Rhubarb (Rheum x hybridum) is a rhizomatous perennial whose stems ('sticks') are harvested for culinary use, usually as a dessert. It has a long period of cropping and most cultivars are suitable for forcing. Expected yield is .-5. 13.5kg per 3m (10-30lb per 10ft) row. Crowns ('sets') can be cropped for ten or more years, though division may be necessary after five or so years. Rhubarb has a cold requirement of between seven to nine weeks below 3°e (37°F) depending on the cultivar to bring it out of winter dormancy and is commercially grown mostly in the north of England.
Site and soil
Preparation of the soil
Plant the crown with the growing point at, or just below, the soil surface. On wetter soils planting with the buds just raised out of the soil may help prevent rotting.
If planting more than one crown, space plants 1m (3ft) apart, with 1-2m (3-6ft) between rows.
Allow the foliage to die back naturally in autumn, then cut away the old leaves to expose the growing points to winter cold. There is no harm in adding these . leaves to the compost heap as the poisonous ·oxalic add contained in them breaks down during decomposition. Compost made from them makes a good soil conditioner.
Use a spade to divide the crown into sections, each retaining a portion of the rhizome_ (thickened root) and at least one growing point. Sections from the outer part are better than the centres of old plants. Discard any old or decayed parts of the crown. Replant straight away or wrap in damp sacking until ready to plant.
By Tissue Culture
Stems should be pulled rather than cut to prevent rotting of the remaining stump. Pull stems when they are between 23-30cm (9912in) long, holding them at the base and pulling gently outwards. Take no more than half the total stems at anyone time.
The last harvest is usually in late summer, around July or August, though growth may have stopped before this if the weather is very hot. Concern is sometimes expressed over the concentrations of oxalic add building up as the season progresses. However, this build-Up is mostly in the leaves which are not eaten and the amount in the stems is not sufficient to have a toxic effect.
Forcing results in earlier stems which are more tender and pinker than. unforced rhubarb. Cover the crowns in December or January With a layer of straw at bracken and cover over with an upturned bucket or a traditional clay rhubarb pot to exclude light. Stems will be ready to pull two to three weeks later.
For an even earlier harvest, lift some roots in November. If there has been insufficient cold it is possible to leave the lifted roots outside for up to two weeks prior to potting to expose them to more cold. Then pot up with compost and bring into a cool. room or greenhouse at a temperature of between 7-16°C (45-60°F). Exlude light with buckets or black polythene over crates. Alternatively, pack the roots into a large black bin and replace the lid, uncovering at night to provide ventilation. Keep the roots damp but not wet. Stems can usually be harvested in five weeks. Crowns forced in this manner are usually much weakened and therefore discarded after harvest.
Thin, weak stems
Split stems, sometimes exuding sticky sap This is sometimes caused by lat~ frosts but is often an indication of erratic growth due to seasonal conditions. Cool or dry periods followed by moist or mild-weather means that the hard outer growth splits when the new rapid growth occurs. Mulching and feeding may help to avoid the worst damage.
Green, poor quality
Slow or no growth
Dieback of crowns
'Early Champagne' - even cardinal red colour throughout length of stem. Green flesh, pink at edges. Good, strong, reliable cultivar.
'Early Cherry' ..:. bright reddish-pink base with red flecking on green towards top. Flesh green. Thick stems.
'Goliath' - very dark red base of stem paling to green at the top. Good, strong weed suppressing cultivar. Good rating in Harlow Carr taste tests.
'Grandad's Favorite' - currant red stems with some flecking and green streaking at top. Green flesh. Heavy cropper.
'Hawke's Champagne' - even currant red colour throughout length of stem. Flesh pale green through to pink. Leaves heart-shaped and attractive. Vigorous. Reliable early variety.
'Reeds Early Superb' - a good red stem along most of the length. Leaves glossy dark green. Good for forcing.
'Stein's Champagne' - very attractive, slender, deep red stems. Dark red flesh throughout.
'Stockbridge Arrow' - cardinal red stems with some lighter streaking and flecking. Flesh pink with white background. Thick stems. Small, triangular, red-veined leaves .
Good for forcing, producing. - deep red, straight sticks. Heavy cropper.
'TImperley Early' - base deep red, passing to light green with red flecking. Does not hold colour well. Green flesh with reddish tinges. Heavy cropper. Good for forcing. Disappointing in Harlow Carr taste tests. Frost susceptible.
'Cawood Delight' (mid- to late season) (good deep red stems of high quality. Poor cropper.
'German Wine' - deep pinkish-red stems with some flecking at top. Red flesh. One of the best for colour.
'Strawberry' - vermilion base deepening to currant red at top. Pink-tinged flesh with white middle. Very attractive colouration. Good rating in Harlow Carr taste tests.
'The Sutton' - currant red base of stem becoming green with red flecking. Green flesh with some red tinges. Thick stems. Good for forcing.
'Zwolle Seedling' - greenish-pink young sfems maturing to carmine red. Light green flesh. Good rating in Harlow Carr taste tests.
'Victoria' - cardinal red stems with flecking at top. Red flesh tinged green. Very thick stems. Popular old variety.