What is Rhubarb Forcing and Why Do It?
Forcing rhubarb is a traditional gardening method used to encourage the plant to produce tender, bright red stalks significantly earlier than its natural outdoor growing season. By simulating spring conditions in the dead of winter, you can enjoy this tart fruit (botanically a vegetable) months ahead of schedule, often from late winter or early spring.
- Forces earlier, sweeter rhubarb stalks.
- Extends enjoyment beyond the main season.
- Requires darkness and mild warmth.
- Uses established rhubarb plants.
The primary motivation behind forcing rhubarb is to gain access to its prized early growth. These forced stalks are typically more tender, less fibrous, and possess a sweeter flavour with a more delicate tartness compared to those grown exposed to the elements. This is because the plant expends its stored energy reserves to produce these initial shoots, which are protected from harsh weather and pests. It's a clever way to get a head start on the culinary season, bringing fresh, homegrown produce to your kitchen when other garden options are scarce.
Understanding the plant's biology is key. Rhubarb is a hardy perennial that requires a period of winter dormancy, characterised by cold temperatures and shorter days. Forcing exploits this by providing a warmer, darker environment after the plant has undergone sufficient chilling. This artificial 'spring' signals the plant to break dormancy prematurely, sending up succulent shoots from its crown.
The problem faced by many gardeners is the limited window for enjoying rhubarb. By the time it's naturally ready outdoors, the season can be fleeting, and later harvests can become tougher. Forcing rhubarb directly addresses this, offering a solution to prolong the availability of this versatile ingredient for desserts, crumbles, and sauces.
Protect your established rhubarb plants before the first frost by mulching heavily with straw or compost to insulate the crown and provide nutrients for future forced growth.
Forcing rhubarb is not about growing new plants from seed or cuttings specifically for this purpose. It relies on mature, well-established rhubarb plants that have been in the ground for at least two to three years, allowing them to develop strong root systems and sufficient energy reserves. This makes it an accessible technique for most gardeners with existing rhubarb patches.
Methods for Forcing Rhubarb
Several methods can be employed to force rhubarb, each designed to create the essential conditions of darkness and mild warmth. The most common approaches involve using containers or covering existing plants in situ. The goal is to trap heat and exclude light, tricking the plant into rapid growth.
Using a Rhubarb Pot or Cloche
This is a popular and effective method. A dedicated rhubarb forcer, often made of terracotta or plastic, is placed over an established rhubarb crown in late autumn or early winter, once the plant has died back naturally and experienced some cold. The pot is typically sealed at the top with a lid or a piece of wood. Alternatively, a large bucket, dustbin, or even a sturdy cardboard box can be used, provided it completely covers the crown and is secured to prevent light ingress. Placing straw or stable manure around the outside of the pot can add insulation and gentle warmth as it decomposes, further encouraging growth.
Creating a Simple Dark Shelter
If a specialised pot isn't available, you can construct a temporary shelter. Build a simple framework of stakes around an established rhubarb crown and cover it with opaque material, such as thick black plastic sheeting, old carpet, or even thick hessian sacks. Ensure there are no gaps where light can penetrate. This method works best when combined with a layer of straw or compost placed on the ground inside the structure, which will generate a small amount of heat.
The 'Bucket and Mound' Technique
For gardeners with many crowns, a simpler, albeit less controlled, method involves mounding soil or compost over the dormant crowns. In late autumn, after the foliage has withered, cover the entire crown with a thick layer of compost, soil, or straw, piling it up to create a mound. This insulates the crown and encourages it to break dormancy. While this might not produce stalks as early or as vividly coloured as covered methods, it does offer a way to encourage earlier growth across a larger area.
Crucially, never force a plant that is not fully dormant. Wait until the leaves have died back naturally after the first hard frosts. Attempting to force a plant that is still actively growing or not sufficiently chilled will be ineffective and can weaken the plant.
The success of forcing rhubarb hinges on creating a controlled environment that mimics the onset of spring after a necessary period of winter rest.
When forcing, it is vital to monitor the conditions. While darkness is essential, excessive heat can be detrimental. The ideal temperature range for forcing is typically between 7-15°C. If temperatures soar, especially on sunny days, ensure adequate ventilation by briefly lifting the cover, but always re-cover it promptly.
Harvest forced rhubarb carefully. Twist the stalks gently at the base and pull them away from the crown. Avoid cutting, as this can damage the plant and hinder future growth.
The choice of method often depends on the number of rhubarb crowns available and the resources at hand. For most home gardeners, a single rhubarb pot or a DIY cloche over a healthy plant provides the best balance of effort and reward.
Harvesting and Using Your Forced Rhubarb
Once your rhubarb has been forced, the harvest period typically begins within eight to ten weeks, depending on ambient temperatures and the specific forcing method used. You will notice the characteristic bright red, tender shoots emerging from the darkness. The key is to harvest them at the right time to maximise their flavour and tenderness, and to ensure the plant can recover for future growth.
