Rhubarb is a rhizomatous perennial whose stems (‘sticks’) grown as vegetable but used mainly as a dessert. It crops over a long period, is completly hardy and grows in any garden soil.
Any fertile garden soil can be used for rhubarb as long as it is well drained and in full sun. Crowns (‘sets’) can be cropped for ten or more years, though division may be necessary after about five years.
Preparing the soil
Although the large foliage can help smother weeds, the ground should be free from perennial weeds before planting. Dig in one to two bucketfuls of well-rotted organic matter such as manure, before planting.
Plant crowns in November or December. If necessary, planting can continue up to the beginning of March. Buy named cultivars or choose a division from a strong, healthy-looking plant.
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.
In hot summers, if the ground becomes dry, growth will slow down and even stop. A spring mulch of well rotted organic matter 7cm (2 1/2in) deep will help to retain moisture but do not bury the crowns. Plants will also respond to watering during prolonged dry periods in summer. Apply a general fertiliser such as growmore in spring or summer at 70g per sq m (2oz per square yard).
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 acid contained in them breaks down during decomposition.
Stems can be picked from the early cultivars from March to April. Do not harvest in the first season after planting and harvest only lightly in the second season to avoid weakening the crowns. From seedling plants, harvest in the second season after planting or in the first season after division.
Stems should be pulled rather than cut to prevent rotting of the remaining stump. Pull stems when they are between 23-30cm (9-12in) long, holding them at the base and pulling gently outwards. Take no more than half the total stems at any one 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 acid 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.
For an early harvest of tender and pink rhubarb cover the crowns in December or January with a layer of straw or 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 earlier than uncovered crowns.
For an even earlier harvest, lift some roots in November. Ideally leave the lifted roots outside for up to two weeks prior to potting to expose them to more cold - this is needed to overcome dormancy. Then pot up with compost and bring into a cool room or greenhouse at a temperature of between 7-16ºC (45-60ºF). Exclude light with buckets or black polythene over crates. 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.
Sow seed in spring (March/April) 2.5cm (1in) deep in a seedbed or individually in modules. If in a seedbed thin seedlings to 15cm (6in) apart, choosing the most vigorous seedlings. The resulting plants will be more variable than named clones. Plant out in autumn or the following spring.
Division will guarantee a plant identical to the parent and is the most common method of propagation. It is also good practice to divide established crowns about once every five years if they have become weak or overcrowded. Lift crowns between autumn and early spring (usually in November).
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.
‘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.
‘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.
‘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.
‘Victoria’ – Late, cardinal red stems with flecking at top. Red flesh tinged green. Very thick stems. Popular old variety.
Flowering: Some cultivars can be more prone than others. Remove flower stalks as soon as they appear to prevent them weakening the crowns. Flowering is usually worse after wet summers or where high nitrogen feed has been overused.
Thin, weak stems: Lots of thin stems indicate the crown is losing vigour and needs to be divided (see ‘Propagation’). Increased feeding may also help.
Split stems, sometimes exuding sticky sap: This is sometimes caused by late frosts but is often an indication of erratic growth due to seasonal conditions. Cool or dry periods followed by moist or mild weather means the hard outer growth splits when the new, rapid growth occurs. Mulching and feeding may help to avoid the worst damage.
Green, poor quality stems: Warm, dry summers can give rise to poorly-coloured, bad-tasting stalks. Try to harvest earlier while the days are cooler and moister.
Slow or no growth: Rhubarb will stop growing if the temperature rises above 32ºC (90ºF). This can happen in hot summers. Growth can also slow or stop if the plants are under drought stress so watering may help.