Use cold-stored potato tubers, available from specialist seed merchants in July and August. These are seed potatoes from late winter that have been held back ready for summer planting.

First and second early varieties such as ‘Charlotte’, ‘Nicola’ and ‘Maris Peer’ are recommended. As these will go straight into warm soil, they do not need to be chitted prior to planting.

You can hold back late-winter-bought tubers yourself by keeping them in the fridge or leaving them in a cool, light place right through the spring and early summer and allowing them to develop long (and rather fragile) sprouts. These will need to checked regularly for aphids.

Potatoes harvested in summer and then replanted will not produce

Tubers are swollen, usually underground, parts of a stem or root used to store food by the plant. They have buds that can produce new plants. Examples are tuberous begonia, cyclamen, dahlia and potato.

Dormancy refers to a period of inactivity in plants, during which they slow down or stop their growth, conserving energy and resources. This is a natural process that helps them survive harsh conditions, such as winter or drought. Dormancy in seeds is a mechanism that prevents them germinating until environmental conditions are favourable for growth.

dormancy

Most early potatoes take about 12 weeks from planting to cropping.

Potatoes planted outside in the ground in midsummer should grow and form tubers before the first frosts in autumn, especially in sheltered gardens in the south.

Where there is a frost free-greenhouse, cool conservatory or bright porch, potatoes can be planted in late August/early September for harvesting at Christmas.

1. Use a container at least 30cm (1ft) deep and wide, with drainage holes in the base (specialist potato-growing containers are also available).
2. Add a layer of potting compost or garden soil mixed with garden compost or well-rotted manure. A layer 10cm (4in) thick is sufficient for 30cm (1ft) deep pots, but larger containers can be half-filled.
3. Plant one to three tubers per pot, each with about 30cm (1ft) of space, and cover with 15cm (6in) of compost or soil.
4. As the foliage develops, earth up the potatoes with further compost or soil until the container is full to within 5cm (2in) of the top. Leave a lip to aid watering.
5. Keep well-watered and feed with a general-purpose liquid fertiliser.
6. Ensure the greenhouse remains frost-free as the season progresses, as potato foliage would be damaged by frost.
7. The foliage will yellow and die down in late autumn and can then be removed and composted.
8. Tubers can be left in their pots in compost (kept fairly dry) until needed at Christmas.

How to grow potatoes outdoors for Christmas harvests

1. Follow instructions for growing potatoes, including planting them in a trench and earthing them up as they begin to grow.
2. Take measures to protect against potato blight and slugs.
3. Once foliage dies down in September or October, remove and compost it.
4. On light soils in a sheltered garden, piling some earth up over the row where you know the potatoes are and covering it with straw to insulate tubers may be sufficient protection to store them in the ground until Christmas.
5. In cold areas, or where soils are wet and heavy, it is better to lift tubers by the end of October and re-bury them in coarse sand or soil in a frost-free place (such as a garden shed) until you need them.
6. Lifting and storing potatoes in the fridge, or in bags in a cool shed, is possible but will cause the skins to harden and the desirable, delicate ‘new-potato’ flavour and texture will be lost.

Home-saved tubers can suffer from pest, disease and dormancy problems, so try to buy tubers intended for summer growing. Other problems include:

• It can be costly to heat a greenhouse efficiently
• Potatoes are prone to scab and a number of rots but this can usually be avoided when they are grown in fresh compost in containers
• Slugs and snails can damage foliage, stems and tubers underground
• Potatoes grown outside in summer and autumn are especially prone to potato blight. Those in containers indoors are not usually at risk
• Keep an eye on the weather forecasts as early frosts will blacken foliage and weaken plants; fleece protection may be needed for outdoor crops