Rhubarb is a useful crop for anyone who enjoys crumbles, compotes or a sharp fruit-style sauce. Although it is cooked like fruit, the edible part is the leaf stalk of a hardy perennial vegetable. Once established, a rhubarb crown can return year after year with relatively little attention. The most common beginner's mistake is picking heavily before the plant has developed the root reserves it needs.
Give rhubarb a permanent place, good soil and time to establish. It will reward you with spring harvests for many years, but it is not the right crop if you expect a substantial yield within weeks of planting.
Choose a position with room to spread
A mature rhubarb plant produces enormous leaves and may eventually occupy a space well over a metre across. Don't squeeze a crown between two closely spaced vegetables and expect it to remain compact. Plant it where you can reach the stalk bases without trampling surrounding beds.
Rhubarb grows best in fertile soil that holds some moisture but drains adequately. A sunny position is useful, although some varieties tolerate partial shade. It doesn't thrive in permanently waterlogged ground. A neglected corner under trees is also a poor choice, because large roots compete for food and moisture.
Prepare the site thoroughly. Remove perennial weeds and work well-rotted garden compost into poor soil. Because the plant may occupy that patch for a decade or longer, taking an afternoon to improve the ground at the beginning is time well spent.
Should you plant crowns, potted plants or seeds?
Most gardeners buy rhubarb as a dormant bare-root crown or a young potted plant. A crown is a section of established rootstock with buds ready to produce shoots. This is a faster, more predictable start than sowing seed.
Bare-root crowns are commonly sold from autumn through early spring while dormant. They need planting promptly, or appropriate short-term storage if conditions are unsuitable. Potted plants can be available at other times, although spring and autumn are often easier for establishing roots than a hot summer spell.
Seed-growing is possible, but plants may vary in quality and maturity takes longer. If your aim is dependable stems for cooking, a named variety from a reputable supplier is sensible. Choose by harvest season, vigour and stalk characteristics, not merely whether the pictured stalks are exceptionally red. Green-stalked rhubarb can also be good to eat.
How to plant a rhubarb crown
Dig a hole wider than the root system so the roots can spread without being bent sharply. Set the crown with its growing buds close to the surface; the RHS advises keeping the crown tip just above soil level. Planting deeply can cause the crown to rot.
Backfill with soil, firm gently around the roots and water in if necessary. Allow roughly 75–90cm between plants, as advised by the RHS; rhubarb forms a substantial clump as it matures. Mark the crown's position if planting while dormant so you won't accidentally dig into it before new growth appears.
Apply compost around, rather than directly over, the crown. Thick, wet mulch piled against the growing point is unhelpful. If autumn weather is very wet, keep an eye on drainage rather than repeatedly watering a dormant plant.
A newly planted crown may send up only a few leaves in its first season. That's normal. Resist the urge to pull those stalks: the foliage is producing energy to establish the plant for future years.
When can you start harvesting?
The Royal Horticultural Society advises taking no stalks in the first growing year after planting. In the second year, harvest only a few. By the third season, a healthy crown should be established enough for a more regular crop.
This waiting period can feel frustrating, particularly when even a young plant makes several attractive stalks. Remember that its large leaves are doing important work. Removing too many leaves forces the plant to rebuild foliage instead of storing resources below ground.
For established crowns, spring and early summer are the main picking seasons. The exact start varies with the cultivar and local temperatures. Stop taking regular harvests by late June or early July, or take only occasional stalks from a vigorous established clump afterwards, so the plant can replenish its roots. The RHS recommends taking no more than about one-third of an established plant's stalks at a time.
How to pick rhubarb without damaging it
Choose a firm stalk of useful length with a well-developed leaf. Grasp it close to its base, pull gently outwards and twist so it separates cleanly from the crown. Avoid hacking through the stalk at ground level, because a remaining stump can rot.
Only pick stalks from a mature, healthy plant. Never strip the clump bare. If a plant has weak growth after drought, disease or a recent division, reduce the harvest and give it time to recover.
Cut the leaf blade off the harvested stalk before taking it into the kitchen. Rhubarb leaves must not be eaten: they contain substances, including high levels of oxalic acid, that make them poisonous. Keep discarded leaves away from children and animals that might chew them. The stalks are the edible part, and are normally cooked before serving.
Stalk colour is a variety characteristic and not a reliable test of sweetness or ripeness. Some delicious varieties have green or speckled stalks. Pull when the stalk is a suitable size for your cultivar and the plant has enough foliage to spare.
Watering and feeding established rhubarb
New plants need water through dry spells until their roots have established. A mature clump in suitable ground is fairly resilient, although a long hot drought can slow its growth. Water thoroughly when the soil has become very dry rather than splashing small amounts on the leaves each day.
In spring, spread a generous mulch of well-rotted garden compost around the plant. The RHS describes a layer around 7cm deep, kept clear of the central crown. It improves soil structure, reduces evaporation and suppresses weeds. This may be enough feeding in reasonably fertile soil.
If a plant has poor growth in genuinely impoverished ground, an appropriate fertiliser may help, but diagnose drainage and root problems before assuming it needs more nitrogen. Applying strong feed around a rotting crown won't solve the problem.
Remove flowering stalks as they appear if you're growing for edible stems. A flowering shoot diverts some of the plant's energy from leaf and root development. You can cut it cleanly close to the base without digging into the crown.
What is forced rhubarb?
Forcing means encouraging a strong dormant crown to produce tender, pale stalks in darkness before the usual outdoor harvest. Traditionally a forcing pot is placed over a mature plant in winter. A tall, light-excluding bucket can sometimes serve a similar purpose if it is secure and allows suitable conditions.
Without light, developing stalks become paler and often more tender. Check periodically so the shoots aren't crushed against the top. Do not force a newly planted crown; it needs its first seasons to establish.
Forcing uses stored energy and puts extra demands on the plant. Once the forced stalks have been picked, remove the cover and let the crown recover. Avoid taking another heavy harvest from it that year, and don't force the same crown repeatedly without adequate recovery time.
How and when to divide old rhubarb
After several years, a large clump can become congested. The centre may weaken while stronger buds develop around the outside. Dividing the crown can restore vigour and give you spare plants.
Work during the dormant season, usually between autumn and early spring, when the ground isn't waterlogged or frozen. Lift the clump carefully and use a sharp spade or sturdy knife to separate healthy sections. Each new section must retain a viable bud and a portion of substantial rootstock.
Replant good outer sections promptly into prepared ground. Discard obviously rotten material rather than distributing disease through the garden. Newly divided plants should be treated much like new crowns: allow them to re-establish before harvesting heavily.
Problems that can affect rhubarb
Soft or rotting crown: Check drainage and planting depth. A crown buried beneath soggy compost may decay.
Thin stalks and small leaves: The plant may be young, congested or short of moisture and nutrition. Consider its age and growing conditions together rather than reaching immediately for fertiliser.
Flower spikes: Remove them for a stalk-producing crop. Occasional flowering is normal, especially with older plants or unsettled conditions.
Brown, dying foliage in autumn: Rhubarb naturally becomes dormant. Allow leaves to fade, then clear spent foliage so the growing points remain exposed to winter chill.
A very small crop in the first year: That's expected. Don't solve it by pulling the few stalks available.
Rhubarb asks for patience up front rather than constant work later. Give it room, plant the crown correctly, protect its early foliage and harvest sensibly. In return, a vigorous clump can become one of the most dependable perennial crops in the garden.
Source
Royal Horticultural Society, How to Grow Rhubarb.