When and How to Harvest
Look for stalks that are about 15-25 cm (6-10 inches) long and have unfurled their leaves. Harvest only what you need at any one time, and aim to stop forcing from a particular crown once the stalks start to become thinner or less vigorous. This usually happens after a few weeks of harvesting. The plant needs to be allowed to recover and photosynthesise if exposed to light again. To harvest, gently grasp the base of a stalk and twist it, pulling it away from the crown. This method avoids damaging the delicate buds at the base, which are essential for future growth. Never take all the stalks from one crown; leave some to allow the plant to continue its natural cycle.
Post-Forcing Care
After you have finished harvesting from a forced crown, remove the forcing pot or cover, allowing the plant to receive light and air. Ensure the plant is well-watered, especially if the weather is dry, and apply a good mulch of compost or well-rotted manure around the base. This replenishment of nutrients and moisture is vital for the plant's recovery and for building up reserves for the next growing season, including potential forcing in the following year. A forced rhubarb plant will usually still produce a normal crop later in the season once it's growing outdoors again, though it might be slightly reduced.
Remember that forcing is a temporary measure that draws on the plant's stored energy. It should not be done every year on the same crown, or for too long a period, to maintain the plant's long-term health and vigour. Alternating which crowns you force each year is a good practice.
The resulting forced rhubarb is incredibly versatile in the kitchen. Its sweetness means less sugar is often required in recipes. It’s ideal for early crumbles, pies, fools, and compotes. The vibrant colour makes it visually appealing, and its tender texture is perfect for delicate desserts. Consider pairing it with fruits like strawberries when they become available, or using it in more savoury applications like chutneys or sauces for pork or duck.
Alternatives to Forcing
While forcing offers the earliest harvest, other methods can also extend your rhubarb enjoyment or provide similar early-season tartness. Planting different varieties known for producing earlier or more vigorous growth can naturally shift your harvest window. For instance, varieties like 'Timperley Early' are specifically noted for their early cropping. If you're interested in growing other early produce, consider planting crops like spinach, radishes, or certain types of lettuce under cloches or in a cold frame to get them started ahead of the main season.
For those interested in extending their fruit harvest, planting early-fruiting strawberry plants in pots or containers that can be brought into a sheltered spot or cold greenhouse can yield fruit not long after forced rhubarb appears. Similarly, early-season blueberry bush varieties might offer fruit sooner than expected with good care. If you wish to grow rhubarb but lack space for traditional crowns, growing strawberries in pots is a much more compact alternative.
Troubleshooting and Preventing Issues
While rhubarb forcing is generally straightforward, a few issues can arise. Understanding these potential problems and their solutions can help ensure a successful early harvest and maintain the health of your rhubarb plants.
Common Problems and Solutions
Lack of Growth: If your forced rhubarb isn't growing, the most likely cause is insufficient winter chilling. Rhubarb needs a period of cold temperatures to break dormancy effectively. If your winter has been unusually mild, the plant may not be ready to force. Another cause could be inadequate stored energy; ensure your plants are well-established and have been fed and mulched appropriately. Check that the forcing environment is dark enough and not too cold.
Poor Colour: While forced rhubarb is known for its red colour, some varieties naturally produce greener stalks, even when forced. If you are aiming for vibrant red, ensure you are using a suitable variety and that the forcing conditions are consistently dark. Light exposure during growth will lead to greener, tougher stalks.
Weak or Thin Stalks: This can occur if the plant is not mature enough, has been forced for too long, or if it's being forced too frequently. As mentioned, forcing draws heavily on the plant’s reserves. Over-forcing or forcing annually without adequate recovery time will deplete these reserves, leading to weaker growth. Alternating which crowns are forced and ensuring a good feeding regime after forcing is crucial.
Pests and Diseases: While forcing protects rhubarb from many external pests, issues like slugs can still be a problem in damp, sheltered conditions. Inspect your forced rhubarb regularly and remove any pests. Ensuring good air circulation when possible (briefly lifting covers) can help prevent fungal issues.
Preventing over-reliance is key to long-term rhubarb health. Force a plant for no more than 4-6 weeks, and ideally, don't force the same crown year after year. This allows the plant to recover and build strength for its natural outdoor season.
When considering other garden projects, remember that techniques like pruning raspberries or pruning grape vines require specific timing and knowledge to be effective. Rhubarb forcing, by contrast, is a more forgiving process, primarily requiring attention to light, temperature, and dormancy.
By understanding the needs of your rhubarb plants and applying the principles of forcing correctly, you can reliably extend your harvest and enjoy this delicious early-season produce. The satisfaction of harvesting tender, homegrown stalks when the garden is otherwise dormant is a reward in itself.