Growing Rhubarb

Recently we’ve been admiring the rhubarb grown on the other plots and decided that we HAVE to grow some. Saying that, I know absolutely nothing about rhubarb apart from I love it in crumbles, pies and fools. So, I’ve been busily researching it and here are my findings.

Rhubarb is a hardy perennial that belongs to the Polygonaceae family. It has interesting relatives; this family contains some of the world’s worst weeds, including Japanese knotweed! It’s an architectural plant with large vibrant green leaves on the end of long stalks of varying colour ranging from red, pink to soft greens.

Rhubarb originates from China, Russia and the Himalayas. Its generic name is thought to come from Rha, the ancient name for the River Volga in Russia, where rhubarb grew in abundance on the riverbanks.

Rhubarb is botanically a vegetable despite being used in many puddings. Although rhubarb is an ancient plant, widespread culinary use only began about 200 years ago. Historically the use of rhubarb has been medicinal. Over 5000 years ago Chinese herbalists ground up dried rhubarb roots into powder. This powder was used as a laxative.

Marco Polo talks about the Chinese rhubarb rhizome in his journals following his travels to China. It’s thought rhubarb was grown in Italy as early as the 1600’s. Rhubarb only came to British shores in the 1760’s. It gained popularity in the late 1800’s when the Sugar Tax was repealed in 1874.

Growing Rhubarb

Rhubarb can be grown from seed but it doesn’t always come true. The best choice is to use existing rootstock. Rhubarb is sold as crowns or plants. These can be bought in the local garden centre in the spring. The more unusual varieties can be found online from rhubarb specialists. This is our ‘Timperley Early’ rhubarb plant, planted this week.

Expect rhubarb plants to live for around 7 to 10 years, although some plants live much longer. As the plants will be in situ for a long time it’s worth preparing the ground properly. They are thirsty plants and rather greedy feeders so ensure lots of organic matter is dug deep into the planting space.

It’s best to plant in the spring or autumn when the soil is warm and moist. Saying that, rhubarb can be planted at anytime of year providing the ground isn’t frozen or waterlogged, or if there’s a drought. Rhubarb prefers to be in a sunny or partially shaded position in fertile, moist, free draining soil.

Rhubarb thrives when the summers are damp and the winters are cold and dry. Rhubarb requires an extended period of cold weather, temperatures below 40F for dormancy and temperatures above 40F to 75F to stimulate vigorous spring and summer growth. Temperatures above 90F slow down growth rates and growth may stop completely as the plant becomes stressed when too hot.

Our plot has heavy clay soil and despite digging in plenty of organic matter there is still a tendency for the soil to get a little waterlogged. Whilst rhubarb enjoys moisture, it hates to be waterlogged, especially in the winter. Typically when planting, it’s advised to plant the crown one inch below the soil level. However, given the heavy clay soil, we will plant them slightly higher, so the crown sits at soil level. This will help prevent crown rot. Don’t plant rhubarb crowns too high, as this will dry them out.

As rhubarb plants grow large, some varieties grow as much as 4 to 5 feet wide, space each crown at least 100cm apart.

Maintenance

Once planted, rhubarb is pretty low maintenance. Keep the area weed free and water well during dry spells.

In the spring feed the plants with a general fertilizer and apply a mulch to help retain moisture.

In the autumn the plants leaves die back naturally. Remove all the old rhubarb stalks leaving the buds exposed to the cold winter weather. Apply mulch around the plant taking care not to cover the crown.

As rhubarb is a hardy perennial it is a good practice to divide the plant every 5 years or so to maintain the plants vigour. If the crowns become over crowded the plant may become weak. The best time of year to do this is usually between November and March when the plant is dormant.

How to divide plants.

Use a spade to remove the crown. Then split the crown into three or four pieces, ensuring each section has a piece of rhizome (thickened root) and at least one, but ideally 2 to 3 healthy growing buds.

Perennials produce new growth on the outer edge of the crown. These sections are likely to be healthier and more vigorous than the centre of the plant. In fact, it’s best to discard all the old woody growth from the centre of the plant.

Replant straight away. It this isn’t possible wrap the plant in damp material until ready to replant. Don’t allow the roots dry out.

