When is a fruit not a fruit? When it’s a vegetable, of course! A vegetable, you say? In botanical terms, rhubarb is indeed a vegetable, as it is the herbaceous stem portion that we cook and eat, as opposed to its actual fruit, which by strict definition is the ‘mature, ripened ovary of a plant, including the contents of the ovary’. Conversely, this means that many things we term vegetables are actually fruits – think the squash-pumpkin family, and nightshades such as tomatoes, capsicums and eggplant. A clump of leafy perennial rhubarb is almost as ubiquitous as a lemon tree in Kiwi gardens. Love it or hate it, this tart-tasting, easy-care crop deserves a place in our backyards as a ‘hungry gap’ place-filler, with crops ripening in October and November when other fruit is scarce. Give rhubarb a go, it may be an acquired taste but it just might grow on you!
Rhubarb: a short family history
Rhubarb has a rather interesting backstory. It is a member of the Polygonaceae, the knotweed or smartweed family, which contains other edibles such as buckwheat (Fagopyrum esculentum and F. tataricum), Vietnamese mint (Persicaria odorata) and sorrel (Rumex acetosa) as well as common weed species including docks and the much-feared Japanese knotweed (Reynoutria japonica). Rhubarb sits within the genus Rheum, with species native to Europe, Asia and environs. It is now widely cultivated commercially in Europe, North America and beyond. Rheum rhabarbarum, one of the forebears of culinary rhubarb, is native to Siberia and China and was originally harvested as a medicinal species, with the root utilised as a laxative and cleansing agent, as well as to relieve fever – records of such use in China date back to 2700 BC. The exact genetic origins of culinary rhubarb (Rheum x hybridium) remain a mystery, as members of the genus hybridise readily, but it is likely a hybrid of the medicinal species R. rhabarbarum, R. rhaponticum and others under cultivation in the 18th century. It was also around this time that cultivation for culinary purposes commenced – rhubarb began to be grown as a crop across England and Scandinavia and the edible stems were utilised. We have Joseph Myatt, English market gardener and godfather of modern rhubarb cultivars to thank for rhubarb’s transition from purgative to ‘pie plant’, as it is commonly known in North America.
Given its Siberian origins, rhubarb was (and still is) particularly well-suited to the cool climate of northern England, giving rise to the ‘Rhubarb Triangle’ – formed as rhubarb cultivation boomed in the north in the early 1900s, designated as the area of West Yorkshire bounded by Leeds, Bradford and Wakefield and covering some 30 square miles at its peak. In modern times, the triangle has shrunk to a nine square mile area, but is still renowned for its production of shed-grown, early forced rhubarb, which since February 2010 has had Protected Designation of Origin (PDO) status, raising it to a level of prestige shared with products such as Champagne and Parmigiano Reggiano cheese. The forcing process itself is fascinating. Plants are field-grown without harvesting for two years and fertilised well with animal manure (in the past this also included ‘night soil’!). The rooted plants are exposed to frost and then moved to heated sheds where they are kept in total darkness. The plants begin to grow in the warmth and stored carbohydrates in the roots are converted to glucose, with the resultant bright pink stalks of rhubarb having a sweet-sour flavour. The leaves of forced rhubarb, not having access to sunlight, are a pale yellow-green in colour and the stems are less fibrous and more tender than outdoor rhubarb. Exposure to light halts growth, so forced rhubarb was traditionally harvested by candlelight. The intensive nature of this method of production exhausts the root system and so the whole plant must be discarded at the end of the growing season.
Suitable climates and growing conditions
Due to its extremely hardy nature, rhubarb is able to be cultivated successfully across all regions of New Zealand. Being a cold climate species, rhubarb even thrives in places like Alaska – rhubarb arrived on Kodiak Island in 1784 with the Russian trader Gregorii Shelikhov. Loving not only the cold, but also the long days under the midnight sun, Alaska now boasts some 67 varieties of rhubarb! Some winter chill is required to initiate growth in the spring. Choose a position that is fairly open, sunny or semi-shaded; if in full sun, the plant may wilt quickly on very hot days and growth can shut down during prolonged periods where temperatures are high. As with most fruit crops, avoid overly heavy soil types and waterlogged conditions, as this will cause rhubarb crowns to rot. Rhubarb prefers acidic soils with a pH of 5.0-6.0.
Rhubarb can be propagated by seed in early spring (caution: variation from the parent plant is likely to occur and plants may take three or so years to establish) or clonally by root division. If you have a friend with a desirable cultivar, ask them nicely and they may be happy to oblige! You can divide mature plants after four to five years of growth, splitting the crowns with a sharp spade or knife when the plant is dormant (autumn or early spring is recommended), ensuring each new piece has at least one growing point (bud). Rhubarb plants can also be purchased from most nurseries and garden outlets.
