Rhubarb

Rhubarb (*Rheum × hybridum*) is a hardy herbaceous perennial grown for its thick leaf stalks. It survives cold winters, dies back to its crown in autumn and sends up fresh leaves each spring. A mature plant is imposing, often forming a clump at least 1.5m wide, but it then crops reliably for many years with relatively little routine maintenance.

The stalks range from green flushed with red to vivid ruby, depending on variety and growing conditions. They are usually harvested in spring and early summer, then cooked for desserts, chutneys and savoury sauces. Rhubarb is botanically a vegetable even though it is often used like a fruit. Only the cooked leaf stalk is edible: the leaf blade is poisonous and must be removed, although discarded leaves can be composted because their oxalic acid breaks down during decomposition.

Patience at establishment gives stronger long-term plants. Do not harvest stalks in the first year after planting. Take only a few in the second year, then begin normal harvesting in the third. Even on an established crown, never remove more than about one-third of the stalks at one time, because the remaining leaves must replenish the crown.

Rhubarb may be raised from seed, but named cultivars are normally bought as potted plants or dormant bare-root crowns. Seedlings take longer to establish and vary from their parents, whereas divided crowns reproduce a cultivar exactly. Buy healthy virus-free stock from a reputable supplier.

Cultivars differ in stalk colour, sweetness, flavour, vigour and harvest season. Select an early cultivar for forcing and a compact one if container space is limited. An RHS Award of Garden Merit identifies cultivars that performed well in trials, but site, care and intended harvest period still matter.

Recommended varieties

Rhubarb ‘Victoria’

A reliable old late-maincrop cultivar with mid-sized green stalks flushed red and a robust flavour. It is productive, begins cropping from late May and is suitable for late forcing.

Cultivar sourceAllotment Pro variety guide

Rhubarb ‘Fulton’s Strawberry Surprise’ AGM

A vigorous maincrop cultivar producing bright-red stems with a balanced flavour. It is normally ready during May and June.

Cultivar sourceAllotment Pro variety guide

Rhubarb ‘Raspberry Red’ AGM

A prolific early cultivar valued for heavy crops of sweet, rich-red stems without forcing. Harvesting can begin in April and continue into June, and established crowns can also be forced.

Cultivar sourceAllotment Pro variety guide

Rhubarb ‘Timperley Early’ AGM

A high-yielding first-early cultivar bred for forcing but also productive outdoors. Its thick stalks are deep red at the base, becoming light green with red flecks, with green flesh.

Cultivar sourceAllotment Pro variety guide

Choose an open sunny site with fertile, moisture-retentive soil that drains freely. Light shade is tolerated, but avoid waterlogged ground and frost pockets where emerging shoots may be damaged. On heavy clay or a poorly drained plot, use a raised bed or large container rather than allowing the dormant crown to sit wet through winter.

Remove perennial weeds before planting. Dig in about two bucketfuls of well-rotted garden compost or manure per square metre. In a no-dig bed, place a settled organic mulch over the surface before planting into it. Rhubarb will occupy the position for years, so thorough preparation is more useful than trying to correct compaction or poor drainage later.

For container growing, use a pot at least 50cm wide and 50cm deep with ample drainage holes. Fill it with a peat-free, soil-based compost, which holds moisture and remains structurally stable longer than a light multipurpose mix. A container-grown crown needs more frequent watering than one in open ground and should never stand in a tray of water.

To raise plants from seed, sow indoors in late winter in modules of peat-free seed compost. Place seed 2.5cm deep and grow seedlings on before planting outside in late spring or autumn. Alternatively, sow 2.5cm deep in a prepared outdoor seedbed in spring. Thin seedlings first to 15cm apart, then transplant the strongest to their permanent positions at 75–90cm spacing. Seed-grown plants are variable and slower to reach cropping size.

Potted plants can go into suitable ground at most times of year, although spring and autumn are preferable; avoid very hot, dry weather. Dormant bare-root crowns are generally planted from November to March and should be set promptly after delivery.

Dig a hole slightly wider than the root system. Set the plant so the crown tip, or the point from which leaf stalks emerge, remains just above soil level. Backfill, firm gently and water thoroughly. Space several crowns 75–90cm apart. In a container, use the same planting depth, leaving the main growth bud just above the compost surface.

Water new plants regularly during dry spells throughout their first growing season. Once established in open ground, rhubarb usually needs watering only during prolonged summer drought, when growth may otherwise slow or stop. Container plants require regular attention throughout active growth. Keep compost evenly moist but never saturated, because waterlogging encourages root and crown rot.

In spring, spread a 7cm layer of well-rotted organic matter around each plant. Leave the crown exposed rather than burying it under mulch. This treatment conserves moisture, suppresses weeds and usually supplies adequate nutrients. If growth remains poor on infertile soil, an organic high-nitrogen fertiliser in spring or summer can boost foliage, but excessive nitrogen may encourage flower stalks.

Remove flowering stems at their base as soon as they appear so they do not weaken the crown. Flowering is more likely in seed-raised plants, wet summers, overfed plants and old congested clumps. Allow ordinary foliage to die down naturally in autumn, then cut or pull away the dead leaves. Exposing the buds to winter cold helps trigger the next spring’s growth; established plants need no other winter protection.

Forcing produces earlier, paler, sweeter and more tender stalks. In midwinter, cover a strong established early cultivar with an opaque forcing jar, tall bucket or dustbin. Excluding light blanches the new shoots. Check regularly once they appear and harvest four to eight weeks after covering. Remove the cover after the first flush and allow later stems to grow normally. Do not force the same crown in consecutive years.

For an even earlier crop, lift roots in November and leave them outside for up to two weeks so cold can break dormancy. Pot them in peat-free multipurpose compost, move them into darkness at 7–16°C and keep the roots only slightly moist. Stalks are often ready in about five weeks. This treatment severely weakens the lifted crown, which is normally discarded after harvest.

Divide a healthy mature clump about every five years, especially when it becomes crowded or loses vigour. While it is dormant from mid-autumn to early spring, lift the whole clump and cut it into sections. Each division must retain part of the thick rhizome and at least one sound growing bud. Outer sections are usually stronger than the old centre. Discard decayed material and replant divisions immediately, or wrap them briefly in damp sacking until their new sites are ready.

Do not take any stems in the planting year and harvest only sparingly in year two. From the third year, most cultivars crop from April or May. Stop the main harvest in late June or early July, even if stems remain edible, so enough foliage can rebuild the plant for the following year.

Choose a young stalk about 30cm long whose leaf has just fully opened. Grip it low down, then pull and twist gently so it releases cleanly from the crown. Do not cut it or leave a broken stump, which can rot. Remove the poisonous leaf blade immediately and compost it. Take no more than one-third of the plant’s stalks at once.

Harvest forced stalks at about 30cm, usually four to eight weeks after covering. When the forced flush is finished, uncover the crown and do not harvest it again until the following year. Rhubarb is best used fresh, but sound stalks keep in a refrigerator for a couple of weeks and also freeze well.

Rhubarb is generally robust, but slugs and snails can damage tender young shoots, especially beneath forcing covers. Late frost may scorch new growth, so protect it temporarily with straw or biodegradable fleece when freezing weather is forecast. Split stalks can follow frost or erratic growth when cool or dry conditions are followed by mild wet weather.

Rot is most likely in damp, waterlogged soil or containers left standing in water. Improve drainage and cut out a small affected area promptly before decay spreads. Weak, discoloured or distorted growth may indicate a virus; buy clean stock and divide only vigorous symptom-free plants.

Common problems