Forcing Rhubarb for Sweet Early Stems

Forcing rhubarb is one of the simplest, most rewarding tricks in the kitchen garden. Cover a dormant crown in the depths of winter, exclude every scrap of light, and the plant responds by sending up long, slender, candy-pink stems that are sweeter and far more tender than anything you'll pull in spring. You can be picking your own rhubarb in February or March, weeks before unforced crowns have properly woken up. Here is exactly how to do it — and the one rule that keeps your plant healthy for years.

What forcing is and why it works

Forcing simply means tricking a plant into growing earlier than it naturally would, usually by manipulating warmth and light. With rhubarb, the method is almost crude in its simplicity: you exclude all light from a dormant crown.

Deprived of light, the crown still has plenty of stored energy in its roots from last summer, so it starts to grow anyway. But without light it can't produce the green pigment chlorophyll, and it can't toughen up the way an outdoor stem does. Instead the plant pushes its stored sugars up into pale, blanched stalks, reaching frantically for a light source that never comes.

The result is rhubarb that is:

• Sweeter — less of the sharp acidity of outdoor stems, so you need less sugar.
• More tender — the stems are thin, smooth and almost stringless.
• Beautifully coloured — soft pink to crimson stems topped with small, pale, crumpled yellow leaves.

This is exactly the principle behind Yorkshire's famous "Rhubarb Triangle" around Wakefield, where growers force crowns inside dark, heated sheds and harvest by candlelight. You're doing the same thing in your garden, just on a smaller scale and without the candles.

When to force rhubarb in the UK

Timing matters in two ways: the time of year and the age of the crown.

Force in midwinter, roughly January to February. The crown needs a proper cold spell first — rhubarb actually requires a period of winter chill (a "dormancy" rest) to crop well, so you want to wait until it has had a good few hard frosts and has died right back. Covering a crown that has had its winter cold gives the best, fastest response. In a mild winter, or in the warmer south-west, hold off until the plant has clearly experienced some sustained cold rather than forcing too early.

If you cover in early-to-mid January, you can usually start picking forced stems around late February to March, depending on your local climate. You can check typical sowing and harvesting windows for your area on our planting calendar.

Only force an established crown — at least three years old. This is the part beginners most often get wrong. A young plant simply hasn't built up enough root reserves to pull stems out of, and forcing it can set it back or even kill it. Let a newly planted crown grow normally for its first two or three years, building a strong root system, before you ever cover it. A vigorous, mature crown the size of a dustbin lid is the ideal candidate.

For everything on planting, dividing and growing rhubarb the ordinary way, see the main rhubarb growing guide, which this article supports.

How to force rhubarb

You don't need any special kit, though a proper terracotta forcing jar is a handsome (if pricey) thing to own. The job takes about five minutes.

1. Choose and tidy the crown. Pick a strong, established crown. Clear away any old dead leaves and debris sitting over it, but don't disturb the roots. Some growers like to gently loosen the surface soil and work in a little well-rotted manure around (not on top of) the crown beforehand.

2. Cover it to exclude all light. Place a tall, light-proof cover over the whole crown. Your options:

• A traditional terracotta forcing jar — a tall bell-shaped pot with a lift-off lid so you can check progress. Lovely, but expensive.
• An old dustbin, large bucket or bin — turned upside down over the crown. Cheap and just as effective. Weigh it down with a brick so winter winds don't lift it.
• A large pot or stout cardboard box — anything tall enough to let the stems elongate and dark enough to keep light out.

The cover needs to be reasonably tall: forced stems can reach 30–45cm as they stretch for light, so something low will just check them. Block any drainage holes or gaps that let light in.

3. (Optional) Add a little warmth. Light exclusion alone will force rhubarb. But you can speed things up by piling loose straw, dry leaves or strawy manure around and over the cover to trap a little warmth, the way commercial growers heat their sheds. This can bring the harvest forward by a week or two. It's entirely optional — plenty of gardeners just use a bare bin and wait.

4. Wait. Leave it alone and resist peeking too often — every time you let light in you slow the blanching. Check after about three weeks, then every few days.

Harvesting forced stems

Forced rhubarb is ready surprisingly fast. Start picking once the stems are around 20–30cm long — they'll be slim, pale pink and topped with small, pale, undersized leaves.

To harvest, reach down to the base of a stem, hold it low, and pull and twist gently so it comes away cleanly from the crown. Don't cut rhubarb with a knife — the snapped-off stub left behind by cutting can rot and let disease into the crown. Pulling leaves a clean break.

Take stems over a couple of weeks as they reach size. Forcing tends to give a short, concentrated flush rather than a long season, so enjoy it while it lasts — this is the rhubarb for your first crumble of the year.

Once you've taken your forced crop, stop picking and remove the cover. Let the plant get back into the light and grow normally for the rest of the season. Which brings us to the rule that matters most.

The crucial recovery rule

Here is the catch that every forcing guide must be honest about: forcing exhausts the crown. You've made the plant burn through its stored energy early and in the dark, producing stems with no leaves to photosynthesise and pay that energy back. A forced crown comes out of its cover weakened.

So the rule is simple and non-negotiable:

Never force the same crown two years running. After forcing, let the plant grow completely undisturbed for at least one full season — ideally two — to rebuild its reserves before you force it again.

During that recovery year, treat the plant generously: keep it well watered through dry spells, mulch it with compost or well-rotted manure, and resist over-picking even its ordinary spring stems. A crown that is forced too often, or forced while still recovering, becomes thin, weak and unproductive — and may give out altogether.

The neat solution: rotate your crowns. If you grow three or more established crowns, you can force a different one each year on a three-year cycle. That way you get tender forced rhubarb every single season while every plant gets two clear years to recover. It's the same logic gardeners use for crop rotation with vegetables — spread the demand so nothing gets worn out.

If you've only got one crown, the kindest approach is to force it once every two or three years and enjoy ordinary, equally delicious outdoor stems in between. Established plants can be lifted and divided in winter to build up your stock — the rhubarb guide covers how to split a crown so you can grow your way towards that rotating supply.

What next

Forcing is a small bit of theatre that turns a tough, sharp spring crop into something sweet and special weeks ahead of the pack — for the price of an upturned bin. Master the timing, respect the recovery rule, and you'll have your own pink, tender stems on the table by early spring, year after year.

From here, it's worth reading the full guide to growing rhubarb for planting, feeding and dividing, and browsing the wider grow fruit section for other easy soft fruit to pair it with. If you're still building up your plot's fertility, improving your soil is the single best thing you can do for stronger crowns and better stems.