- Tuberous border dahlias are easy to propagate from cuttings. To do this, you should start them off now. Pot up the tubers into large boxes (or individually into 6in containers) filled with moist potting compost and place in a warm, well-lit greenhouse or conservatory. Young shoots will soon emerge, and some of these can be used as cuttings when they are about 3in long. Dahlia cuttings should be left to form roots (in pots) under cover, then planted outside in late May or early June. A sheltered, sunny spot and welldrained soil are essential.

- If you have autumn-fruiting raspberries such as ‘Autumn Bliss’ or ‘All Gold’ growing, they need to be pruned in the next couple of weeks. This will allow new fruit-producing canes to emerge and provide this year’s crop. Cut all the old canes to 1in above ground level, remove any perennial weeds from the surrounding area and spread a mulch of well-rotted compost around the crowns. The unwanted woody material should be chopped up and placed on the compost heap.

- Jerusalem artichokes can be planted outside this month, as long as the ground is not frozen or waterlogged. Choose a smooth-skinned, easy-to-peel variety such as ‘Fuseau’ (available from www.thompson-morgan.com) and bury the tubers 4in-6in deep and 15in apart. They thrive in sun or semi-shade and any welldrained soil. The stems can grow up to 6ft tall, so bear this in mind when cultivating them near other crops, as they may cast a lot of shade. The artichokes will be ready for harvesting in the late autumn.

- In my herbaceous border, new shoots are appearing at the base of many of the plants, including erigerons, nepetas, rudbeckias, sedums and stachys. To make room for these, I remove last year’s stems, which were left in place during winter as a source of food and shelter for insects and birds. To ensure that garden wildlife has the best chance of survival, I always resist the temptation to cut them down too early – the end of the month or early March is an ideal time.

Your questions answered

When should I remove unruly stems from my deciduous berberis?

K McFarland, Nottingham

This slow-growing shrub can reach heights of up to 6ft, with a similar-sized spread. It does not need to be pruned annually, but any unwanted stems are best cut back or removed in late winter.

Which leek varieties are suitable for growing and overwintering outside?

H Noble, Shipton

There are generally three types of leek: early-season, mid-season and late-season.

Mid- and late-season varieties produce short, fat stems and can be left in the open ground, then lifted as required through the winter months. The most reliable varieties include ‘Musselburgh’, ‘Giant Winter’ and ‘St Victor’. If you want to grow any of these leeks, the seeds should be sown outdoors in March and April.

Neil Wormald is a qualified horticulturalist. Send your questions to Garden Expert, Home, The Sunday Times, 1 Pennington Street, London E98 1ST, or e-mail garden.expert@ sunday-times.co.uk

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