Polygonaceae, the knotweed family.
Rhubarb is a cool season, herbaceous perennial related to wild dock and sorrel. A decorative leafy plant with thick red, pink or green stalks, depending on the variety, it can reach a meter in height, and is a useful addition to the general garden landscape, thus freeing up valuable space in the vegie patch! It requires a cold winter, with the best stem colour produced at approximately 10˚C, and can be difficult to grow in areas with very hot summers or high humidity. A tough plant which, once established, can cope with a fair amount of neglect and minimal water, and can be successfully grown in the ground or a pot.
Rhubarb is gown in the open in Australia and is available all year, unlike in Britain and Europe where it is often forced out of season (see note on forcing). During the winter months in Australia it grows more slowly, resulting in thinner, redder stalks, while in the warmer weather the stalks grow thicker and tend to be more of a greenish red.
Rhubarb can be grown from crowns or seed, and three or four plants should be enough for most people. Once established, leave the plant undisturbed for 4-5 years before digging and dividing it. The plants do send up large flower spikes in the colder months, it is advised that these be removed to promote stronger plant growth.
While rhubarb is actually a vegetable, when it comes to culinary use, it is generally treated as a fruit and has even been referred to as the “pie plant” giving you an indication of what it may be used for in the kitchen.
Climate: Rhubarb is a cool season crop requiring temperatures below 5 °C/40 °F to break dormancy and stimulate spring growth and warm summers to encourage vigorous vegetative growth.
Healthy rhubarb ready for picking
Companions: Strawberries, also brassicas, garlic and onion.
Dormancy: Rhubarb needs a cold period to break the winter dormancy and start new growth, but it is important not to plant it in a frost pocket.
Feeding: At the beginning of spring mulch your rhubarb with well rotted manure and compost, but do not allow the mulch to come in contact with the crowns.
Forcing: In the colder climes hibernating plants are tricked into early arrival by forcing them with covers This can be done in the bed where it is planted or by moving the plant indoors.
In situ – In early winter, before rhubarb can be forced, it needs to experience a certain amount of cold weather. Tidy all dead foliage and debris from the top of the crowns thus exposing them to as much frost as possible prior to preparing them for forcing. Then in mid winter place dry material such as leaves or straw around the plant and then position a deep container over the plant to exclude light for about a month.
Indoors – Alternatively, in mid autumn healthy rhubarb crowns are lifted and left on the soil surface for 7-10 days to expose them to frost. The plants are then put in pots of compost and left in a shed, cellar or garage with a constant termperature of 15-17C (any warmer and they’ll rot). The soil is kept just moist, and all light excluded from the rhubarb. Good ventilation is required at night to deter rotting.
In both cases make regular inspections of the plants to ensure they are not rotting. Start picking rhubarb stems as soon as they are large enough.
Frost tolerant: Yes, to a degree. We have found that long spells of severe frost can be quite damaging to the stalks, and if we have severe frost warnings, we now cover the plants with large upturned pots overnight.
Rhubarb after a series of very heavy frosts…
Harvesting: In cool areas pick stems by hand from spring until early summer. Where winter temperatures are mild, rhubarb can be harvested almost year round. Harvest as soon as the leaves are fully open by grasping the base of the stalk and pulling it away from the pant with a gentle twist. This generally removes the entire stalk. Always leave at least four stalks per plant to ensure continued plant growth. (Be sure to discard the leaves because they contain high amounts of oxalic acid and are considered toxic.)
Do not harvest during the first year of growth to ensure the plant has time to become established.
Height: Up to 1 meter
Position: Sun or partial shade, but best in full sun. (Do not plant in a frost pocket.)
Problems: Rhubarb can be prone to bacterial crown rot. This causes the young leaves to shrivel and eventually kills the plant. Plants should be dug up and destroyed. Snails and slugs can damage the stems, although I have not had any issues here.
Propagation: Can be grown from seed or crowns.
Seeds – Sow seeds in early spring into a prepared seedbed or pots, note that seeds require temperatures of 20 – 23 ˚C for germination. Your seedlings should be ready to be planted out in the following autumn. It should be noted that seedlings take a few years to reach maturity.
