8 Step Rhubarb Forcing Routine with Timperley Early Crowns Under a Terracotta Cloche

Crown age before the forcer

A Timperley Early crown pushed into growth before its third growing season rarely recovers well. The blanched stems are fed by reserves stored in the rhizome, and a two-year-old plant has usually built too small a carbohydrate store to fund a forced flush and then refill itself. Commercial growers in the Yorkshire Rhubarb Triangle around Wakefield usually give crowns two to three years of field growth before lifting them for the forcing sheds. The same calculation applies in a garden bed.

Use weight and bud size as the test. Lift a possible crown in late autumn and look for three or four fat dormant buds on a rhizome about the diameter of a clenched fist. Smaller crowns should grow on for another year. Forcing spends the plant hard, so a crown forced under a terracotta cloche in January should be left entirely unharvested the following summer. Gardeners with three or four crowns can rotate the job and avoid wearing out one plant.

Steps one and two: bank the winter cold

Forcing depends on chilling first. Rhubarb needs a sustained spell below roughly 5C to break dormancy properly, and Timperley Early is valued because it satisfies that chilling requirement faster than many varieties. That is why it leads the season.

The first step is patience. Leave the crown exposed through early winter frosts. Across much of the UK, the bare crown takes December cold without any cover.

The second step is covering at the right moment. After several hard frosts, often by the first week of January in southern England and about a fortnight later further north, the chilling requirement is usually met. Clear away old foliage and slug-harbouring debris before sealing the crown in. If the cover goes on too early, the crown often produces slow, thin stems. Cold triggers the process.

Step three: choose the cover

A traditional terracotta rhubarb forcer is a tall bell, roughly 45 to 60cm high, with a removable lid. The lid lets you inspect growth while limiting light, which keeps the stems pale and tender.

An upturned bucket or galvanised dustbin can exclude light, and many allotment crowns are forced that way. Terracotta has one clear advantage: its porous wall moderates temperature swings and allows a little moisture movement, reducing overheating on bright cold afternoons and stale damp around the crown.

Steps four and five: darkness, warmth, and speed

Light exclusion produces blanched pink stems. Warmth controls how quickly those stems lengthen.

Step four is to set the forcer cleanly over the crown. Check the base for gaps, because even a thin line of daylight can green the stem tips and toughen the growth. Keep the lid on except during inspection.

Step five is optional, and it is the technique that gives the Rhubarb Triangle its reputation. Fresh stable manure or a thick collar of half-rotted compost packed around the outside of the terracotta forcer gives off gentle heat as it breaks down. That heat can lift the temperature inside the cover by several degrees.

At an internal temperature near 10C, stems usually extend slowly and may take four weeks or more. With active manure banked around the forcer, the inside can move toward 15C, and the same crown may produce pullable stems in under three weeks. Faster forcing draws more heavily on the crown’s stored reserves, so the warmest regime also makes the following fallow summer more important.

There is a ceiling. If the internal temperature rises much past 18C, the stems can become thin, pale, and prone to rot, because the crown cannot supply enough water and sugar to fill them properly. A soil thermometer pushed under the rim once a week gives a direct reading of the conditions inside the cover.

The manure collar should warm the forcer, not bury the plant’s centre. Keep the active material outside the terracotta wall and away from the buds. The crown needs heat around it, darkness above it, and enough air in the soil for new growth to stay sound.

Step six: water lightly

A forced crown is growing actively, and terracotta wicks moisture from the enclosed space. The soil under the forcer should never dry to dust. One watering can of about four litres applied to the surrounding soil when the cover goes on, followed by weekly checks, is usually enough through a cool January and February.

Too much water causes more trouble than too little in this setup. Cold, saturated soil under a sealed forcer is a common route to crown rot. The damage stays hidden until the lid is lifted and the enclosed space smells of decay, with softened tissue around the buds.

Step seven: pull the stems cleanly

When the stems reach 20 to 30cm, pale pink and crisp, they are ready to harvest. For Timperley Early under a warmed forcer, that usually comes three to four weeks after covering. Pull each stem with a twist at the base. A clean pull removes the whole stalk with its sheathing base and leaves no wet stub that can rot back into the crown. A knife cut leaves wet tissue behind.

Harvest over two or three weeks as stems lengthen. Discard the leaves, since the oxalic acid that makes rhubarb leaves inedible is concentrated there. The stalks remain within safe limits. Stop pulling once the crown’s output visibly thins, because stripping the last weak stems spends reserves the plant needs for recovery.

Step eight: give the crown its recovery year

Lift the forcer in early spring, scrape away the manure collar, and let the crown green up in full daylight. From that point, leave it alone for a full season. No stems are pulled that summer.

A spring mulch of well-rotted compost helps the crown rebuild. Keep the mulch clear of the central buds. Let the foliage die back naturally in autumn, so the plant can move reserves down into the rhizome.

This is the step that gets skipped most easily. A crown forced two winters in succession with no fallow period declines quickly, sending up thinner stems each season until it fails. A rotation of three or four crowns lets one plant force while the others grow on. Wakefield growers replace shed crowns entirely after a single forcing because they choose production over a recovery year. That replacement habit is the plainest measure of how much one winter flush takes out of a crown.