One of spring’s garden harbingers, rhubarb stems burst through soil early in the growing season. The tart, colorful stems grace pies and jams with tangy flavor that is typically tamed with sugar or teamed with sweet strawberries. Rhubarb adds sculptural beauty to the garden with its blocky stems and large leaves. While leaves offer textural beauty, they’re not part of the harvest package. Rhubarb leaves contain high concentrations of oxalic acid and shouldn’t be eaten. When growing rhubarb, harvest the stems, then remove leaves and add them to the compost pile. Rhubarb grows best in zones where the ground freezes in winter. Plants require an extended chilling period with temperatures below 40 degrees to produce a crop of stems. As a result, rhubarb is commonplace in gardens throughout the coldest sections of the country, although it can be grown as far south as Zone 7.
Soil, Planting, and Care
A true perennial, rhubarb plants can yield harvests 5 to 8 years or longer. Once plants are established, they don’t transplant easily, so choose your planting site carefully. Rhubarb thrives in full sun but will yield to light shade. Select a location that gives plants ample room; individual rhubarb plants can measure up to four feet wide and tall.
Plant crowns in spring as soon as soil is workable. Tuck plants into slightly acidic soil rich in organic matter; blend in plenty of well-rotted manure or compost, or amend the soil with Miracle-Gro® Garden Soil for Vegetables & Herbs. Rhubarb crowns require shallow planting (around 4 inches deep), but because plants are such heavy feeders, you should dig planting holes at least a foot deep. If your soil is heavy clay, you may want to consider planting rhubarb in raised beds filled with soil designed especially for that kind of growing environment, such as Miracle-Gro® Raised Bed Soil.
Water newly planted crowns, and keep soil moist throughout the growing season. As summer heat arrives, mulch plants with a 2-inch-thick layer of organic mulch, such as compost, straw, or shredded bark. Replenish mulch throughout the growing season as needed to maintain 2-inch thickness. Fertilize at planting and every couple of weeks throughout the growing season with Miracle-Gro® LiquaFeed® Tomato, Fruits & Vegetables Plant Food.
In fall, when stems die back, remove all plant debris. Mulch plants after the ground freezes, covering crowns with 2 to 4 inches of compost or leaves.
Established plants need to be divided every 5 to 10 years. You’ll know it’s time to divide when stems are crowded and thin. Divide when plants are dormant, in early spring or fall. Dig and lift clumps, cutting roots into pieces about 2 inches across. Take care not to damage the buds on the top of each root section. Replant the best sections.
Few problems plague rhubarb. Crown rot settles in when soil drainage is poor. This disease damages terminal buds, which results in spindly, weak stems. The cure is to dig out and burn infected plants. Don’t replant rhubarb in areas where crown rot has damaged plants before.
Leaf spots can attack the plant, with the worst being red leaf, or Ramularia, which can ruin the stems. Cut away old foliage in fall to help prevent leaf spot, whose spores overwinter in the debris.
Rhubarb curculio occasionally attacks plants. Insects puncture leaf stalks from late spring to early summer as they feed and lay eggs. Damaged stems ooze sap and may begin to decay.
Harvest and Storage
Forget harvesting the year that you add rhubarb to the garden. In the second year after planting, harvest lightly, removing only a few stalks from each plant. From the third year on, harvest stems freely. To ensure continued production, take care not to remove more than one-third to one-half the stalks from any one plant during any one harvest.
To harvest, choose stems that are 12 to 18 inches long and reddish in color. Grasp the stalk near the base and pull it upwards, twisting the stem as you pull. You can also use a sharp knife to slice stems from the plant. Cut as close to the crown as possible without damaging it. After harvesting, remove the leafy portion and the base of the stem, leaving only the colored stalk.
Early spring stems offer the most flavor and tenderness; they’re ideal for pies. Stems harvested later in the season are often pithy. Reserve these stems for stewing, sauces, or jams.
Stop harvesting as stems get shorter and thinner. At this point, plants are storing up energy for next year’s harvest. Mature plants typically provide an 8- to 10-week harvest. In general, expect 2 to 3 pounds of stalks per mature plant per season.
For the best quality in cooking or freezing, use freshly harvested stalks. If that is not possible, keep cut stems up to 1 week in the refrigerator, although crispness diminishes with storage. You can refresh crispness by standing stored stems in water before using; however, the flavor will be slightly diluted. You can also chop stems and freeze the pieces in a plastic freezer bag for much later use.
I planted rhubarb this spring. When can I start picking?
The rule of thumb is not to harvest rhubarb the year you plant it. Give plants time to produce a sturdy root system. The second year after planting, pick only a few stems from each plant. By not picking heavily, you’re allowing leaves to generate energy that enhances root growth. The third year is when you can start picking rhubarb by the armload.
White stalks are rising out of the center of my rhubarb plants. What are they?
Those stalks are the flowering stems. Remove them as soon as they appear. Allowing rhubarb to bloom takes energy that the plant might otherwise shift toward root growth, which will help fuel next season’s harvest.
How do I know when rhubarb is ready to pick?
Look for reddish stems 12 to 18 inches long. Smaller diameter stems offer best quality. Larger, fatter stems can be pithy and tough, especially later in summer and also if plants experience drought.
How do I harvest rhubarb?
Grab stems near the base and pull gently while applying a slight twisting motion. Take care not to injure the central bud, which will yield many more stems in the course of the growing season. Harvest up to one-third of stems from one plant at any one picking.
Can I harvest stems from a mature rhubarb clump all summer?
As long as clumps do not flower, you can continue to pick stems well into summer. Stop harvesting when stalks remain small and short. From this point on, the plants are storing energy for next year’s harvest season. Keep rhubarb well watered until frost.
My rhubarb was growing fine, then stalks began to fall over and rot. What is happening?
You’re dealing with crown rot, a fungus disease that sometimes attacks established clumps of rhubarb, especially those that need dividing. Once it attacks a plant, you’ll need to dig it up and destroy it. Do not re-plant rhubarb in the same spot where crown rot has affected a plant. The best way to avoid crown rot is to plant rhubarb in well-drained soil. Raised beds also help, as does dividing clumps when necessary.
My rhubarb patch is so healthy that plants are crowding one another. Can I divide them, and if so, when?
Many gardeners divide rhubarb every 4 to 5 years. You’ll know it’s definitely time to divide when stems are short, stringy, and dry. Use a sharp spade to slice a start from a rhubarb crown in early spring, before growth begins. Dig up as much root as possible. Divide the clump so that starts each have two buds. Plant buds 1 inch below the soil surface. If possible, try to leave the part of the original plant undisturbed, so you’ll be able to harvest from it this season.