Harvest

It’s really important not to remove any stalks during the first year of growth. This will allow the plant to produce plenty of nutrients to build up in the plant roots for next year’s growth. Unless the plant is particularly vigorous, then maybe only lightly pick stalks in the second year until the plant is fully established.

Once the plant is established, the general rules are to pick only a few stalks at a time, and never more than half all in one go. Leave enough active foliage on the plant so it can continue to generate sufficient fuel otherwise this will seriously compromise next year’s growth.

Rhubarb is usually ready to harvest in March all the way through to July or August depending on temperatures and variety. Rhubarb growth slows as temperatures rise above 75F and stop growing completely at temperatures above 90F. In the summer, stalks will get shorter and thinner; this is a sign that growth rates are slowing, and it’s time stop to harvesting stalks. It’s also thought that picking stalks beyond mid summer will lead to a reduction in next years crop.

Mature plants can typically be harvested over an 8 to 10 weeks period. Expect 2 to 3 pounds of stalks per plant.

When removing a stalk from a rhubarb plant, it should be pulled out rather than cut out. Rhubarb is highly susceptible to rotting. Leaving a section of the stalk on the plant is likely to promote rot and damage the health of the plant.

To pull a stalk from a rhubarb crown, place your index finger down the inside of the stalk right down to the base. Grip the back of the stalk with your hand. Pull slowly but firmly and twist at the same time, the stalk should come away fairly easily!

The leaf is inedible and should be discarded. Throw it on the compost heap. Rhubarb leaves contains high concentrations of oxalic acid. Rhubarb became infamous in the First World War as soldiers were given rhubarb leaves as vegetables. It killed many of them, poisoned by oxalic acid. Saying that, it’s worth leaving a portion of the leaf attached to the stalk, about 2 to 3 inches. This will help to keep moisture in the stalk so it should stay fresh and crisp for longer. Just remember to remove the leaf before consuming!

If the stalks are soft and mushy then don’t eat them. The stalks may have been damaged by severely cold weather. Extremely cold weather can cause the oxalic acid crystals in the leaves to migrate to the stalks rendering them poisonous.

Potential Problems

Fungal Disease – Crown Rot

Poor soil drainage may lead to a fungal disease, crown rot. The diseased buds on the crown produce weak spindly stalks and the leaves will appear limp. If this happens, dig up the plant and remove all infected areas. Don’t replant the healthy sections of the plant in an area that has been affected by crown rot.

Flower Stem

In the spring the plant may produce a flower stem. It looks a little like sprouting broccoli.

Looking around the allotments, there are plenty of flower stems on the rhubarb plants this year. It typically happens on older plants; plants that are three years or older. These should be removed straight away so all the plants energy is directed into stalk and leaf production rather than setting seed.

Using secateurs cut the flower stem as close as you can to the base of the plant. Try not to leave much of the flower stem on the plant, as this will encourage rotting and pesky pests such as slugs. Both of which will damage the health of the plant.

Thin Weak Stalks

This may be a sign that the plant is losing vigour and needs to be divided. Increased feeding may also help.

Split Stalks

This can be caused by erratic growth due to sudden and rapid seasonal changes. For example cool dry periods followed by moist mild weather my cause a sharp spurt in growth causing the existing hard outer growth to split.

Bad tasting Stalks

It’s best to harvest rhubarb while the days are cooler and damp. Warm, dry summers can result in poorly coloured, bad tasting stalks. Time to stop harvesting when you notice this.

Pests

If the summer is dry and hot, flea beetles may damage newly planted rhubarb as they feed on the tender leaves.

The rhubarb curculio beetle occasional attacks plants. It’s a large dark beetle, covered with a dusty yellowish coating and looks rather like an anteater. (See below)

WARNING: Not for the faint of heart!

The adult beetles appear around mid May through to early summer. The beetle punctures the leaf stalks as they feed and lay eggs. These eggs won’t hatch in rhubarb because the rapidly growing stem tissue crushes them. So if you notice holes in the stalks, the chances are that particular rhubarb stalk may not be strictly vegetarian!

Leaf spot

This is a fungal disease. The spores overwinter on old rhubarb leaves and stalks. By removing the foliage and stalks in the autumn this should help prevent this disease.