STRIKING A balance between ventilation and frost protection is the key to successful late-season beet storage, says British Sugar.

Well-managed clamps should have temperatures of 0-10C, says project manager Jonathan Pilbrow.

“The idea is to have good enough ventilation to stop temperatures from rising too high, but sufficient frost protection to ensure beet are not frozen and damaged.”

Big bales make excellent clamp walls and offer good frost defence, he says. “But they can stop rainwater draining away, so placing them on pallets is a good way of getting drainage.”

There is no need to block the air gaps between the pallet boards. Even if temperatures fall below freezing, frost will not penetrate the clamp too far, he adds.

Clamp walls 2.5m (8ft) high will stop frost entering clamps. “But in mild weather, they will prevent heat escaping and may create hot spots”. A better solution is to use a bale wall only 1.2m high, together with a clamp cover.”

Very exposed sites may justify a 2.5m retaining wall on the east or north face, he says.

Clamp sides should be covered when air temperatures are forecast to drop below -2.5C for more than one night, and the tops should be covered if -3.5C is predicted, advises Mr Pilbrow.

“It’s important to remove covers once the frost risk has passed to prevent heat build-up.”

Suitable covers include straw, but it is labour-intensive to use. Polypropylene sheets are good insulators, easily applied and removed, but need at least two people to handle them in windy weather.

Polyfelt material is best, he says. “It’s lighter and easier to handle, provides good insulation and allows air to pass through. If you look after the sheets and store them well when not in use, they”ll last for ages. Don”t opt for plastic – it doesn’t breathe and the beet will heat and swell up.”

Optimum clamp size is 2.5m high, 10m wide and long enough to accommodate the beet volume. Clamp surfaces must be flat and free from frost pockets.