W hat's wassailing? Find out about the ancient Somerset tradition which combines warding off evil spirits and protecting the apple harvest with a good knees-up tonight at the National Trust properties, Barrington Court and Montacute House.

Forget pesticides, it's the wassail which makes Somerset's apples great – and with the trust staff you can help keep this ancient ritual alive.

Both estates will be open for an evening of loud singing, lively dancing and local theatre.

"It's all about noise," says Matthew Applegate, visitor services manager at Barrington Court.

"It's a celebration to scare off any evil spirits which may threaten the year's apple crop.

"As well as enjoying a glass or three of cider and apple juice, there's music from the Samba Band, poetry, a bonfire, the Langport Mummers and the evening is rounded off with gunshots fired into the orchards."

In the late 19th century, Barrington Court was closed up and in a sorry state. Canon Hardwicke Rawnsley, one of the founders of the National Trust, was taken around.

Despite its appearances, he recommended that the trust acquire it, which it did in 1907.

One hundred and two years later, staff and volunteers there are turning their hand to the production of cider.

A path was created south of the kitchen garden to link the court with the beagle kennels (now the visitors' reception).

It's along this path that Elsie Lyle designed and planted the herbaceous border in 1921. Opposite the border is the Goose Orchard, retained by Forbes and originally known as the Old Orchard in 1842 and now underplanted with daffodils. The orchard is the most important of the old cider orchards around the property and the geese that grazed there behind chestnut palings are still talked about (they left in 1990).

The word "wassail" comes from the Old English "waes hael" meaning "be well" or "be of good cheer".

It's believed to derive from a custom when, at the beginning of each year, the Saxon lord would shout "waes hael!", and in reply the assembled crowds would shout back "drinc hael", meaning "drink to be healthy".

No one knows the author, but an ancient poem sums up the event:

"Wassail! Wassail! all over the town,

Our toast it is white and our ale it is brown;

Our bowl it is made of the white maple tree;

With the wassailing bowl, we'll drink to thee."

"The need to protect our orchards from evil spirits may have passed," says Grahame Meaden, visitor services manager for Montacute house, "but this is a great chance to enjoy Montacute and Barrington Court after dark while also experiencing a good family-themed knees up in the bleakest part of winter.

"It's also a fantastic chance to learn about the National Trust's involvement with good local food and great local traditions."

Gates open at Barrington Court at 5pm. Last admission is at 8.30pm. Adult tickets cost £2.50 and admission for children under 18 is free. Dress for a night outside and please bring a torch. Visit www.nationaltrust.org.uk/barrington

In Barrington village, five miles north-east of Ilminster on the B3168. Signposted from A358 (Ilminster–Taunton) or A303 (Hayes End roundabout).

At Montacute House, meet in the car park at 6pm. Last admission is at 8.30pm. Adult tickets cost £2, £1 for children or a family ticket costs £5. Dress warmly and please bring a torch.

Visit www.nationaltrust.org.uk/montacutehouse