Dahlias at Rousham Garden: seventy years in the growing Few and far between: a spiky sea urchin type The remarkable thing about the Rousham dahlia bed is not just its scale, but also that it has survived in the same place now for 70 years. In other country house walled gardens, as dahlias fell from fashion they were replaced by permanent herbaceous perennial beds, but here dahlia continuity has gone unbroken. The garden at Rousham is open every day of the year and the dahlia bed is brilliant for keeping the walled garden interesting late into autumn. It's earned its keep, so it has stayed. The same nearly 500 tubers have been lifted and stored in the cavernous cellar below the main house every winter. One may think that it's a bad idea to plant the same thing in a border for five years let alone 70, but with dahlias this is obviously not the case. The odd new variety has been added, but in the main, the colour and forms have remained the same. Colour splash: there are flashes of scarlet Ann says she's noticed that mauve seems to be the dominant colour now, which has not always been the case, and assumes some tubers have reverted, but in among the mauves, there are also splashes of scarlet and yellow and the odd apricot and orange, with a regularly repeated, jazzy red and white bi-colour form. Lots of the dahlia types come from the Decorative group and a few from the Waterlily group, with their classic broad petals. There are fewer spiky cactus, sea urchin types, but a handsome white form, with a green eye, pops up regularly. None of the names are known, they've just been there too long. If we get a few more sunny autumn days and you feel like a garden visit, Rousham should be at the top of your list. Rousham Garden, Steeple Aston, Oxfordshire, is open every day, including Christmas day, 10am-4.30pm. Entry £5 (rousham.org) See sarahraven.com for a good selection of dahlias by mail order The dahlia year At Rousham, dahlias are lifted once frost has blackened the stems - usually in mid-November. Each plant is cut down, with a couple of inches of stem left on the roots (right). Plants are labelled - with row and position in the bed - and crated. They are then all taken down to the cellar, the soil left on. The tubers are just left to dry out as they are, not turned upside down, and stored just above freezing until May. Replanting The tubers are replanted in the same position at the end of spring. The Rousham gardeners don't bother to bring them into growth by planting in the greenhouse early, they just plant them out straight from dry. If a tuber gets too huge, it will be divided at this stage, just before planting. At least one stem must be attached to each section before it is separated from the mother clump. This is done with a sharp spade. Soil preparation The reason for lifting the dahlias is so that the gardeners can then condition the bed for replanting. The whole area is dug over, with tons of farmyard manure added. Dahlias love their soil rich and well-drained, but also moist - the manure helps with water retention too. Watering Dahlias love lots of water - which is why they have been so stupendous this year. They have been very late to flower and the slugs did terrible damage early in the summer when it did nothing but rain, but many people are reporting dahlias towering above them this season. For this reason, at Rousham, after replanting, a leaky pipe is laid out over the whole bed, spaced at 18-inch intervals, and - depending on the rainfall - is turned on for a couple of days every 10 days or so. This guarantees the soil is moist and encourages huge, healthy plants. Staking In June and July, when growth really takes off, every plant is staked. The gardeners use a mix of bamboo canes and string, with sturdy, metal hoops for the larger and heavier varieties. The site is very sheltered, but such is the massive, lush growth of dahlias that without support, whole limbs of the plants will break off under their own weight.