containers requires frequent watering during warm weather. Water the plant until water trickles through the drainage hole, whenever the top of the soil feels dry. Check the rhubarb often -- the plant may require water every day during hot, dry weather. Water with a hose near the soil to keep the leaves as dry as possible. A 1- to 2-inch layer of mulch, such as bark chips or grass clippings, helps keep the roots cool and moist.
Although rhubarb grown in the ground requires no fertilizer, rhubarb in containers benefits from regular feeding, because the roots can't absorb nutrients from the soil. Fertilize the plants every year before new growth emerges in early spring. Apply 1/2 cup of 10-10-10 fertilizer on the soil around each plant, and then water deeply and rinse off any fertilizer that accidentally lands on the leaves.
Allow newly planted rhubarb to mature until the second year, because harvesting before the plant is fully established reduces plant vigor and yield. Remove blooms that appear in spring to direct the plant's energy to the development of stalks. Cut back old stalks after the leaves die down in autumn. Surround the plant with 2 to 3 inches of mulch or compost to protect the roots, but leave the buds and crown exposed; rhubarb requires a period of winter chill. Divide the plant every five to six years to keep it healthy and vibrant.
Rhubarb stalks are safe to eat. However, the leaves contain oxalic acid, a substance that is poisonous when ingested. Symptoms may include burning in the mouth, stomach pain, diarrhea, nausea and vomiting. The leaves cause no problems when added to the compost pile. Place the container rhubarb out of reach of small children and curious pets.