Earth up container-grown potatoes to keep them growing on strongly for your earliest-ever crops. Potatoes form tubers along their roots underground, so the more root the plant grows, the bigger your harvest. Adding more compost as they grow also keeps tubers buried deep underground: if they form too close to the surface and light reaches them they'll turn green and inedible.
After you've planted your two or three seed potatoes and covered them with a few inches of compost it will be just a few weeks before sturdy green shoots are thrusting up above the surface. Once they're about 15cm high, if you're using potato bags roll up the sides a few inches before adding more compost.
Use a 50:50 mix of general multi-purpose compost and a nutrient-rich soil-based compost such as John Innes no. 3, and carefully bury the shoots in compost until just the top leaves are showing. Then repeat as the plants grow, earthing up every time the shoots grow another 15-20cm, and watering generously throughout. Keep them warm – a cool greenhouse or sunny spot on the patio is ideal – and you'll be tipping out your first crop of delicious new potatoes by the end of next month.