Dig a trench for your rhubarb crowns, 50-60 cm deep, allowing sufficient space between plants – about 75 cm to one metre is ideal. Dig in plenty of well-rotted manure or mature compost and plant the crown at a depth where it will be covered by no more than five centimetres of soil when the trench is filled in. Rhubarb thrives in raised beds, but if you do not have this luxury, you can take heed of the late Jonathan Spade’s advice and add some gravel, broken crockery or scoria to the bottom of your planting trench to aid drainage.
Let the newly planted crowns grow unchecked in their first year – if growth is satisfactory, you can start light harvests from crown-grown plants in their second spring. Break the stalks (known as ‘sticks’) off by grasping each near the base of the plant, pulling up and out with a twisting motion. Always leave a minimum of four or five leaves at the end of the harvest season to allow the plant to produce reserves for the winter and next season. Full productivity will be reached at the four or five year mark and established clumps will crop for ten years or more if well-maintained. You may find that seed-grown plants require an extra two to three years’ unhindered growth in the establishment phase before you can begin harvesting.
Remove the flower spikes as they appear in spring and summer to maintain vigour, diverting the plant’s energy into stem production. Do not allow your rhubarb plants to dry out in the heat of summer, and in the autumn, mulch the plants well with more manure or compost.
A word of warning: rhubarb leaves are toxic, containing oxalic acid and anthrone glycosides. They should not be consumed by humans or fed to livestock. The edible stems do also contain oxalic acid, and an excess of this in the human diet can lead to kidney and bladder stones. Caution should be exercised around consumption by those prone to such conditions, or digestive disturbances.
Rhubarb leaves can be safely composted and you can also boil them up in water and use the resultant liquid as a natural insecticide spray (apparently it is particularly effective against aphids) or add to planting holes when you put in your next crop of brassicas, as it is said to have activity against the fungal pathogen which causes club root.
Pests, diseases and what to do about them
Rhubarb is affected by very few pests and diseases in New Zealand. In warmer climates, armyworms may cause chewing damage but can be brought in check with a pyrethrum spray (prepare according to label directions and observe the withholding period (the amount of time which must elapse between spraying and subsequent harvesting).
If you notice irregular-shape brown spots on your rhubarb leaves, you may have a case of rhubarb leaf spot, caused by the fungus Ramularia rhei. To remedy this, cut off and burn the infected leaves (do not compost). Apply a foliar feed fortnightly (this can be seaweed, fish or comfrey-based) until the symptoms disappear. Make sure the plants are not waterlogged and remove dead or dying leaves and stems to make sure there is good airflow through the canopy.
Varieties: My top picks
Rhubarb varieties can be divided into three types: early, main crop and ever-bearing varieties. If you are a rhubarb aficionado, you could plant some of each type and ensure you can harvest rhubarb continually from early winter right through until midsummer.
Ever-bearing types are harvested in the winter period, when they are most vigorous, then are best left to build up their reserves for the rest of the growing season.
Early and main crop varieties will usually be dormant in winter and hit peak growth (and their harvest window) in spring and early summer, they then need to be left alone to build reserves in mid-to-late summer.
Here are a selection of cultivars that have been, or are currently available for purchase in New Zealand. Chances are, if you are procuring crowns from a friend, you will end up with an unknown or un-named variety, but as long as it suits your needs, no worries!
Topp’s Winter (Australia, 1890) – ever-bearing, parent of Luther Burbank’s Crimson Winter (1900). Early (Prince) Albert (UK, 1840) – early, scarlet stems, robust flavour. Glaskin’s Perpetual (UK, 1920s) – early, can be cut in first year, lower in acid, tender greenish stems. Hogan’s Shillelagh (I’m guessing Ireland – mentioned for sale in the New Zealand Tablet of 3 January 1901 along with Giant Victoria) – early, large plant, thick pink-green stems. (Giant or Myatt’s) Victoria (UK, 1837) – main crop, large green stems.
Modern or improved selections currently available through seed companies, Incredible Edibles or Mitre 10: Moulin Rouge Winter’s Wonder Crimson Crumble Ruby Tart/Ruby Red
What to do with your crop
It’s late spring and you are overrun with crimson stalks of rhubarb, what to do, what to do? After you’ve exhausted all the usual avenues such as rhubarb crumble and rhubarb pie, you can move on to rhubarb sago, and if you slice and free-flow freeze a few bags, you can add rhubarb to your early summer berry jams (think strawberry, raspberry and blackcurrant) to improve the set and texture. If you have a nice bright red variety and make elderflower cordial, try adding a couple of cups of thinly sliced raw rhubarb to the brew along with the elderflower heads for a pink hue and subtle tangy rhubarb note – the resultant mix is a true spring elixir. Rhubarb is a popular choice of base fruit among home or ‘country’ winemakers. I also like to make fruit leathers from a blended mixture of 50% stewed apple, 25% strawberries (raw or lightly cooked) and 25% stewed rhubarb.
