Polymnia edulis

• Yacon Strawberry

Seed - sow mid winter in a warm greenhouse and only just cover the seed^[1]. Prick out the seedlings into individual pots as soon as they are large enough to handle and plant them out after the last expected frosts. Consider giving them some protection such as a cloche until they are growing away well. Plants do not usually produce flowers in Britain and therefore seed has to be obtained from other countries[K].

Division in autumn. The plant forms 2 distinct types of tuber. Large tubers, usually on thin roots 2 - 5cm long, are used as storage organs and do not have the capacity to form new shoots. These are the tubers that are usually eaten. Smaller tubers are formed in a cluster around the stem. These form the shoots for the following year's growth and so are the ones that should be stored. Dig up the plants in the autumn once the top growth has been cut down by frost. Remove the large tubers for food, cut the main stems back to about 10cm long and store these stems with their cluster of small tubers in a cool frost-free place. Do not let them dry out. Pot them up in early spring in a greenhouse. When they come into active growth divide each cluster into individual shoots with their tubers attached and repot these. Plant them out in late spring after the last expected frosts[K].

Cuttings of basal shoots in early spring in a warm greenhouse^[1]. Harvest the shoots with plenty of underground stem when they are about 8 - 10cm above the ground. Pot them up into individual pots and keep them in light shade in a cold frame or greenhouse until they are rooting well. Plant them out in the summer.

For best results, this plant requires a warm position in a deep rich soil^[1], though it survives even when growing in poor soils^[6]. Plants are fast-growing^[6]. In S. America, they succeed in areas with annual rainfall varying from 900 - 3500mm^[6], though are likely to succeed with less rain in temperate zones.

The yacon is cultivated for its edible tuber in the Andes, and is sometimes used in sub-tropical summer bedding schemes in Britain, though it is not very hardy^[1]. The top growth is killed back by frost but the tubers can tolerate at least light frosts^[6]. Plants are unaffected by day-length and so can produce good yields of roots in temperate zones^[6]. One report says that plants take 6 - 7 months to produce a crop from planting out^[6], though on our Cornwall trial ground they have cropped quite well with a 5 month growing period[K]. The roots are brittle and must be harvested with care to avoid damage^[6]. Yields of 38 tonnes per hectare have been recorded in South America^[6], whilst yields of over 2 kilos per plant have been achieved outdoors in Cornwall[K]. The harvested roots can be stored for several months^[6]. Plants have not been selected for flavour or yield, some roots can be exceedingly sweet whilst others are fairly bland^[6].

Plants might be useful in agroforestry because they succeed under trees^[6], though in the relatively sunless climes of Britain the plants are not likely to do well in the shade of trees[K].