Vegetable Garden Basics: How to Grow Sweet Potatoes

Sweet potatoes are a wonderful source of Vitamins A, E and C, as well as fibre, and are actually a member of the convolvuli (morning glory) family and not at all related to the ordinary potato.  They have a rich indulgent taste and have no cholesterol or fat.  Great with a roast, cold in a salad, or as a soup base, they provide good variety, colour and taste in a number of dishes.  Growing sweet potatoes is not difficult if you have space, although they are not always trouble free.

Preparation

Sweet potatoes like a free draining, organic-matter-rich soil which can be slightly acid (between 5 and 6.5). Although they do like some fertiliser, avoid using a product that is too high in nitrogen or you will grow leaves at the expense of the tubers.  Sand is the best soil type, and sand with the addition of mature compost is ideal.  You may struggle with clay so perhaps mix some sandy material in with the clay and dig more deeply.  Another option is to heap the mounds a little higher, above the clay base.

Location

They are sun lovers and prefer a semi tropical climate with at least 4-6 months of frost free growing.  You can grow in cooler climates but you have to take precautions with frost.  They do need space so be prepared to let them ramble.

Planting

Sweet potatoes are best grown from cuttings or slips, which can be planted in seed bed rows about 15cm (6″) high, and 30-40cm (12-15″) apart.   The cuttings need to be stripped of all leaves except the top tips and plant about 5-7cm of the cutting into the soil. Although best planted at the end of winter, some plastic sheeting across the top of the bed will assist in promoting soil warmth.  Harvest time will be from late summer.  Progressive planting is best as they don’t store particularly well, and perhaps plant a few cutting s every 2 weeks.  They just take a little longer to mature as the weather cools again.
If you have lots of space and aren’t after a neat look then plant lots and let them have their way.  Sweet Potatoes are fairly self- sufficient as they don’t need a lot of water or food once established, and love to flourish and spread.  As for food, avoid any nitrogen rich options and go for compost which can provide potassium and phosphorus as root vegetables love these.
If you lack the space you can still grow sweet potatoes in containers.  They may end up a bit small, but they ought not to be ruled out just because of this.   It is also possible to propagate by using, yes, you guessed it, a sweet potato, and there is a great post about this to be found at The Journey to Simple.

Growing Problems

Weevils are the main enemy here as they will eat the roots, the tubers and the leaves so can be a major concern. As well as weevils there are lots of bugs that love to feast on the leaves, but these are less serious. Sweet potatoes can also be affected by  fungus and blight. The latter can be mitigated by raising the seed beds to provide better drainage, and the leafy bugs can be kept at bay with an organic solution such as soapy water, chilli or garlic spray.
Also to  help avoid fungus try sprinkling a bit of corn meal on the ground, or a brew of baking soda diluted with water.  This effectively changes the pH of the plant slightly with the idea of making it uncomfortable to the fungus.  Bordeaux spray is often recommended but this contains copper, however chamomile spray can also be useful.  This is just a teabag based brew, which is an interesting solution.  A variety of organic techniques is a good balanced approach.
As for the weevils, there are lots of nasty chemicals available, however these don’t guarantee a weevil free crop and it seems the best prevention is to destroy plants as you notice weevil activity or distorted growth in the crop.  There are pheromone based sex traps that can help, but keeping the ground surface free of weeds, using good organic compost to keep them growing strongly, and some companion planting may assist.  The best companion plants for sweet potatoes are aromatic herbs such as dill, thyme and oregano.  Summer savory is also reported as being beneficial.  Crop rotation is a must so you will need to find a fresh planting space annually to minimise this problem.
As in all things garden, speak to your local nursery who can advise more resistant types.  After all there is not much to gain trying to grow a variety that is known to perform poorly in your area. Resistant strains of vegetables generally produce far more satisfying results, so my advice is not to fight it, and go for what works! After all you want to be enjoying the process not fighting it!

Harvesting

Your sweet potato crop should be ready anywhere from 14 to 20 weeks after planting.  The only good way to see if they are ready is to have a look!  Gently wriggle around with a garden fork and if they have grown well there should be several roots ready for you to snip off.
Once dug out of the ground leave them in the sun to dry for a while.  They are best left to cure (heal) for a week or so although you can eat them straight away if you prefer.  Some professionals leave them in the ground to store as they don’t keep very long out of the ground.   Like potatoes they are best kept in a cool place.

Varieties and Nutrition

According to the International Potato Centre (who would have thought there would be such a place!) there are apparently 6,500 different varieties of sweet potato.  In Australia typically, there are a few different colours of sweet potatoes available, which are also known as yams or kumara. These range from orange to red to white and purple white.  The most popular American and Australia varieties are Beauregard or Jewell, which are the longer red coloured variety.
Some people favour the leaves as well which can be used a little like spinach.