How do I force rhubarb for early stalks?

Forcing is one of the few genuinely magical things in a vegetable garden: you cover a dormant crown in January and lift the pot in February to find a bundle of pale pink stalks that taste noticeably sweeter than anything the plant produces later. It costs the plant a great deal of energy, which is the whole basis of the rules around it.

Step by step

1. Use an established, healthy crown.Force only a plant that is at least three years old and growing strongly. A young or weak crown may not recover at all.
2. Wait until the crown has had a proper cold period.Rhubarb needs winter cold to break dormancy properly. Cover it from around the turn of the year rather than in autumn — forcing too early gives a poor, slow response.
3. Clear and tidy the crown first.Remove last year's dead leaves and any debris so slugs have nowhere to hide under the cover, and give the crown a mulch of well-rotted manure around it.
4. Cover it completely and exclude all light.A traditional terracotta forcing pot, an upturned dustbin, a large bucket or a tall plastic tub — anything tall enough for the stalks to extend into and completely light-proof. Block any drainage holes.
5. Weight the cover down.Wind lifts a light bin easily, and a few hours of light will green the stalks. Put a brick or a slab on top.
6. Insulate around it if you want to speed it up.Packing straw, leaves or manure around the outside of the cover adds a little warmth and brings the crop forward, which is how the commercial forcing sheds work.
7. Check after about four weeks.Lift the cover briefly. Stalks are usually ready at four to six weeks, when they are 30cm or more, pale pink and topped with small crumpled yellow leaves.
8. Pull the forced stalks over two or three weeks.Twist and pull them out as with normal rhubarb. Take the crop and then stop — do not keep the plant covered hoping for a second flush.
9. Remove the cover and leave the crown alone for the rest of the year.This is the rule that matters. Take nothing else from that crown for the whole season and let it grow freely all summer to rebuild.
10. Do not force the same crown again for three years.Forcing takes a lot out of a plant. Rotate between crowns, or accept a three-year gap between forcings on a single one.

Tips

• If you only have one crown, alternate: force it one year, then leave it entirely alone for the next two.
• Forced stalks cook down faster and need less sugar than main-season rhubarb — they are sweeter and far more tender.
• A terracotta forcing pot is beautiful and expensive; a black dustbin works exactly as well and warms up faster.
• Slugs love the warm dark environment under a forcing cover. Check when you lift it and clear them out.
• The pale crumpled leaves on forced stalks are just as toxic as normal rhubarb leaves — cut them off and compost them.

Common mistakes

• Forcing a young or weak crown — It has no reserves to draw on and may not recover. Force only established, vigorous plants.
• Picking normally from a forced crown later in the year — The plant has already given up a great deal of stored energy. Taking more in the same season sets it back for years.
• Forcing the same plant every year — It declines rapidly. Three years between forcings on the same crown is the working rule.
• Using a cover that lets light in — Light greens the stalks and destroys the point — you get thin ordinary rhubarb rather than tender pink forced stalks.

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