Rhubarb is grown for its leaf stems (called petioles) which are thick and fleshy. The stems are colorful—cherry-red to deep red and sometimes green–and tart. They are used in jams and pies—with plenty of sugar added—and are often matched with the sweetness of strawberries.
Rhubarb is a perennial vegetable that requires a dedicated growing spot in the garden for 10 years or more. Rhubarb favors cold winters and mild summers. It may not do well where summers are hot.
Planting Rhubarb
- Rhubarb is a perennial plant that can live for 10 or more years. Choose a location in the garden where one or more rhubarb plants can grow for years. Each plant will require about 4 square feet; rhubarb can grow to 4 feet (1.2m) wide and tall.
- Plant rhubarb in full sun; rhubarb will grow in light shade.
- Rhubarb prefers organically rich, well-worked and well-drained soil; add aged compost and aged manure or commercial organic planting mix to the soil ahead of planting.
- Where the soil is heavy clay, plant rhubarb in a raised bed.
- A soil pH of 5.0 to 6.8 is best for growing rhubarb.
- Rhubarb grows best where winter temperatures fall below 40°F (4.4°C) and summer temperatures do not exceed 75°F (24°C),
Rhubarb Planting Time:
- Rhubarb is a hardy vegetable that prefers cool weather.
- Set rhubarb root divisions (called crowns) in the garden 4 to 6 weeks before the average last frost date in spring or as soon as the soil can be worked.
- Crowns can also be planted in autumn.
- Rhubarb will take a year to begin harvest and four years to come to full harvest so planting time need not be exact.
- Plants can be grown from seed but will not grow true.
- Where summers are hot, stalks will grow thin and spindly; protect plants with shade cloth.
Planting and Spacing Rhubarb:
- Prepare a planting hole 18 inches (45cm) deep and 3 feet wide (.9m); add a handful of bonemeal to the planting hole and fill the hole nearly to the top with a combination of aged compost and aged manure or a commercial organic planting mix then pack the soil in.
- Set the crown or division 1 to 2 inches (2.5-5cm) deep. The growing tip should be angled toward the surface. (The rhubarb root is a rhizome or creeping rootstock; it is a sort of modified underground plant stem.)
- Set container-grown rhubarb plants even with the soil surface.
- Plant crowns or divisions 3½ to 4 feet (1.2m) apart in rows that are 4 feet (1.2m) apart.
Companion Plants for Rhubarb:
- Grow rhubarb with other perennials such as artichokes and asparagus; set aside a growing space for perennials in your garden. Perennial vegetables can grow and produce for 10 years or more.
- You can grow cabbage family crops such as Brussels sprouts, cabbage, and kale near rhubarb, but avoid planting root crops near rhubarb.
Caring for Rhubarb
Watering and Feeding Rhubarb:
- Keep the soil moist but not wet throughout the growing; do not let the soil dry out.
- Make sure that the soil around rhubarb does not puddle in winter to avoid crown rot.
- Fertilize rhubarb beds with aged-manure in autumn and with aged-compost in spring.
- Side dress rhubarb with aged compost at midseason.
Caring for Rhubarb:
- Keep rhubarb beds well weeded. Weeds will compete with rhubarb for light, water, and nutrients. Do not allow perennial weeds to grow near rhubarb.
- Mulch heavily around rhubarb; place a 2-inch-thick (5cm) layer of aged compost around rhubarb during the growing season; compost will help feed rhubarb.
- Where winters are cold cover plants with 1 to 2 feet (.3-.6m) of straw to protect the crowns from freezing; remove the straw in spring when the weather warms.
- To grow rhubarb with longer, thicker leaf stalks; cover the plant with a bottomless box in early spring. The stalks will grow longer reaching for the light.
- Cut flowers or seed stalks as soon as they appear.
- Re-new rhubarb by dividing roots when stems become crowded and thin, usually every 4 or 5 years; replant divisions in another part of the garden. (For more on how to divide rhubarb, see below.)
Rhubarb Pests and Diseases
Rhubarb Pests:
- Rhubarb commonly has no serious pest problems.
- A species of weevil called rhubarb curculio can attack rhubarb. Rhubarb is a host to this pest as is dock, sunflower, and thistle. The adult sucks sap from leaves. A sign that curculio is feeding is oozing sap. Handpick and destroy these weevils.
