How To Force Rhubarb – 3 Techniques You Can Use

A candle at the center of growing rhubarb in forcing shed.

Forcing is an excellent technique you can use to stimulate rhubarb that goes dormant in winter to grow out of season.

Covering to prevent light from reaching the crown will encourage rhubarb to make an early growth, and when the forced stalks are about 20-30cm long, it is the ideal time to harvest and use in cooking.

However, it is best to force established rhubarb only. Young plants don’t have sufficient energy to generate early stalks, and the following growth might be compromised.

You can do the forcing method both indoors and outdoors to generate harvest out of season. Forced rhubarb is sweeter and softer compared to the ones harvested in early summer.

Oxalic acid is the compound giving the sour taste to the rhubarb. Shutting the light out, and enclosing to increase the plant’s surrounding temperature will reduce the oxalic acid in the stems. The process will result in sweeter, thicker, and tender stems with a delicate flavor.


3 Ways To Forcing Rhubarb For An Early Harvest


1) The Traditional Garden Way

Terracotta forcing pots in the garden.
Image by: Peter Ashton-Wikipedia

The traditional garden method is the most common way to force rhubarb. It is typically done by covering the crown with a bucket or any type of forcer early in the year to make the rhubarb grow a bit earlier to provide tender and straight stems.

However, this method makes the plant grow in a cold atmosphere, cold soil, and frosty weather. You need to lift the lid every time you want to check its growth.

Step #1 – Growing Rhubarb From Seed

  • If you grow rhubarb from seed, you have to wait about 2-3 years for the plants to establish before forcing them to generate stalks during out of season.
  • It should begin its life with two to three years in the open fields to allow the plants to build up its roots and store sufficient energy to rely upon during the forcing process.
  • It usually takes 7-8 weeks,  and about 20-30 cm long for the stalks to become big enough for harvesting.

Step #2 – Provide The Appropriate Forcer

  • Find a cover adequate to block light as you cover the plant. You can pick either a purpose-made rhubarb forcer or get a tall bucket to create sufficient darkness for the rhubarb crown.
  • Providing total darkness along with the heat generated inside the pot can encourage the plants to grow faster, as they try seeking for some light.
  • By obstructing the light, rhubarb continues to grow while maintaining its tender shoots.
  • The stems usually appear pale due to the lack of chlorophyll, a pigment involved in photosynthesis that provides energy and color to the plants.
  • Crowns exposed to too much light will cease to grow and the photosynthesis will then give the plant a sour bitter flavor.

Step #3 – Add Supplemental Nutrients

  • To boost its nutrients and achieve its potential growth, toss some well-rotted manure or compost around the base of the crown.
  • Ensure to clear the area from any existing debris, weeds, or any other plants surrounding the rhubarb crown before you place down the forcer pots.

Step #4  – Deprive All Possible Light

  • Cover the entire crown with your forcer. Ensure to plug any possible holes or cracks to prevent light from reaching the rhubarb.
  • You can also insulate the pot by covering the outside with some old carpet, bubble wrap, or hay and straw if you want to speed up the forcing process.

Step #5 – Continue To Water And Fertilize

  • Rhubarb are heavy feeders, and it has no way of absorbing nutrients it requires if the soil is too dry.
  • Make sure to water and add supplemental nutrients for a much better chance to survive.

Step #6 – Harvest And Let The Plant Recover

  • It is easy to harvest full-grown stems. Just pull them gently from the base of the crown, remove the leaves, and wash them thoroughly before cooking.
  • Avoid cutting the stalks when you harvest, or you may promote disease within the cut portion.
  • The process of forcing the rhubarb will weaken the crown, resulting in weak new stem growth.
  • It is best to feed more nutrients by adding compost at the base of the crown after the harvest to ensure a more sustainable return.
  • Harvesting more from the crown used for forcing during summer or the following year is not beneficial to the plant’s health.
  • Allow the crown to recover energy naturally in the garden before you force them again if you wish to.

2) Forced Rhubarb In Heated Forcing Sheds

Growing rhubarb in a forcing shed.

Another way to force rhubarb is to dig up the crown in winter and bring it into a warm dark place. This method is appropriate to force rhubarb in large quantities.

The use of forcing sheds in winter, heated with cheap coal to trick the rhubarb into growing is proven to be helpful, particularly in Yorkshire where many sheds from coal mining remain. Produce in large quantities allow people to eat and enjoy rhubarb all year round.

Forcing is popular in Yorkshire as many people love rhubarb crumble due to its healthy properties and easy-to-grow methods at home.

But modern forcing sheds are now using gas to heat. Growers allow the plants to grow first in the open field for about 2-4 years for the crown to develop and store up sufficient energy.

The crowns are then lifted and stored in low roofed, heated forcing sheds. The warmth produced triggers growth, and the total darkness encourages long tender stalks.

Rhubarb can develop quite fast in forcing sheds and you can actually even hear them making strange sounds while growing.


