In February, a rhubarb crown can look like nothing at all. The leaves are gone, the bed is flat, and the plant seems to have retreated into a knot of roots below cold soil. Then a gardener puts a dark pot over it, waits, and finds red stems rising in the absence of light, tender and bright as if spring had been persuaded to speak in a whisper.
This is forced rhubarb. It sounds theatrical, but the method is simple: cover an established rhubarb crown in late winter so new growth develops in darkness. The Royal Horticultural Society describes forcing as covering crowns to exclude light, producing earlier, paler, more tender stems than outdoor rhubarb grown in full light.1 The plant is not being tricked from nothing. It is spending stored energy.
That is what makes the practice so interesting. Forced rhubarb is a conversation with reserves. The crown gathered energy the previous season, rested through cold, then used that stored strength to push new stems upward before the garden around it had properly begun.
A perennial with a pantry underground
Rhubarb is a hardy perennial vegetable grown for its thick leaf stalks, not for its leaves. Iowa State University Extension describes it as a cool-season perennial that can remain productive for many years when planted in a suitable site.2 The visible plant may vanish in winter, but the crown remains alive below the surface, holding buds and stored carbohydrates for the next flush of growth.
Forcing works because those buds are already prepared to grow. Darkness changes the character of that growth. Without light, leaves stay small and yellowish, stems stretch, and texture becomes softer. The result is not the robust green canopy of May rhubarb. It is a more delicate harvest: pink to red stalks, pale curled leaves, and a milder flavor that belongs to the border between winter and spring.
The crown pays for that early performance. A forced plant has used energy before it has had leaves in the sun to replace it. That is why forcing belongs on mature, vigorous crowns, not young plants still trying to establish themselves.
Choose the crown carefully
The best candidate is an established rhubarb plant that has been growing strongly for several seasons. University of Minnesota Extension recommends waiting until the second season before taking a light harvest and until the third season for a fuller harvest from newly planted rhubarb.3 That same patience applies to forcing. A crown needs reserves before you ask it for an early, shaded crop.
Do not force a weak plant, a newly divided crown, or a rhubarb that struggled through drought, disease, or heavy harvest the previous year. It may still produce a few stems under cover, but you will be borrowing from a small account. Better to let that plant grow normally, feed it, water it in dry weather, and consider forcing another year.
It is also wise not to force the same crown every year. Let forced plants recover by growing in full light after the early harvest, and rotate the practice among several established crowns if you have them. The best forced rhubarb comes from restraint as much as from darkness.
The dark cover
A traditional rhubarb forcer is a tall terracotta cover with a removable lid, but the plant does not require ceremony. An upturned large pot, a clean black nursery container, a bucket, or a lidded bin can work if it blocks light and leaves room for stems to rise. Cover drainage holes if they let in too much light, but make sure the setup does not trap stagnant moisture against the crown.
RHS guidance for forcing rhubarb begins in late winter, when crowns are covered with a forcing jar, upturned pot, or similar light-excluding container.1 In cold climates, adding straw, dry leaves, or another loose insulating material around the outside of the cover can help moderate temperature. The aim is not to cook the crown. It is to create a small, dark, sheltered room just warm enough for growth to begin.
Before covering, clear away soggy debris and check that the crown is not sitting in a wet hollow. A little compost around the plant can be useful, but do not bury the crown deeply. Rhubarb likes fertile, well-drained soil, and the University of Maine Cooperative Extension notes that it does best in a well-drained site with good organic matter.4
What happens under the pot
For several weeks, very little seems to happen from the outside. Inside, buds swell. Stems lengthen toward the top of the dark chamber. Leaves begin to unfold but remain small, puckered, and pale because they are not receiving light. The red color of the stalks becomes more visible because it is not hidden beneath a large green leaf canopy.
Check occasionally, but do not lift the cover every day. Each inspection admits light and cool air. When stems are tall enough to harvest, twist and pull them from the crown rather than slicing through the base. RHS advises harvesting forced stems when they are long enough, usually after several weeks under cover, then allowing the plant to recover afterward.1
Only the stalks are eaten. Rhubarb leaves should not be consumed. University of Maine Cooperative Extension warns that rhubarb leaf blades contain poisonous substances and should not be eaten, even though the leaf stalks are the edible part.4 Trim leaves away from harvested stalks and compost them only if your compost system is appropriate for ordinary plant waste and they are free of disease.
Outdoor forcing or indoor forcing?
Most home gardeners will do best with outdoor forcing in place. The crown remains in the bed, the soil buffers temperature, and the plant can return to ordinary growth once the cover is removed. This is also less disruptive to the root system.
Indoor forcing is possible with lifted dormant crowns, but it is harder on the plant. The crown is dug, chilled if needed, potted or boxed, then placed somewhere dark and cool enough to grow slowly. It can produce beautiful stems, but the crown may be so exhausted afterward that it is discarded or given a long recovery. That makes sense for traditional commercial systems built around forcing beds. It is usually more than a home gardener needs.
In a small garden, the gentler method is enough: choose a mature crown, cover it in late winter, harvest modestly, then let it grow in daylight again.
After the early harvest
Once you have taken the forced stems, remove the cover and let the crown return to ordinary photosynthesis. The plant needs leaves now. They are not ornamental excess. They are how the crown rebuilds the reserves you asked it to spend early.
A forced crown should not be harvested hard again the same season. Let several leaves grow. Keep weeds down. Water during dry spells. Topdress with compost if the soil is lean. University of Minnesota Extension notes that established rhubarb benefits from consistent care and that harvest should stop while enough leaf area remains for the plant to store energy for the following year.3
If the crown seems tired, listen. Thin stems, weak leaves, and slow recovery are signs to skip forcing the next year. Rhubarb is long-lived when treated as a perennial partner rather than a machine.
Why the practice is worth trying
Forced rhubarb is not necessary. Outdoor rhubarb will arrive in its own time, and there is nothing wrong with waiting. But forcing teaches something useful about the plant. It shows how much spring is prepared before spring is visible. It shows how a crown stores last year’s sunlight and spends it as this year’s first growth. It shows that darkness does not stop a plant from moving, but it changes the kind of growth it makes.
There is also the pleasure of the harvest itself. In a season of stored onions, seed catalogs, and wet boots by the door, lifting a cover to find red stalks in the dark feels like opening a letter from the coming garden. It is not a large crop. It is a signal.
Useful rhubarb-forcing supplies
- Pro Cal 10-gallon nursery pot: an inexpensive light-blocking cover if inverted over a mature crown; cover drainage holes if they admit light.
- Clean straw mulch: useful for insulating around the outside of a forcing cover in cold, exposed beds.
- AcuRite soil thermometer: helpful for watching late-winter soil temperature and understanding when crowns are beginning to wake.
Final thoughts
Forcing rhubarb is a small, old-fashioned winter experiment with a serious plant lesson inside it. You are not making growth from darkness. You are revealing growth that the crown has already saved for, then shaping it with shade, shelter, and timing.
Use a strong crown. Cover it late. Harvest lightly. Remove the cover before the plant is exhausted, and let the rest of the season belong to recovery. If you treat the plant generously, the reward is more than a handful of red stems. It is a clearer sense of how perennials remember the previous year underground.
February often feels like the garden’s pause. Forced rhubarb proves that it is also a held breath.
