SWEET POTATO

Mercury (Hobart) - Magazine - - GROW YOUR OWN - WITH JEN­NIFER STACK­HOUSE

There are plenty of plants that don’t grow eas­ily in Tasmania but some of these are worth a try — es­pe­cially with the fore­cast of a hot sum­mer ahead. Lately I’ve seen plenty of mar­ginal plants for sale in­clud­ing all sorts of citrus and ba­nanas.

While ba­nanas are too big a com­mit­ment for me, I am will­ing to give sweet pota­toes a go after see­ing plants grow­ing well in a friend’s gar­den. That lush and pro­duc­tive vine was grow­ing in a raised veg­etable bed and although the crop was small it did pro­duce. Right now there are sweet potato plants for sale in gar­den cen­tres.

Pot­ted so­lu­tion

Nor­mally sweet potato (Ipo­moea batatas) likes to sprawl across the ground. It’s part of the morn­ing glory fam­ily (Con­volvu­laceae) with small white or pink morn­ing-glory-like flow­ers. The heart-shaped leaves are also pretty.

I’ve grown sweet pota­toes be­fore when I gar­dened in a warmer cli­mate but even there the vine was of­ten de­stroyed by frost be­fore the crop was ready to har­vest. I hit on a tech­nique then that worked well and I am now em­ploy­ing it here. I’ve bought a very big black pot (50cm across) and filled it up with sev­eral bags of premium pot­ting mix. In has gone the sweet potato plant, which was al­ready grow­ing well, sur­rounded by a com­fort­ing layer of mulch, and a tri­pod of stakes.

It is pos­si­ble to grow sweet potato from sprouted tu­bers but these ad­vanced plants give a head start and the black pot should help keep the plant warm. I’ve planted an or­ange va­ri­ety but they also come as white and pur­ple. Sweet pota­toes are some­times called yams and thought of as a trop­i­cal veg­etable from the Pa­cific Is­lands. Not so. Sweet pota­toes are na­tive to Cen­tral or South Amer­ica. They spread across the Pa­cific to New Zealand per­haps more than 1000 years ago. Sweet potato is of­ten called by the Maori name ku­mara.

When sweet potato is grown as a ground cover it forms tu­bers as it spreads and forms roots. In a pot or raised bed, either al­low the vine to sprawl over the edges or train it up a tri­pod at least 2m high. Don’t let it form roots into the soil. These tech­niques re­strict the num­ber of tu­bers but those that grow have a chance to ma­ture.

Cold is the en­emy of the sweet potato. Cold winds or a cold spell set the vine back while a frost or very low overnight tem­per­a­tures will kill above-ground parts. To give the sweet potato plant ev­ery chance to thrive, select the warm­est part of the gar­den for ex­am­ple against a north-fac­ing ma­sonry wall or at least be­side a shel­ter­ing fence so the sweet potato vine can grow for the nec­es­sary 16 to 25 weeks to form a crop. Mine is sit­ting on top of brick paving, which warms up dur­ing the day.

On­go­ing care

Whether they are in the ground or in a pot, keep the plants grow­ing well with reg­u­lar wa­ter­ing and en­sure they’re free of com­pet­ing weeds. Once they smother the ground their fo­liage tends to act as liv­ing mulch. Ex­cess leafy growth from sweet potato vines can be pulled up through sum­mer and au­tumn and fed to the chooks.

Ap­ply com­plete slow-re­lease fertiliser at plant­ing. An oc­ca­sional liq­uid feed­ing helps pot-grown plants keep grow­ing well.

Once the weather gets cold or frosty or the leaves start to yel­low, re­move the top growth and search for tu­bers. Take care if dig­ging as sweet potato tu­bers are eas­ily dam­aged. In a pot, har­vest­ing is as easy as tip­ping out the pot­ting mix, pick­ing up the tu­bers, brush­ing off the soil and head­ing for the kitchen.

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