They prefer rich soil, so dig in lots of well-rotted manure or compost, ideally the winter before planting. Space plants 3ft (90cm) apart and mark with a short cane so you can see where to water. Be mindful that young plants are a magnet for slugs and snails.
Water plants well, feed regularly with a high potash liquid fertiliser and mulch to retain moisture. Allow fruits to ripen in the sunshine for as long as possible, but harvest them before the first hard frosts, cutting the stem 4in (10cm) above the fruit. Don’t be tempted to carry the fruit by the stem as, if it snaps off, rot will set in. Kept in a cool, dry, well-ventilated spot, winter squash should last for several months.
Each year, Bertelsen experiments with different varieties. Among his current favourites for flavour are Jarrahdale, Burgess buttercup squash and ‘Rouge vif d’Etampes’. Organic vegetable grower and no-dig guru Charles Dowding’s two favourites are ‘Uchiki Kuri’ and ‘Crown Prince’.
He recommends ‘Uchiki Kuri’ for places with cooler summers as they ripen quickly. “The flavour is as good as butternut, and they are a lot easier to grow,” he says. He also recommends ‘Marina di Chioggia’ for its outstanding flavour.