Rhubarb is grown primarily for its fleshy stalks, technically known as petioles. The use of rhubarb stems as food is a relatively recent innovation, first recorded in 17th century England, after affordable sugar became available to common people, and reaching a peak between the 20th century's two world wars. Sometimes thought as a fruit it is indeed a vegetable
Commonly, it is stewed with sugar or used in pies and desserts, but it can also be put into savoury dishes or pickled. Rhubarb can be dehydrated and infused with fruit juice. In most cases, it is infused with strawberry juice to mimic the popular strawberry rhubarb pie.
Rhubarb root produces a rich brown dye similar to walnut husks. It is used in northern regions where walnut trees do not survive.
Benefits of the Rhubarb
- Useful source of potassium
- Rhubarb leaves contain poisonous substances, including oxalic acid which is a nephrotoxic and corrosive acid that is present in many plants.
- May aggravate joint problems in those that suffer with arthritis or gout.
- For cooking, the stalks are often cut into 1 inch (2.5 cm) pieces and stewed (boil in water); it is necessary only to barely cover the stalks with water because rhubarb stalks contain a great deal of water on their own.
- 1/2 to 3/4 cup of sugar is added for each pound of rhubarb
- Spices such as cinnamon and/or nutmeg can be added to taste.
- Sometimes a tablespoon of lime juice or lemon juice is added. The sliced stalks are boiled until soft. An alternative method is to simmer slowly without adding water, letting the rhubarb cook in its own juice.
- Roasting with a couple of tablespoons of water and a good sprinkling of sugar over the top is another great method.
When to sow
- Indoors in March or April at a minimum of 15˚C
- Outdoors when tempertures rise above 15˚C and no chance of frost so from mid May till July
How to sow and plant Rhubarb
- 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.
- Can be grow from seeds or by dividing existing crowns.
- Seed should be sown indoors in February and plant out in May.
- New sets should be planted in its dormant phase between October and March unless the ground is frozen..
Planting Rhubarb from Crowns
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.
- 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.
- Sow seed in February/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.
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.
Great Rhubarb to try:
Glaskins Perpetual Rhubarb
- Quick growing, producing bright red sticks with fine flavour over a long period.
Stockbridge Arrow Rhubarb
- The forcing variety that will perform well outdoors and crop over a long period.
- Upright red sticks.
Timperley Rhubarb Early
- The earliest variety into production with red sticks at the base turning green higher up.
- Good for forcing.
- The traditional variety, first introduced in 1837.
- Excellent flavour and high yielding.
Problems Growing Rhubarb
- 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.