Forcing rhubarb: when & how?

Edward

With a passion for growing installed at an early age, I have always been happiest outdoors in nature. After training as a professional gardener and horticultural therapist, I currently run horticultural therapy and community kitchen gardens in the UK, helping others access the many physical and mental health benefits of growing vegetables, fruit and plants.

Favourite fruit: apples and pears
Favourite vegetable: asparagus

Rhubarb tends to crop early in the year from March or April onwards. However, you can try forcing rhubarb for an even earlier and sweeter harvest.

Ornate terracotta rhubarb forcing pots — Forcing rhubarb is achieved by growing it in darkness under cover [Photo: Peter Turner Photography/ Shutterstock.com]

Developed in the early 19^th century, forcing rhubarb (Rheum x hybridum) is the process of growing rhubarb in the dark. When forced, rhubarb produces sweeter and more tender stems than when grown in the light. In Yorkshire, there is an area called the Rhubarb Triangle where forced rhubarb has been commercially produced in heated sheds since the early 1900’s and was awarded Protected Designation of Origin in 2010.

When to force rhubarb?

You can force rhubarb anytime from late December until March when rhubarb is dormant. However, December and January tend to be the most popular time to begin forcing rhubarb, with a crop ready to harvest around 7 to 8 weeks later. If you start early, forcing rhubarb can produce an earlier crop, as depending on the rhubarb variety, regular harvesting of rhubarb begins around March or April.

Rhubarb crown beginning to grow — You can force rhubarb anytime from December until March [Photo: Paul Maguire/ Shutterstock.com]

How to force rhubarb?

In commercial production, rhubarb is moved to and grown in complete darkness in heated sheds. Thankfully, the process for home gardeners is much simpler. All you need is an unperforated large pot or container to place over the rhubarb to exclude the light. Attractive terracotta forcing pots, often used in historical gardens, are available to buy but due to their size, they can be expensive. A cheaper option is to simply use an overturned dustbin or large plant pot with any drainage holes covered over. In reality, it does not really matter what vessel you use, just as long as it provides complete darkness to force the rhubarb.

Step-by-step forcing rhubarb:

Choose a healthy and strong rhubarb plant that has not been used for forcing in the past year and remove any old foliage.
Weed around the plant and apply a thick mulch of compost or well-rotted manure around the crown to help boost stem production.
Place a rhubarb forcing pot over the rhubarb crown making sure that no light can penetrate inside the pot.
Although not strictly necessary, you can insulate the outside of the pot with bubble wrap or straw to speed up the stem’s growth.
If using a large pot in a mild or dry winter, you can occasionally check if the plant needs some water. However, water sparingly as too much can lead to high humidity levels and encourage rot.
After 7 to 8 weeks, check the stem’s progress and begin to harvest them by pulling and twisting the stem off when they are around 20 to 30cm long.
Prepare the stems by removing any leaves and washing and trimming the ends before cooking.
In spring, once all risk of frost has passed, remove the forcing pot.

Forcing rhubarb uses up a lot of the plant’s energy. Once forced, any rhubarb plants should not be harvested from or used for forcing again that year to give them time to recover. For a continuous supply of forced rhubarb every winter, you can grow several rhubarb plants and force them alternately.