Crowns – Crowns are divided sections of mature plants. I think that this is the easiest way to grow rhubarb. You can purchase crowns from a nursery, or if you know someone who has rhubarb growing in their garden, they may be willing to divide their plants and give you a piece). Crowns should be planted any time during winter and early spring. Prepare the rhubarb bed with well rotted manure and compost, keeping in mind, that this is where the rhubarb will remain. Plant the crowns with the dormant buds just above the soil.
Dig and divide clumps every five or six years.
Soil: Before establishing a new bed, dig in plenty of compost and well rotted manure – the soil needs to be well-drained, but moisture retentive. Avoid heavy soil, as it can rot the crown.
Sow and plant: Rhubarb can be planted from crowns in winter, or seedlings in autumn. Pot-grown rhubarb plants can be bought and planted in early spring. Plant so that the crown (where the new shoots emerge from) is just at ground level.
The large ornamental leaves of the rhubarb plant makes it an attractive feature in the flower garden garden.
Spacing: Space the crowns 75-90 cm apart in well prepared, free draining soil.
Storage: Rhubarb becomes limp quite quickly after picking. Slice off and discard the leaves, wrap in plastic wrap or place in a plastic bag and store in the vegetable compartment of your refrigerator for up to a week.
Cooked rhubarb can be store in a covered container in the refrigerator for 4-5 days, or it can be frozen. Rhubarb can also be preserved for pies and compotes, and it can be made into jams, relishes and sauces as well.
Watering: Keep well watered for the first growing season, and the then just water well during dry spells.
Note: Rhubarb leaves and roots are poisonous, they contain oxalic acid, so you should never eat these portions of the plant. They should never be fed to livestock or poultry either.
Uses in the Kitchen
Only the rhubarb stalks should be eaten and they must be cooked. Rhubarb is rich in iron, and vitamins A and C and is generally used as a fruit in compotes, purees, pies and
crumbles all of which are wonderful paired with custard, cream, ice cream or natural yoghurt. It combines beautifully with strawberries, apples and ginger in dessert recipes, and the tartness of the rhubarb also makes it an ideal base for sauces, relishes and jellies to be paired with rich meats. I also like to use it when making cakes as well.
Rhubarb has a high moisture content so it barely needs any more added when cooking. When preparing rhubarb stalks for cooking, remove all leaves, and cut off the flat brown part from the bottom of each stalk and discard. Wash the stalks and if the stalks are very large, peel to remove the stringy exterior. Your recipe will generally tell you what lengths to cut the rhubarb to.
Uses in the Garden
The oxalic acid in rhubarb leaves makes it a useful ingredient in a natural spray to kill insects such as aphids, pear and cherry slug whitefly and caterpillars.
Note that rhubarb leaves are poisonous to humans and animals, therefore appropriate safety guidelines should be followed when preparing and using rhubarb leave insecticide spray.
- Wear gloves and goggles during preparation and use of the spray
- Wear long sleeved shirt, trousers and waterproof footwear.
- During preparation if boiling the plants, wear a mask, don’t inhale the fumes, and work in a well ventilated area.
- Do not use equipment that will be used for food preparation and do not work near food.
- Stainless steel and enamel saucepans whould be used for boiling and you should use glass or enamel bowls for infusions.
- Always store in glass jars with secure lids and ensure that the jars are clearly labled.
- Wash all equipment, hands and clothes after use.
- Do not spray on very hot, windy or wet days.
- Do not consume sprayed food within within 48 hours after spraying.
- Pest-repellent Plants, P Woodward, 2011, Hyland house publishing
- Harvest, S Bittner & A Harampolis, 2017, Ten Speed Press
- Grow your own Kitchen Garden Year, M Beazley & The Royal Horticultural Society, 2009, Octopus Publishing.
- Dig – Modern Australian Gardening, M Kirton (2003) Murdoch Books Australia.
- The Cook’s Companion, S. Alexander (1996) Penguin Book Auatralia.