Sweet potato slips from whole tubers

Lay whole sweet potatoes on their sides in loose soil under a layer of straw, a hand apart, and cover them about halfway. Keep the bed damp and warm; a sunny spot against a wall works. Nothing shows for a few weeks, then sprouts push up through the straw. Any grocery sweet potato will do, and a mix of varieties gives a mix of colours at harvest.

When the sprouts are a hand tall with a few leaves, lift the tuber. Each sprout is a slip: hold it at the base and twist it off. A tuber gives a handful of slips at a time and keeps producing if you re-bed it, so pull in rounds rather than all at once.

Stand the slips in glasses of water on a sunny sill, bottom third submerged and leaves clear of the water. White roots show within days and fill the glass in a week or two; change the water every few days. Plant out when the roots are a finger long and the soil is warm, a foot apart. The vines cover the bed by midsummer.