Rhubarb buds might be my favorite sign of spring. Native to Siberia and introduced into North America by European colonists in the 1700’s, Rheum rhabarbarum is a versatile perennial that kicks off the growing season. Once it’s ready to harvest, you’ll be rewarded with attention-grabbing tartness and fresh, grassy flavor. Varieties have red or green stalks, but all are delicious. In this article, I’ll discuss how to grow rhubarb plants, optimize yields, and use it in delicious desserts and side dishes.
Remember that rhubarb leaves are poisonous. Oxalic acid is the main toxin in this plant. Practically speaking, you would have to consume more than a pound of leaves to endanger your health, but it’s best to be careful. Here’s a description of oxalic acid poisoning from the National Institutes of Health. Symptoms include burning and blisters in the mouth and an upset stomach. If you suspect oxalic acid poisoning, do not induce vomiting and call Poison Control at 1-800-222-1222.
Planting
Crowns are the easiest way to start rhubarb plants. A rhubarb crown is located just beneath the soil surface; the stalks and roots emerge from a crown. These can be purchased bare or in pots. It’s fine – maybe even preferable – if potted crowns have a stalk or two already emerging. Large crowns from well-established plants can be divided and propagated, as discussed below. Plant crowns early in the spring, as soon as the soil can be worked.
Before planting, prepare the soil. A soil test is always a good idea, to ensure sufficient nutrient levels. Results from a soil test will also reveal if soil pH should be adjusted. Aim for a slightly acidic pH, between 6.2 and 6.8. The Virginia Tech soil testing lab will provide amendment recommendations with test results. Finally, add compost to optimize soil quality. Rhubarb grows best in well-drained soil with plenty of organic matter. For Virginia clay, a good rule of thumb is to work 4 inches of compost into the top 12 inches of soil. That’s a lot of compost and a fair amount of work, but it will be worth it.
When planting, dig holes deep enough so that the buds on crowns will be 1 to 2 inches below the surface of the soil. If planting crowns from pots, soil level in the garden should be the same as the soil level in the pot. Space the holes 3 feet apart, in rows that are 5-6 feet apart. Place crowns in holes with buds pointing upwards, then backfill. Scatter a handful of 10-10-10 fertilizer around each planting site. Water thoroughly, but not excessively.
Rhubarb can also be started from seed. One advantage of this approach is that more varieties are available from online or catalog sellers. The disadvantage is that it can take an extra season before the plants are vigorous enough to harvest. Start seeds indoors, 5 or 6 weeks before the last frost. Harden off the seedlings after danger of frost is past, then plant as described above.
Cultivation
Climate is probably the main challenge when growing rhubarb in Virginia. Rhubarb grows best where summers are relatively cool, with an average temperature of 75℉. Rhubarb crowns also require 500 hours of temperatures below 50℉ to stimulate stalk growth. Virginia winters are usually cold enough, but summers can be problematic. If possible, choose a site with afternoon shade. If this is not an option, consider using “shade cloth” to keep plants from overheating.
Otherwise, growing rhubarb is pretty easy. Irrigate, so that soil stays moist, but do not over-water, as this can lead to crown rot. Mulch, such as straw, will help maintain soil moisture. Fertilize established plants in early spring with 20 lbs. of 10-10-10 fertilizer per 1000 square feet of bed. After harvest, side-dress with 2 lbs. of ammonium nitrate per 1000 square feet.
Vigorous plants will form flowering stalks. These stalks are round in cross-section (see photo above), as opposed to the oblong-shaped leaf-bearing stalks that we eat. Remove flowering stalks as soon as they appear, or they will divert energy and nutrients from crowns and leaf-bearing stalks.
Dividing crowns
Rhubarb crowns should be divided every 5 to 6 years. A crown is ready to divide when the stalks emerge around the outside of the crown, not in the middle (see picture).
Divide crowns when plants are dormant, in late winter or early spring. Dig around and under each crown, about a foot down, to separate it from its roots. Pull crowns out of the soil and brush or wash them off. Using a sharp spade or knife, cut into chunks with 2-3 buds each. Remove and discard any soft or rotten bits. Replant as described above.
