Potatoes require an open, frost-free site with deep, fertile, moisture-retentive, friable soil, for high quality and heavy yields. Improve soils by adding organic matter, such as well-rotted manure, in the autumn. Before planting, supplement with a general fertilizer, such as Growmore or blood, fish and bone, applied to the soil surface or spread along the sides of the drill during sowing, at the rate of 1kg per 10m (2.2lb per 33ft) row. Half of this amount will be enough if the garden is known to be fertile.
Once chitted (see propagation section below), seed tubers can be planted in a drill or individual holes and earthed up as they grow.
Plant early potatoes in early April, with later cultivars being planted mid-April. In northerly districts and during adverse weather little loss results from delaying planting up to mid-May. Potato ‘seed’ tubers are also offered in late summer for a winter or Christmas crop and these can be productive in greenhouses, but planted outdoors they are vulnerable to blight disease and frost.
Potatoes can be successfully grown in containers.
To grow outside, carry out the following steps:
- Draw a drill 7.5-15cm (3-6in) deep with a hoe or spade
- Place tubers with the chits (sprouts) uppermost in the drill. Early cultivars should be spaced 30cm (1ft) apart in the row and 60cm (2ft) between rows. Later cultivars should be spaced 35cm (14in) apart and have 70cm (28in) between rows
- Push the soil gently back over the tubers, ensuring that they are covered with at least 2.5cm (1in) of soil
- Lightly rake over the soil surface to level it and mark the drill
- Earth-up the plants by drawing soil around the stems to form a ridge. The final height of the ridges should be 20-30cm (8in -1ft). Earthing-up will exclude light from tubers preventing them from going green – green tubers are potentially harmful if consumed
- Alternatively, black plastic mulch can be laid before or immediately after planting and this excludes light and suppresses weeds, so earthing up is not required. Remember to cut a slit or cross in the plastic at each planting hole to allow the foliage to grow through
- Protect the young growth from late frosts, either by drawing a little soil over them with a hoe or covering them with horticultural fleece
- Some hoeing might be needed to kill weeds, but earthing-up leads to the destruction of weeds and few will penetrate the foliage once it has covered the rows
- Removal of flowers is not thought to increase yield significantly, but watering boosts yields in dry spells, especially during the critical period when tubers are forming in early summer. Thoroughly soaking potatoes every 10 days at this period ensures numerous tubers are initiated and also helps to prevent common scab disease. Watering in late summer may help crops bulks up and avoid second growth (see Problems below)