Rhubarb

Start from seed: Not recommended (use crowns instead)

Optimum soil temperature for germination: Not applicable

Plant crowns: March-May or August-September

Plant spacing: 80-90 cm

Days to maturity: 12-18 months (no harvest first year)

Introduction

Rhubarb (Rheum rhabarbarum) belongs to the Polygonaceae family and is a hardy perennial vegetable grown for its thick, succulent leaf stalks (petioles) that are used in cooking. Despite being used primarily in sweet dishes like pies and desserts, rhubarb is botanically classified as a vegetable.

Rhubarb has an ancient history, having been cultivated in China for over 5,000 years, primarily for medicinal purposes. It wasn’t until the 17th century that rhubarb began to be used for culinary purposes in Europe, and by the 18th century, it was being grown commercially in Britain. Early European settlers brought rhubarb to Australia, where it has since become a staple in many home gardens.

The rhubarb plant forms a rosette of large, decorative leaves on thick, coloured stalks that emerge from a crown of rhizomes. The stalks can vary in colour from green to pink to deep red, depending on the variety. It’s important to note that while the stalks are edible, the leaves contain high levels of oxalic acid and are toxic when consumed.

Rhubarb is particularly well-suited to Canberra’s climate with its cold winters and warm summers. It thrives in areas that experience winter frosts, which help stimulate growth in spring. With proper care, a rhubarb plant can remain productive for 5-15 years or even longer, making it a valuable addition to any perennial food garden.

Site and soil

Rhubarb grows best in Canberra when planted in a sunny position, with at least half a day of full sun and from protection against hot afternoon summer sun, which can stress the plants and affect production.

Good drainage is essential for rhubarb, as it doesn’t tolerate wet feet. Rhubarb prefers a soil pH of 5.5-6.5. It is a heavy feeder and will perform best in rich, fertile soil. A raised bed is ideal for ensuring good drainage, in areas with heavy clay soil. Prepare the soil thoroughly before planting by incorporating plenty of organic matter such as well-rotted cow manure and compost. If your soil is heavy clay, consider adding gypsum to improve drainage and prevent crown rot, which can be problematic in poorly-drained soils.

Rhubarb can also be grown successfully in large containers (at least 50-60 cm in diameter and depth), but remember that container-grown plants require more frequent watering and feeding than those planted in the ground.

For details on preparing soil and pots, including the use of lime, dolomite, gypsum and fertilizers, please refer to the COGS guide to garden bed preparation.

Planting Seeds and Seedlings

Rhubarb is not typically grown from seed for home gardens, as seed-grown plants are not true to type and take up to 3 years to reach harvestable size. Instead, obtain crowns (divided parts of an established plant) or potted plants from reputable nurseries or fellow growers. Green stalked rhubarb is due to the variety and will not suddenly turn red so if you don’t like green rhubarb make sure you obtain crowns with red stalks. 

In Canberra, the best time to plant rhubarb crowns is in autumn (March to May) or late winter to early spring (August to September). This timing allows the plants to establish before the extreme temperatures of summer or winter.

When planting, dig a hole slightly larger than the crown and place the crown so that the growing buds are just at or slightly above the soil surface. Planting too deep can cause rotting. Space plants 50-90 cm apart to allow for their mature spread. After planting, water in well with a seaweed solution to help reduce transplant shock.

Apply a 5-7 cm layer of organic mulch such as pea straw, lucerne, or sugar cane around (but not touching) the crown to conserve moisture and suppress weeds. Keep the crown itself free of mulch to prevent rot.

For the first year after planting, focus on establishing a strong root system rather than harvesting. Remove any flower stalks that appear, as flowering diverts energy away from crown development.

Cultivation

Rhubarb requires consistent care throughout the year to maintain healthy growth and sustain regular harvests. It is relatively low-maintenance once established but benefits from regular attention to watering, feeding, and general care.

Water regularly and deeply during the growing season, especially when hot and/or windy. Rhubarb has a deep root system but can suffer during extended dry periods. Consistent moisture is particularly important during spring and early summer when the plants are actively growing. Reduce watering in winter when the plants are dormant.

At least once a year rejuvenate the soil by adding compost and or aged manure and complete organic fertiliser. This is best done in late winter before new growth begins and again after harvesting ends in autumn. Rhubarb is a heavy feeder and appreciates regular applications of nutrients. 

Remove flower stalks as soon as they appear, as flowering diverts energy from leaf, stem and root production and can weaken the plant. In late autumn, tidy up any dead or dying leaves to prevent pest and disease buildup.

Rhubarb will naturally become dormant during Canberra’s winter months, with the foliage dying back before resurging in spring. This winter chill period is essential for good production in the following season. 

To maintain productivity, divide crowns every 3-5 years. This is best done in late winter when the plant is dormant. Lift the crown carefully, divide it into sections ensuring each has at least 2-3 buds and strong roots, and replant in freshly prepared soil.

