Growing sweet potatoes: 10 tips for successful harvest

How to grow sweet potatoes at home? Here are the best sweet potato varieties, plus tips on planting, fertilising and harvesting – all about growing sweet potatoes.

Sweet potatoes (Ipomea batata) arrived in Europe already in the 16th century, even before the regular potato. However, while potatoes became a hit, sweet potatoes remained an exotic and hard to grow vegetable for most people. Within a short time, potatoes became the most important source of food in many parts of Europe. After that, the cultivation of sweet potatoes was not pursued any further, which is a shame. Although the sweet potato comes from the tropical and subtropical regions of South America, some cultivation tricks and adapted varieties make it possible to grow them even in temperate climate. In recent years, sweet potatoes have become more and more popular both in the kitchen and in the garden. A few years ago, the Weihenstephan-Triesdorf University of Applied Sciences in Germany undertook field trials to test the adaptability of sweet potatoes. The results show that sweet potatoes can thrive splendidly in moderate climatic conditions. This means that you too can grow and harvest your own sweet potatoes in the next gardening season in the comfort of your own garden. We have created an ultimate sweet potato cultivation guide exactly for this reason.

1. Tip: Suitable sweet potato varieties

With approximately 7000 sweet potato varieties, there is a huge diversity to choose from. There are types of sweet potato with red, yellow or white skin. The colouring of the flesh ranges from orange to white or purple. Similarly, the foliage is not always just green. Some cultivars have ornamental value because their leaves bear striking colours. Of course, other characteristics also play a significant role. Length of cultivation period is particularly relevant to those who want to grow sweet potatoes in their own gardens. Bonita, Evangelina or Beauregard all of which are characterised by a short cultivation period and reliable yields have proven to stand temperate climate.

2. Tip: The right location for sweet potatoes

The right location is one of the critical factors in sweet potato cultivation. For the tubers to develop well, a loose, sandy soil is a must – too many obstructions in the ground such as stones or very firm soil, will cause deformations on the delicious tubers and they will turn out smaller. Also, in dense soils, waterlogging is more likely to occur, which the plant does not tolerate well. Being a heavy grower, sweet potato likes nutrient-rich and humus-rich soils (this will reduce its need for fertiliser). At the same time, it is particularly heat-loving and sensitive to cold, which is why a sheltered, full-sun location is ideal. Those who cannot offer a sheltered location in the garden bed can also grow them in a greenhouse – protected from harmful weather influences, sweet potatoes thrive even in colder regions.

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3. Tip: Propagating sweet potatoes

Unlike the potato (Solanum tuberosum), for example, the sweet potato is very difficult to propagate by seed, as these germinate poorly. Rather try to let seed tubers or tubers from the previous harvest pre-sprout in the house and plant them in the ground later. For germination, set the sweet potato up to half in water and place on a bright window sill. To prevent the tuber from completely slipping into the glass of water, you can poke toothpicks into the sweet potato (similar to sprouting an avocado pit) and hang it in place. Once sufficiently long shoots of about 20 to 30 cm have formed, the tuber is ready for planting outside in the bed.

4. Tip: Growing sweet potatoes in garden bed

As sweet potatoes are sensitive to cold, you should not plant them out before the Ice Saints, when frost may still occur. If temperatures continue to fall below 10 degrees at night, you might even want to delay planting them even longer. Otherwise, the cold shock could stall the growth of the plants for a longer period of time. You can either plant the entire tuber or just the individual shoot cuttings that have formed during pre-sprouting. When planting the whole tuber, make sure half of it still sticks out of the soil. Similar to potatoes, sweet potatoes are worth growing with the row and hill method. Rows should be about 60 cm wide and 20 cm high. Growing hills will allow the soil to warm up faster, which promotes higher growth. At the same time, excess water can drain away more quickly and the risk of waterlogging is reduced.

5. Tip: Growing sweet potatoes in pots

Of course, sweet potatoes can just as well be cultivated in a pot – this option is especially suitable for colder regions as the pots can stay inside as long as necessary and move outside when the weather is warm enough. It is important for the pot to hold at least 20 litres of soil so that there is enough space. Using a black pot is a further benefit, as it does not reflect sunlight and the soil in the pot is thus warmed more quickly. Follow the same location requirements as for sweet potatoes in garden beds: make sure the substrate is loose and permeable, and provide the sweet potato with plenty of sun and a sheltered location.

6. Tip: Mulching and mixed cultivation

Especially during the first period sweet potatoes grow very slowly. As a result, the surface of the bed remains bare soil for a long time, which can lead to increased soil erosion. There are two common methods to prevent erosion. One is to cover the entire bed with black foil so that only the sweet potatoes peek out. This method, in addition to protecting the soil, has the advantage that the soil around the sweet potatoes warms up more quickly, thus increasing growth. Another advantage is that possible weeds are suppressed by depriving them of the necessary light. Of course, organic materials such as straw or leaves are also suitable for mulching sweet potatoes. On the other hand, you can also plant the sweet potato as a mixed crop: lettuce, radishes (Raphanus sativus var. sativus) or spinach (Spinacia oleracea) are particularly suitable because of their short cultivation time and you harvest them just in time for the sweet potato to have all the space in the bed for itself.

7. Tip: Watering sweet potatoes

Watering sweet potatoes basically follows the rule: The more leaves have developed, the more water the plant needs. While the young plants hardly need watering, the large plants have a very high water consumption in summer. In fact, with high temperatures and no rain, you should water them on a daily basis. Although sweet potatoes can usually survive dry periods well, the growth of their tubers suffers. However, too much water will also harm them, after all, it can be very sensitive to waterlogging. Also note that sweet potatoes grown by the hill method or in pots require more water – water evaporates much faster in dams and pots.

8. Tip: Fertilising

Since sweet potatoes are heavy eaters, many think that they need a large amount of fertiliser. In fact if you prepare the bed well at the beginning they do not require additional fertiliser throughout the growing season. To ensure optimal supply with nutrients, thoroughly work in about 3 litres of mature compost and 100 grams of horn meal per m2 – this will save you tiresome fertilising work later. When growing in tubs, unfortunately, a single fertilisation is not enough. Instead, apply some liquid fertiliser about once a week starting at the leaf growth phase.

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9. Tip: Sweet potato harvesting

The sweet potato does not start to form tubers until September. Therefore, its tubers are usually ripe for harvesting at the end of fall, i.e. in October. Fortunately, the perfect time to harvest sweet potatoes is easy to determine: As soon as the leaves turn yellow, the tubers in the ground are also ripe. Sometimes, however, weather may ruin the works if the first night frosts appear before the leaves turn yellow. In that case be quick as sweet potatoes do not tolerate cold. But don’t worry: even with an early harvest, the tubers are usually very tasty. In order to enjoy your sweet potatoes for a long time make sure to not damage the thin rind when harvesting, otherwise the risk of rot increases during storage.

10. Tip: Curing potatoes

Don’t worry: “Curing” is neither a new trendy sport nor a complicated sweet potato dish. It is a treatment to apply after harvest as self-grown sweet potatoes are usually significantly less sweet than you are used to from the supermarket because they contain more starch and less sugar. To ensure that the sweet potato still lives up to its name and is also easier to store, you can easily treat it at home: simply wrap the tubers with black foil, place them in full sun during the day and in the warmest room at night. The warm and humid climate inside the foil closes the small wounds in the skin and starch transforms into sugar inside the tuber. The result: After about five days, the sweet potato is significantly sweeter and can also be stored better.