Diseases and pests
Crown rot is the primary disease that infects rhubarb. The major symptom is wilting of stalks and leaves, followed by rapid collapse and death of the whole plant. Water-soaked spots may appear at the base of stalks. Phytophthora causes most crown rot, though Pythium, Rhizoctonia and Botrytis can also be at fault. Regardless, the only solution for crown rot is prevention, because crown rot can’t be halted once it sets in. To avoid crown rot: 1) maintain good drainage by incorporating plenty of organic matter in the soil; and 2) do not over-water. As mentioned above, mulch is a great way to keep soil moist without adding too much water.
The major pest is the rhubarb curculio, sometimes called the rhubarb weevil (Lixus concavus). This cute little bug is about ½ inch long, with a long, curved, flat-ended snout (see picture). The curculio is brown or rust-colored, but it’s often covered in yellow pollen. Curculios don’t actually eat rhubarb, but they punch holes in stalks and crowns to lay their eggs. These holes leak sap, reducing the plants’ vigor and promoting fungal diseases. Prevent rhubarb curculio infestation by keeping beds clear of curly dock (see picture), a weed that happens to be their preferred food source.
Harvest
In the first year after planting crowns or seedlings, don’t harvest rhubarb at all. In the second year, harvest only 2 or 3 times, spread out over 4-6 weeks. In subsequent years, harvest 3-5 times over 8-10 weeks. A general rule is not to harvest more than about ⅔ of the stalks at once. If new stalks are very skinny or pencil-sized, stop harvesting.
Harvest stalks after their leaves are fully grown, usually when they’re smooth, not crumpled. Do not cut the stalks because the cut ends can let rot-causing pathogens into the crown. Instead, grab a stalk at the base, then twist and pull upwards. It might be necessary to rock the stem back and forth a couple times to loosen its connection to the crown. The attachment point should be visible at the bottom of the harvested stalk, and will look like the bottom of a celery stalk.
Cut the leaves off the stalks as soon as possible to delay wilting. It’s okay to compost the leaves, but be sure that pets and children can’t get to them, due to their toxicity.
Rhubarb will go dormant in summer heat, particularly in warmer zones, but it may resume growing when cooler weather returns. Feel free to harvest judiciously at this point, as described above. Rhubarb is delicious in the fall too, particularly along with apples.
Storage
Of course, rhubarb is best enjoyed fresh, but it can be stored in the refrigerator for a couple of weeks. This is especially important when waiting for strawberries to ripen. Wrap stalks in aluminum foil (moderately tightly), but don’t crimp the foil. Keep in a “crisper” drawer of the refrigerator. The goal is to keep the stalks moist, while preventing buildup of ethylene gas that will make them go soft.
Rhubarb also freezes well. Wash and dry the stalks, then cut them into 1-inch pieces, seal in a plastic bag, and place in the freezer.
Cooking
Recipes featuring rhubarb are plentiful in books and online. Classics like the “Joy of Cooking” are my go-to sources. Here are a few of my favorite ways to prepare rhubarb:
∙ Cobbler, alone or with strawberries or apples! This works well covered with cornmeal biscuits.
∙ Pie, with or without strawberries or apples.
∙ Compote (chopped rhubarb cooked down with sugar to a sort of jelly), which is great as an ice cream topping. Also delicious in place of, or along with, strawberry shortcake and whipped cream.
∙ Roasted: Cut into chunks and toss with sugar and maybe some spices, such as cinnamon, vanilla bean seeds, or cardamom. Then roast at 350℉ for 25-30 min.
∙ Savory – really! Great side dish for beef, roasted with red wine (and a little sugar).
References and Further Reading:
Featured photo: Rhubarb stalks by Jeremy Keith, CC BY 2.0
Growing rhubarb in home gardens University of Minnesota Extension
Rhubarb (Publication 438-110) Virginia Cooperative Extension
Rhubarb in Home Gardens University of Tennessee Agricultural Extension Service
Rhubarb, Rheum rhabarbarum Wisconsin Horticulture Division of Extension
Will that plant grow here? North Carolina Cooperative Extension
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