Rhubarb Diseases:
- Rhubarb generally has no serious disease problems.
- Old clumps may develop crown rot if they sit in wet soil or if they are not divided every 4 to 5 years.
- Make sure the soil is compost-rich and well-drained to avoid crown rot.
- Plants with crown rot should be removed from the garden and placed in the trash.
- Ramularia leaf spot can attack rhubarb. This disease is characterized by circular, brown lesions on both upper and lower surfaces of leaves. Spray plant with compost tea or a fungicide to control leaf spot.
Harvesting Rhubarb
- Rhubarb harvest can begin the second year after planting. Allow plants to establish roots the first year in the garden.
- Harvest just two or three rhubarb stalks the second summer after planting.
- In the spring of the third year after planting, the full harvest of rhubarb can begin when plants are about 3 feet (.9m) in diameter and stems are thick, red, and 12 to 18 inches (30-45cm) or longer.
- Pull stalks from the crown with a sideways, twisting motion. Be careful not to damage the crown. You can also cut stalks away with a sharp knife. Always remove and discard the leaves.
- Stalks harvested in early spring will be the most flavorful; stems harvested later may be pithy.
- Harvest should last 8 to 10 weeks; stop harvesting when the only stems left are short and thin.
- Do not harvest more than one-third of a plant’s stalks in one year. Allow inner stalks to grow on for harvest next year.
- After harvest the remaining stems may die back; once they are brown and withered remove them.
- Do not eat rhubarb leaves which contain oxalic acid, a toxin.
Storing and Preserving Rhubarb
- Rhubarb stalks can be stored in the refrigerator for about one week. Crispness will diminish the longer stems are stored. (Some crispness can be restored by standing stem in a jar of water.)
- Blanched rhubarb can be frozen for 3 to 4 months.
- Rhubarb can be canned or dried.
How to Divide Rhubarb
Rhubarb plants should be divided every 4 to 5 years to keep plants from crowding each other and to give them room to produce thick stalks. When stems stay thin during the growing season, it’s time to divide rhubarb. Divide plants when they are dormant either in early spring or autumn. Here’s how:
- Uproot the plant when it is dormant in early spring or in late fall.
- Cut off the top growth to expose the large crown.
- Cutaway any portion of the root that is shriveled or rotten.
- Cut the crown into pieces—in half or in quarters or more; make sure there are two “eyes” or stem buds and a good portion of root in each of the pieces. Be careful not to injure stem buds during division.
- Plant pieces with two or more eyes to create new plants.
How to Force Rhubarb for Winter Harvest
Rhubarb can be forced to produce new stalks for harvest in winter. Here are two ways to force rhubarb:
- Place a heavy pot or box over the crown in winter. Protected from the harsh cold the plant will send up new stalks seeking sunlight. Stalks can be harvested in 6 to 8 weeks.
- Dig up a crown and expose it to the first freeze in winter. Place it in a pot or box filled with sand, and keep it moist in a place where the temperature stays cold but does not freeze. When you are ready to grow stalks for harvest, move the plant to a place where the temperature is about 60°F (15°C). Keep the plant in the dark or cover it with a 2-foot-high (61cm) box or pot to keep the light out. The plant will grow tall stalks with pale, folded leaves ready for harvest.
Rhubarb Varieties to Grow
Rhubarb stalks will be ready for harvest about 90 days after plants begin growing in spring. Here are popular varieties to grow:
- ‘Chapman’s Canada Red’: heavy stalks are bright red, very sweet, and juicy.
- ‘Cherry Red’: cherry red on outside of stalk, greenish inside cut stalk; very tart and juicy.
- ‘Flare’: stalks are red to green, tart, and sweet flavor.
- ‘MacDonald’s Canadian Red’: dark red stalk, the sweetest rhubarb.
- ‘Valentine’: a sweet, low acid variety that bears early.
- ‘Victoria’: classic heirloom with a tart flavor and green stalks.
About Rhubarb
- Rhubarb is a hardy perennial grown for its edible stalks. The petiole or leaf stem is edible but the leaves and roots are toxic to humans and should not be eaten.
- Stalks grow up from a rhizome or underground stem called a crown.
- Botanical name: Rheum rhaponticum
- Origin: Southern Siberia
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