When to plant sweet potatoes – whether growing outside or under cover

Find out exactly when to plant sweet potatoes and enjoy the many health benefits this crop offers. These extremely frost sensitive plants need about 90 to 170 days to fully mature and give the bumper crop you’re after, so it's important to plant them at the right time.

Boiled, fried, mashed or baked, sweet potatoes contain an abundance of fibre, beta-carotene and a far lower GI than regular white potatoes, making them the healthier choice for your dinner plate. 

Get the timing right, and once you know how to grow sweet potatoes, you can enjoy  many different varieties that you won't be able to find in the grocery store.

When to plant sweet potatoes

Sweet potato slips – the small shoots that grow out of the potato – need to be started indoors about six weeks before you are ready to plant them outdoors as part of your plans for when to plant vegetables. They are extremely frost sensitive, so cannot go outside until you are absolutely sure the last frost date for your area has passed. 

Check your USDA plant hardiness zone to see if they will fair well in your climate. If the temperatures in the area where you live are unpredictable, it might be advisable to grow sweet potatoes under cover in a polytunnel, or include them in the crops to grow when planning a greenhouse. 

'Sweet potato slips are best planted outdoors when the soil temperature is warm enough, above 65°F (18°C) advises Jacqueline Thorne from Highland Horticulture.

What month is best to plant sweet potatoes?

The best month to start sweet potatoes will depend on the climate where you live and the last frost date.

Spring is the best time of year to start sweet potatoes, but they must only be planted outdoors once all risk of frost has passed. 

'Sweet potatoes are sensitive to cold conditions, so gardeners need to wait about four weeks after their last frost date to plant them out,' advises Melody Rose from Dave's Garden.

Sweet potatoes take between 90-170 days to mature and will need warmth to grow well. For this reason, it might be advisable to grow them under a cover to ensure you get a good harvest. 

'Sweet potato slips need to be started about six weeks before you plant them out. Bury the sweet potatoes in moist sand, compost or leaf mulch,' advises Melody. Then, place them on a sunny windowsill and only plant them outdoors once all risk of frost has passed. 

Can I start sweet potatoes outdoors?

As sweet potatoes are warm loving plants, like pumpkins and zucchini, and very frost sensitive, you should only start them outdoors if you live in a warm region. You should check your USDA plant hardiness zone to see if they will do well in your area outdoors.

Soil temperature needs to be consistently about 65°F before you can start thinking about planting sweet potatoes outdoors. For many gardeners, therefore, it is advisable to start sweet potato slips indoors. 

When to plant sweet potatoes in a container 

Growing sweet potatoes in a container as part of your vegetable garden container ideas is a great option if you only have a small yard or outdoor space. It also ensures you manage to harvest the entire crop and not leave any potatoes behind.

'We recommend that sweet potato are best grown in a polytunnel or glasshouse or under a large cloche, irrespective of whether they are planted into containers or soil beds,' advises Iain Thorne from Highland Horticulture. 'When grown this way, planting can begin from early to mid spring, depending on location and last frost date,' he adds.

Next job: check when to harvest sweet potatoes.