Rising stars of the underground scene
There is a lot to be said for having a little part of your world that doesn’t remind you of your failings. As a man in his 40s, I wake up some mornings thinking I’m in jail before remembering that eyebrows now grow that quickly. In the veg patch, it is little better: the brassicas look at me sideways through cabbage white season, the summer salads remind me that the slugs like their five-a-day too, and the tomatoes are always happy to accommodate passing aphids.
Underground crops offer blessed relief. Their aboveground growth is relatively encouraging to behold, often beautiful, and the potential prize (and any associated worries) is hidden away, giving the impression that all is well. It’s a splendid state of affairs: this is one part of the veg patch that doesn’t make me feel anxious, and getting it going starts in the next weeks. While I’m busy sowing the early spring veg under cover, I’m looking for dry spells to plant a few tubers outside in the hope of a fine haul later in the year.
Sweet potatoes ( Ipomoea batatas) did well in last year’s long, warm summer and, now my family has quite the taste for them, I’m charged with growing plenty more. Sweet potatoes belong to the Ipomoea genus, along with flowering climber morning glory, with which they share trumpet flowers and that characteristic rambling habit.
Sweet potatoes in the shops are orange, but home-grown varieties span orange to purple. They are increasingly popular as a low-carb alternative to potatoes, but they’re not just a worthy spud; they roast, bake and take to a gratin superbly.
Perhaps the most risky of the tubers, sweet potatoes need warmth. However, new varieties have been bred to make a go of things even in our unreliable climate. My favourites are ‘Evangeline’, a very sweet, orange- fleshed variety; ‘Beauregard’, highly productive with medium-sized orangefleshed tubers; and ‘Murasaki’, purpled skinned with dry, white flesh, cropping a week or two later than ‘Beauregard’.
Give them the sunniest spot you can. Unlike mashua (see below), sweet potatoes won’t climb even if given a supporting structure and offered whisky macs at each base camp: their foliage will trail and scramble for 3ft-6ft (1m-2m), which smothers out neighbouring weeds.
Sweet potatoes are traditionally started from unrooted cuttings – shoots that have been removed from chitted sweet potatoes – known as slips. You may source them now to pot yourself, or buy 9cm/3.5in potted plants for delivery in a couple of months’ time when the frosts have passed. If they arrive naked, as it were, soak each slip in water, then pot up to the first leaves and place in either an unheated propagator or cover the pot in a clear plastic bag until they’ve rooted. Plant out (12in/30cm between each plant, in rows 28in/70cm apart) after the last frosts, in the sunniest spot you have or, better still, in a greenhouse or polytunnel.
If you are growing them outside, warm the ground with black plastic for a couple of weeks. You can plant through the plastic to give them a boost, and a little fleece covering will get them off to a good start. Sweet potatoes will do well in large containers, but you should feed them regularly.
As a rule, sweet potatoes are pest-free – your gamble is with the climate. A good summer means plenty of potatoes, even outside. The tubers are ready when the foliage yellows in early autumn. Leave them in the ground for as long as possible to swell the tubers, but dig up before the frosts arrive.
Allow any for storing to dry and cure in a greenhouse, polytunnel or on a windowsill for about 10 days. Store somewhere cool and dry.
Mashua ( Tropaeolum tuberosum) was last year’s great success. As with potatoes, mashua hails
Sweet potato soup
This is so simple and the smokiness of the chipotle chilli keeps the sweet potato from any danger of being too sweet. 5 shallots Oil and butter 5 large sweet potatoes, peeled and diced 4 garlic cloves, finely chopped An inch of chipotle chilli Handful of thyme leaves 450ml chicken stock Good splash of milk Olive oil Ground paprika Salt and pepper
Finely chop the shallots and fry them very gently over a lowmedium heat in a good knob of butter and olive oil for a couple of minutes. Add the sweet potato to the shallots, cooking until they just start to soften. Add garlic and cook for a couple of minutes. Add chilli, thyme and stock and simmer until the sweet potato is tender.
Zap in a blender until completely smooth. Return to the pan, taste and add a little milk – I tend to add 100ml or so, but it depends on the texture of the sweet potato. Stir, warm through, and serve with a Zorro of olive oil, a dusting of paprika and plenty of salt and pepper. good – a little like capers, and especially good pickled.
They can be grown in a wellwatered and fed container, or planted – 16in (40cm) between them – in a sunny but moist spot. It is a herbaceous climber that will make a good few metres in height if it has a scaffold and space to scramble.
I’d not be without Jerusalem artichokes ( Helianthus tuberosus). Their knobbly tubers are one of my favourite winter, or any other season, ingredients. With an earthy, mushroomy taste, they are versatile, making a wonderful soup (use instead of sweet potatoes in the recipe, left) or a splendid base for risotto. They are also superb roasted (scrub, cut into chunks, toss in olive oil, salt and pepper, and roast for 30- 40 minutes at 190C/375F/gas mark 5, or roast whole for a little longer). Rather than crisp up as a potato might, they semi-collapse and soak up flavours, making them a fine partner to other veg as well as beef and lamb.
They couldn’t be easier to grow – just sink each tuber (6in) 15cm into the soil, 20in (50cm) or so from its neighbour, and come back in winter. They are perennial, but unlike many perennial tubers they don’t need lifting and replanting the following spring.
I have a patch in an orchard that started from a few dozen tubers about five years ago: I do nothing except take my fork to it every winter, lifting tubers as I want them. ‘Fuse’ is the variety to go for: all taste the same, but this is the least knobbly variety, which makes for easy peeling.
The tubers develop late, as winter sets in, and will happily stay unharvested, whatever the weather. Lift as you need them, as they don’t store for long.
Once you get into buried treasure, it can become quite obsessive – I similarly love oca, Chinese artichokes, yacon and groundnut to name but a few – so be prepared: you’ll find new ones to try every year.
Buy six ‘Beauregard Improved’ sweet potato premium plug plants for £14.99 and get six ‘Carolina Ruby’ premium plugs free. Call 0844 573 6015 (quote TET76) or visit gardenshop.telegraph.co.uk/offers. Contract with Thompson & Morgan. Offer subject to availability.
Buried treasures: clockwise from main, sweet potatoes are an increasingly popular low-carb alternative to potatoes; planted in a warm, sunny position they have a scrambling habit; mashua tubers have a peppery taste, with hints of aniseed and basil;...