Potato Group in Crop Rotation: Potatoes, Tomatoes and More

The potato group — technically the solanum or solanaceae family — is one of the most important groups to manage correctly in a vegetable garden rotation. These are hungry crops that demand the richest soil in the rotation, and they share susceptibility to blight, one of the most destructive diseases in the kitchen garden. Getting the potato group right sets up the entire rotation sequence for the year.

Which Crops Belong in the Potato Group

The potato group includes all potato varieties (first earlies, second earlies, and maincrops), tomatoes, peppers, chillies, aubergines, and physalis. All are members of the Solanaceae family. This family relationship is why growing tomatoes where potatoes grew last year is not a safe choice — they share the same diseases and you are effectively breaking your rotation. Even in a small greenhouse, tomatoes must move to a new position each year or the growing medium should be replaced entirely.

Why the Potato Bed Gets the Most Fertility

Potatoes are the heaviest feeders in the rotation. They need a deeply dug, richly manured bed to produce a worthwhile crop. In the classic four-year sequence, the potato bed receives the lion's share of well-rotted manure or compost — typically one to two barrowloads per square metre incorporated in autumn or at planting time in spring. This generosity is justified because the high organic matter helps retain moisture, suppresses weed germination between the rows, and provides sustained nutrition for the long growing season. The earthing-up process also improves soil structure, loosening compaction and creating the friable tilth that benefits the brassica group in the following year.

Blight and the Case for Rotation

Late blight (Phytophthora infestans) is the main reason rotation matters for potatoes and tomatoes. Blight spreads primarily through airborne spores during warm, humid conditions, so it can infect from nearby gardens regardless of your rotation. However, blighted potato debris left in the soil carries the pathogen over winter, and infected tubers left in the ground can become "volunteer" potato plants the following spring that act as a reservoir for re-infection. Moving the potato group each year and clearing all debris meticulously reduces the risk of soil-carried blight. Potato cyst nematode is another serious soil pest that rotation helps contain, as the nematodes decline significantly in the absence of a host crop.

Spacing and Earthing Up in Rotation Beds

Potatoes are planted in rows 60 to 75 centimetres apart, with plants spaced 30 to 40 centimetres apart within rows depending on the variety. The earthing-up process — drawing soil from between the rows up over the emerging stems two or three times during the season — serves multiple purposes: it covers developing tubers to prevent greening, smothers weeds, and progressively loosens the entire bed. By harvest time, the soil has been worked to a depth and looseness that few other cultivation methods achieve, which is why following potatoes with brassicas is such a productive pairing in the rotation.