Ready to grow rhubarb? Follow these tips

Ajay Nair, Patrick O’Malley and Susan Mahr
Rhubarb, a perennial plant, is one of the earliest crops in the garden, once the plant becomes well established. These stems were picked in the first week of May 2020 in Milwaukee.

Rhubarb has long been a popular crop to grow in the home garden. Although usually relegated to the vegetable garden, the large leaves of rhubarb can make a bold statement in a sunny flower bed (there are many ornamental Rheum species as well) and is a great way to incorporate an edible plant into an ornamental planting.

The big leaves provide coarse texture that contrasts nicely with other plants with fine or medium-textured foliage. Try combining rhubarb with ‘Husker Red’ penstemon, tall garden phlox, ornamental grasses, or tall bearded iris.

Rhubarb is very easy to grow. The plants like rich, well-drained soil high in organic matter but are somewhat adaptable. Lighter soils will produce an earlier crop but require more irrigation and fertilization.

Because this perennial will remain in the ground for several years, choose a site in full sun where it can remain undisturbed. Planting on raised beds for good drainage helps prevent crown rot. Prepare the planting site in the fall by eliminating perennial weeds and working in manure, compost or other organic matter. Incorporate fertilizer just before planting in the spring.

Plant purchased crown pieces or divisions from other plantings about 3 feet apart. Set the pieces so the buds are about 2 inches below the soil surface. Don’t harvest any stalks the first year; wait until the second or third year so the roots can establish themselves.

Q: What are the best rhubarb varieties for home gardens?

A: The cultivars ‘Canada Red,’ ‘Crimson Red,’ ‘MacDonald’ and ‘Valentine’ have attractive red stalks and are good choices for Iowa gardens. ‘Victoria’ is a reliable, green-stalked cultivar. Rhubarb plants can be purchased from garden centers and mail-order companies.

Q: Is it safe to eat rhubarb after the plants have been exposed to freezing temperatures?

A: After freezing temperatures, some gardeners express concerns about the edibility of rhubarb. Rhubarb is a tough plant. Temperatures in the upper 20s or low 30s usually cause little or no damage. A hard freeze (temperatures in the mid-20s or lower) is usually required to cause serious damage. Rhubarb damaged by freezing temperatures will have black, shriveled leaves and soft, limp leaf stalks. It’s safe to harvest rhubarb if the plants show no signs of damage two or three days after the freeze event. Damaged rhubarb stalks (blackened foliage and limp stalks) should be pulled and discarded. New stalks that emerge after the freeze are safe to harvest.

Q: My rhubarb plants are blooming. What should I do?

A: The flower stalks should be promptly pulled and discarded. Plant vigor and next year’s production will be reduced if the plants are allowed to flower and set seed.

Flower formation may have been induced by stressful growing conditions, such as drought, extreme heat or infertile soils. Age also may be a factor. Old plants tend to flower more than younger ones. Flower formation can be discouraged by following good cultural practices. Sprinkle one-half cup of an all-purpose garden fertilizer, such as 10-10-10, around each plant in early spring. Stop harvesting rhubarb in mid-June. Water rhubarb plants once a week during prolonged dry periods. Dig and divide large, old rhubarb plants in early spring or late summer.

Q: When should I stop harvesting rhubarb?

A: Gardeners should stop harvesting well-established rhubarb plants in mid-June in Iowa. Continued harvest through the summer months weakens the rhubarb plants and reduces the yield and quality of next year’s crop.

Early spring is an excellent time to transplant rhubarb.

Q: When can I transplant or divide rhubarb?

A: Early spring is an excellent time to transplant rhubarb. As soon as the ground is workable, carefully dig up the plants in early spring before growth begins. Dig deeply to insure getting a large portion of each plant’s root system. Large rhubarb plants can also be divided. Divide large clumps with a sharp spade or butcher knife. Each section (division) should have at least two or three buds and a portion of the root system.

Replant the rhubarb as soon as possible. The roots must not be allowed to dry out prior to planting. If the rhubarb can’t be planted immediately, place the clumps in a plastic bag and store them in a cool, dark location. This temporary storage should be fine for a few days.

Rhubarb is easy to grow. It performs best in full sun. Avoid shady sites near large trees or shrubs. Rhubarb also requires fertile, well-drained soils that are high in organic matter. Sandy and clay soils can be improved by incorporating large quantities of compost or other forms of organic matter into the soil before planting.

When planting rhubarb, place each section upright in the planting hole with the buds 1 to 2 inches below the soil surface. Space the plants about 3 feet apart. After planting, water thoroughly. Continue to water the plants throughout the first growing season. During dry weather, a deep soaking every seven to 10 days should be adequate.

Rhubarb also can be transplanted in early fall (mid-September to early October). Mulch fall planted rhubarb with several inches of straw in mid-November.

Q: When can I start harvesting newly planted rhubarb?

A: After planting rhubarb, it’s best to wait two years (growing seasons) before harvesting any stalks. The two-year establishment period allows the plants to become strong and productive.

Rhubarb can be harvested over a four-week period in the third year. In the fourth and succeeding years, stalks can be harvested for eight to 10 weeks.

Best uses for rhubarb

Rhubarb is typically used for jam, sauces, or in pies or other desserts but it also works well as an accompaniment to savory foods. Because rhubarb is tart it almost always needs to have sugar added to make it palatable.

Rhubarb is most tender and flavorful in spring and early summer but can be used throughout the season. Select firm, crisp stalks when they are 8 to 15 inches long. To harvest, twist off the leaf stalk at the soil line and cut off the leaf. Do not harvest more than a third of the leaves in any year to keep the plant going strong (and don’t pull any leaves during the first year of growth).

On young plants, pick stalks only in the spring and allow them to grow unpicked all summer or growth will be delayed the following spring. You can harvest sparingly on vigorous, well-established plants throughout the summer. Any leaves remaining at the end of the season can be pulled just before the first fall frost.

Store fresh rhubarb stalks unwashed in the refrigerator for up to two weeks. It will keep it the freezer for up to 6 months.

Nair and O'Malley are horticulturist specialists from Iowa State University Extension and Outreach while Mahr or University of Wisconsin Madison is the coordinator for the state's Master Gardener program.