In this series of monthly articles Bob explores the incredible range of plants you can grow in a greenhouse, conservatory or plastic tunnel. Not just the purely decorative but the scented and edible also, and maybe those plants that are just downright interesting. This month Bob nominates ~ Sweet potatoes.
Now here is a plant that is mis-understood and thus relatively neglected. Few other indoor climbers offer such clean, shiny, pest and disease resistant and decorative foliage with such pretty pink and purple flowers. And that is to almost ignore the huge crop of tasty tubers they also produce. There are two main strains. The yellow fleshed red and purple skinned ones which are hard, dry and easiest to crop. And the more challenging and more worthwhile moister, orange fleshed orange skinned sorts such as Jewel. Slips of several varieties are sold commercially though arriving a bit late in the season so alternatively buy a suitable, preferably organic (no anti-sprouting chemical used!) shop sweet potato early in the New Year. Scrub, and pot this in gritty compost placed over gentle heat.
Shoots will sprout and when these are finger length carefully detach them, pot up separately and treat like tomato or pepper seedlings. (If you plant the tuber as with a potato set the flesh rots and often takes the shoots with it.) Grow the young plants on in any good potting compost moving them up to bigger pots regularly and do not stint on the watering for these are thirsty plants. Train the foliage up canes or strings and never allow the stems to touch the soil as they root there and waste energy producing loads of tiny roots. You will have magnificent plants flowering all the summer and autumn. These could go outdoors from mid May but crop poorly in the open ground and the tuberswill probably suffer from horrific pest damage. Fortunately they look better, live longer and crop heavier when kept under cover. Unless they are kept exceptionally bright and warm their foliage dies back in winter when the pots should be dried off.
Then the roots can be turned out as required. Small tubers are eatable from mid-summer but given a long season the crop can be huge if grown well in big tubs. They do not store well so use them as soon as evicted though if heat treated with gentle baking they can keep longer. Indeed they keep best if simply left in tubs of dried out compost. And if you find you don’t like sweet potatoes then you can still grow them and eat the leaves as a spinach!