3) Forcing Rhubarb In A Barrel

The third method you may be interested in is forcing rhubarb in a barrel inside the greenhouse. Although this method does not use an artificial heater like the forcing sheds, it is still much warmer compared to outside.

If your rhubarb already needs splitting, then this option is best for you. Rhubarb usually needs splitting every five years because they tend to get so big.

Split and chop one large section so you can use it for forcing in your barrel, leaving the other chunk of the crown in the ground to grow again.

Forcing rhubarb in the winter can extend its growing season, giving you fresh homegrown produce for a year or even a little bit longer.

To force rhubarb in a barrel:

  • Dig up rhubarb in early winter and place in a small plastic barrel.
  • Cover with a piece of cloth.
  • If a barrel is not available and you don’t have a greenhouse, place the crown in a bin liner and cover with a dark cupboard to provide total darkness.
  • The temperature in the barrel should be much higher than the greenhouse, so ensure the barrel has no holes for light to penetrate inside.
  • The cloth will keep the warmth and humidity inside the barrel while allowing excess moisture to evaporate. It will likewise create the total darkness the plant requires to encourage the plants to grow fast upward.
  • Sprinkle a little amount of water when the plants begin to look dry.
  • Leave the barrel in an unheated greenhouse for some time. The warmer conditions are sufficient enough to trigger growth even in winter.
  • Once the shoots start to emerge, they will develop quickly into long tender stems and provide you with a small amount of harvest at first, and gradually give you plenty as the weather starts to warm up.
  • The amount of harvest you get also depends on the variety of your rhubarb, as some force quicker than others.
  • Forcing rhubarb in a barrel is inexpensive and maintenance-free. It requires no weeding and no fuel cost.

The Best Material: Terracotta Forcing Pots

A row of terracotta forcing pots in a garden.
Image by: telegraph.co.uk

Commercially, forcing rhubarb is usually done in warm, dark sheds to produce candy pink, sweet stems. Forcing rhubarb at home is usually done with the use of terracotta pots specifically designed to force the plant.

Terracotta pots used for forcing rhubarb are attractive additions to your vegetable patch. They usually have a small lid you can use to take a peek and see how your rhubarb is doing.

But terracotta is susceptible to fractures and may shatter if left out in the freezing winter for some time. You should store yours somewhere dry and frost-free during the winter and then put back into place in late winter when the crown starts to swell.

If you are on a limited budget and are hesitant to buy a forcer, anything you can cover the crown to shut the light out will work. You can try using an old bucket or an old chimney pot with a saucer on top to cover.

But there’s one thing you have to keep in mind – try not to force the newly planted crown. You need to wait about 2-3 years and let the plant grow in the open field. Also, it is not a smart approach to force a single head in a row.

If you have adequate space to grow, it is worth having two or more crowns of rhubarb so you can force the plants in alternating years.


Final Thoughts On How To Force Rhubarb

Forcing is a simple way of tricking plants into early growth by adding a little warmth, and often the results are impressive.

Lifting of your rhubarb crowns and bringing them in the forcing sheds will allow you to enjoy rhubarb delicacies a whole month earlier.

The pale stems of the forced rhubarb need less sugar to balance their tartness than those of the non-forced rhubarb. And in addition to that, forced rhubarb has an exceptional tenderness you will surely love.

You can opt to buy terracotta forcing pots if you like. They come with a lid where you can take a peek and see how your awaited stems are coming along.

However, if you have a limited budget, any covering or bucket will work fine as long as it completely obstructs light from reaching into the crown.

Another thing you have to remember is to keep the crown slightly moist. Dryness is also one of the reasons why the stems stop growing. And it usually takes several weeks before you can harvest the stalks.

One more thing that you have to keep in mind when forcing rhubarb is that newly forced crowns should be left to regain energy for the following year. The forcing process weakens the plants, making them susceptible to various diseases.

If you wish for a continuous supply of rhubarb, then it is best to have two or more plants on the go and force them in alternating years.

Excellent reconditioning is to ensure the plants get the appropriate rest period to recover. This will eventually result in healthy growth and thicker stems.

There you have all the reasons why forcing rhubarb is beneficial to you, along with all the helpful techniques you can follow to force it successfully.

Any suggestions you would like to add? Please don’t hesitate to write your thoughts down in the comment section below. We’re always happy to read them!

About Benita Abucejo

Hi there! My name is Benita Abucejo. What can I say? I truly love spending my days in the outdoors, specifically in the garden. Gardening has always been a strong passion of mine since I was a little girl. It has brought me so much joy and happiness that it is definitely safe to say that I will be a gardener for life. For a period of time, I was able to work with people who are into home gardening and I found it to be quite beneficial to my physical health, as well as my mental well-being. Here at Seasonal Preferences, I am going to share with you my experience and ideas so that you can fulfill yourself with the same satisfaction and happiness. Of course, if you have ideas, I would love to hear those as well! Being creative in the garden can really be quite fascinating so let's share our experiences and be the best gardeners we can be. With that being said, thank you for dropping by and please leave me a comment on one of my posts if you would like to get in touch!

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