I’ve always been intrigued by those die-hard rhubarb fans who have childhood memories of sitting in the garden chomping on a raw stalk dipped in sugar. I’m not game enough to try this myself but I have tried a slice raw while preparing fruit for cooking – not something I’m that excited about repeating. In French cuisine, rhubarb-based sauces are made to accompany fish dishes. I was also interested to read that the unopened flower heads are cooked as a seasonal vegetable delicacy in Asian cuisine, often cultivated specifically for this purpose. It is the flower heads themselves that are prepared, a little like broccoli or cauliflower florets – first, you need to trim away the stem, the papery bract that covers the flowers and any small leaves arising from this part of the stem. The flower clusters are then broken into little chunks, and can be prepared by steaming, stir-frying or boiling, much as you would the heading brassicas. The slightly sour flavour apparently does away with the need for lemon juice or vinegar as an accompaniment, a little oil and salt are sufficient to dress the cooked florets. As with rhubarb stems, oxalic acid is present, so consume in moderation. I plan to give this a go as I have some flower stalks currently forming in my rhubarb patch.
Rhubarb has a few interesting non-culinary applications. I’m a keen amateur soapmaker – the roots of Himalayan rhubarb (R. australe) yield strong pink to red hues when the dried root is infused in a base oil and used to make soap. When you next burn food to the bottom of your favourite saucepan, use rhubarb juice to help remove the mess – thanks to the oxalic acid, this also works for cleaning tarnished metal. If you’ve ever eaten old stringy rhubarb, you’ll appreciate that rhubarb stem fibre has been used to make paper in the past.
Hopefully you get a chance to try some of these alternative uses, and don’t forget to slice and freeze a few bags of fruit for out-of-season-use.
Rhubarb & Custard Muffins Makes 12 standard muffins
Fruit mix: 260 g/2 cups fresh rhubarb, cut into 1 cm dice 2 tbsp sugar
Muffin mix: 1 ¾ cups plain flour and 4 tsp baking powder OR 1 ¾ cups self-raising flour ¼ cup custard powder ½ teaspoon salt ½ cup caster sugar
Wet ingredients: Approximately 1 cup milk 100 g butter, melted 1 egg
Approximately ½ cup readymade custard
Crumble topping: ½ cup plain flour 50 g butter, diced ¼ cup soft brown sugar ½ teaspoon ground cinnamon
Preheat oven to 200°C and line a 12-hole muffin pan with paper cases.
Line a 20 x 20 cm brownie pan or Pyrex dish with baking paper, place the diced rhubarb and sugar on the paper and mix with your hands until the fruit is coated in sugar. Bake for 10 minutes, stir gently, then cook for a further five minutes, until the fruit begins to soften but not lose its shape. Remove from the oven and tip into a sieve set over a bowl to catch the juice. Set aside to cool while you prepare the other ingredients.
Place the dry muffin mix ingredients in a large mixing bowl and whisk together to combine.
In another (small) bowl, combine all the crumble topping ingredients, rubbing in the butter until the mixture resembles sandy, clumpy breadcrumbs.
Pour the drained rhubarb syrup into a measuring cup or jug, and make the volume up to 1 cup (250 ml) with milk.
Melt the butter in a small saucepan, cool slightly. Beat in the eggs and milk/juice mixture.
Add the wet mixture to the dry ingredients, stir gently, then add the drained, cooked rhubarb. Mix gently to combine, do not overmix or the muffins will be tough and peaky. A few patches of flour remaining throughout the mix are fine.
Place a large spoonful of batter in the base of each muffin case. Top each with a teaspoon of prepared custard. Follow this with another spoonful of muffin batter.
Sprinkle a good teaspoonful of crumble topping over each muffin. If you have some of this left over, place in a small container or snaplock bag and freeze for your next baking day.
Bake for 20-25 minutes, until well risen and brown. Cool before serving.
For dairy free muffins, substitute Olivani or a similar spread for the butter, plant-based milk such as oat or soy for the milk, and a dairy-free custard (Alpro is excellent) for the readymade custard.
Anna-Marie Barnes is an active member of the New Zealand Tree Crops Association who endeavours to grow and preserve as much of her own fresh produce as possible. When the weather’s no good for gardening, she can usually be found inside working on a batch of homemade cheese or soap.
The New Zealand Tree Crops Association is a voluntary organisation promoting interest in useful trees, such as those producing fruit, nuts, timber, fuel, wood, stock fodder, bee forage and other productive crops. Find out more about the NZTCA here: https://treecrops.org.nz/
Di Reynolds – Pixabay https://pixabay.com/photos/rhubarb-plant-garden-rhubarb-1406455/ Alex Fox – Pixabay https://pixabay.com/photos/rhubarb-fruit-spring-nature-leaves-5155214/