It is often assumed that rhubarb needs little attention. However, poorly nourished clumps and hot, dry summers slow down growth and the weakened stems are liable to produce a poor and bitter tasting crop.
Rhubarb benefits from a generous mulch with organic matter in spring. Garden compost, composted bark and well-rotted farmyard manure are all suitable. Try to mulch around the crowns rather than burying them. This will help reduce drought stress during summer and ensure a longer picking season. In late February or early March apply a dressing of sulphate of ammonia at 70g per sq m (2oz per square yard). Don’t overdo feeding with nitrogen as this can lead to undesirable flowering.
However, thin, weak stems may also indicate that the crowns have become overcrowded and need dividing. Divide crowns every five or six years. Lift them when dormant, usually by November, using a fork to avoid damaging the thick roots.
Then, using a spade, split the crown into sections with a healthy portion of thick root and at least one strong bud; discard old or decayed material. Replant or wrap in damp sacking until ready to plant.
You can divide rhubarb anytime from November until early March. Cultivate the soil deeply, adding plenty of well-rotted farmyard manure. Drainage is important and as the crop will be there for a number of years, eradicate all perennial weeds prior to planting. Plant the crown with the growing point at, or just below, the soil surface. On wetter soils plant the bud just above the soil to prevent rotting. Space plants 1m (3ft) apart, with 1-1.8m (3-6ft) between rows.
For an early harvest, try forcing. This will produce stalks in as little as five weeks. Lift whole crowns in November and place on the soil surface to be chilled, preferably frozen solid, for two weeks prior to potting up. This exposure to cold promotes growth by breaking dormancy early. Then, either replant in situ or pot up with compost and bring into a cool room or greenhouse (7-16ºC/45-60ºF). Totally exclude light using pre-moulded forcing pots, buckets or black polythene arranged over plastic crates. For outdoor crowns stack rotting organic matter over the covers to insulate the crowns. Alternatively, place the roots into a large black bin and replace the lid. Keep damp and uncover at night to provide ventilation. Forced crowns in the ground will need a season to recover whereas crowns in pots, are best discarded after harvest.
If you are tempted to plant some new crowns then the best time for this is autumn or late winter. ‘Canada Red’ has very deep red stems with the colour consistent right through the stem. ‘Appleton’s Forcing’ is, as might be expected from the name, a cultivar suitable for forcing and has good flavour. The flesh is pale green with a red tinge. For a long season of pulling, plant ‘Baker’s All Season’ which has red-centred flesh. For suppliers see the RHS Plant Finder, available free online or in book form from bookshops or RHSE, tel. 01483 211113.
Fiona Dennis