Harvesting

The key rule for rhubarb is to avoid harvesting during the first year after planting. This allows the plant to establish a strong root system that will support healthy growth and abundant harvests in future years.

In the second year, harvest lightly, taking only a few stalks per plant and leaving most to continue strengthening the plant. From the third year onward, you can harvest more extensively, but always leave at least 4-5 stalks on the plant to keep it growing vigorously. Always harvest the stalks with fully expanded leaves.

Harvest rhubarb by grasping individual stalks near the base and pulling them sideways and downward with a gentle twisting motion. This method ensures the whole stalk comes away cleanly without leaving a stub that could rot. Avoid cutting stems, as this can introduce disease.

Always remove the leaves before bringing the stalks indoors, as the leaves contain toxic oxalic acid and should never be eaten. The leaves can be safely composted and do not pose a risk to chickens.

The main harvesting period in Canberra is from late spring through summer and early autumn. Some varieties, particularly those with red stems, produce better in cooler weather and may slow down during the hottest months. If the harvesting period is too long, or it is picked continually, subsequent yields will be lower because the plant is constantly using reserves to put on new growth. Therefore, after 3-4 months of harvesting, allow the plant to grow freely for the remainder of the season to build up energy reserves for the following year.

Problems

The best approach is to have a reliable Australian reference book to identify problems. Garden Pests, Disease and Good Bugs by Denis Crawford is recommended.

A general strategy to follow with any problem is to observe the plant carefully before taking action. Identify the problem then carefully consider the course of action. For example, with pest insects, you often can see a predator nearby. If you watch and wait the predator may deal with the problem for you. Beneficial predatory insects which feed on pest insects can be purchased from suppliers such as Bugs for Bugs. If the problem needs further action the above recommended book has suggestions. 

Practicing good garden hygiene, crop rotation, and maintaining plant vigour by providing adequate nutrients are key strategies for prevention.

While rhubarb is generally robust in Canberra’s climate, it can encounter a few problems:

Crown Rot: This fungal disease causes the crown and roots to rot, leading to plant collapse. Symptoms include yellowing leaves and wilting despite adequate water. Prevention is the best approach—ensure good drainage, avoid overwatering, and keep mulch away from the crown. There is no cure once established; affected plants should be removed and destroyed.

Leaf Spot Diseases: Various fungal pathogens can cause spots on rhubarb leaves. While unsightly, these rarely affect the edible stalks significantly. Improve air circulation, avoid overhead watering, and remove affected leaves promptly. In severe cases, copper-based fungicides may be used.

Slugs and Snails: These pests may damage young growth, particularly in spring. Control with beer traps, copper tape, or commercial organic baits (iron EDTA). Collect snails and slugs at night from known habitats, for example, around garden edging.

Drought Stress: Prolonged dry periods can cause stalks to become thin and stringy. Regular deep watering is essential, particularly during Canberra’s hot summers.

Bolting (Flowering): While not a disease, premature flowering diverts energy from the plant. Remove flower stalks as soon as they appear. Frequent bolting may indicate stress or that the plant needs dividing.

Recommended Varieties

Sydney Crimson: An Australian variety developed for market gardens, it produces long, crimson-coloured stems with excellent flavour. It performs particularly well in winter and is a reliable producer in the Canberra region.

Victoria: A traditional variety with thick stems that are green to pink in colour. It’s renowned for reliability and productivity, with good cold tolerance making it suitable for Canberra’s winters.

Ever Red: As the name suggests, this variety maintains its red coloration throughout the year. It has a sweet flavour and performs well in Canberra’s climate with its good cold tolerance.

Cherry Red: is a much-prized old South Australian variety grown in the trade for perhaps 60 years as the preferred year-round cropper in the Adelaide Hills. A distinctive blueberry tone to the upright stems to 60cm to 70cm.

Ruby Red: A very old variety from the famous west Yorkshire growing rhubarb area. ‘Ruby Red’ more than likely dates back from prior to 1850 when many new varieties were bred by English growers. It has been kept going in Australia by the Clayton family who have been growing rhubarb commercially in Victoria for the past 120 years or so. 

References

1. Bubel, Nancy. The New Seed-Starters Handbook. Rodale Books, 2018.
2. Crawford D. Garden Pests, Disease and Good Bugs. Australia: ABC Books; 2015.
3. Dove, Helena. Botany of the Kitchen Garden, Kew Publishing, Royal Botanic Gardens Kew, UK, 2023. 
4. Fanton, Michel and Jude. The Seed Savers Handbook. The Seed Savers Network, Australia, 1993.
5. Green Harvest. (2024). Rhubarb Growing Information. https://greenharvest.com.au/Plants/Information/Rhubarb.html
6. The Heritage Nursery. (2024). Growing Rhubarb in Canberra. https://heritagenursery.com.au/pages/growing-rhubarb-in-canberra
7. Yates Australia. (2024). How to Grow Rhubarb. https://www.yates.com.au/how-to-grow/rhubarb/