When to harvest sweet potatoes – and enjoy a healthy and plentiful crop

It's an increasingly popular crop to grow at home, but knowing when to harvest sweet potatoes can still be something of a mystery. 

Grown from ‘slips’ – unrooted cutting off existing plants – these warmth seeking plants are fairly fast-growing and send out lengthy trailing vines, that can reach up to 10 feet (3m) long. 

Producing a mass of lush heart-shaped leaves and trumpet-shaped flowers – they are part of the Ipomea family – this crop puts on an attractive display. Grow sweet potatoes either in borders, containers or grow bags outside or undercover, depending on the climate. When you plant sweet potatoes depends on your zone's climate, but a growing temperature of 70-80℉ (21-26℃) is ideal.  

Versatile in the kitchen and packed with vitamin C, antioxidants and minerals, the tasty tubers need little care and attention other than regular water and a fortnightly liquid high potash feed. Developing underground, this is a crop that should be hugely satisfying to dig up, but it’s worth recognizing exactly when they are ready to avoid disappointment.

‘Rich in vitamins and iron, sweet potatoes are delicious roasted, boiled, mashed or made into chips. The flowers and foliage are beautiful too, and the leaves can be cooked and eaten like spinach,’ says Rob Smith, Product Development Manager at Suttons.

When to harvest sweet potatoes

When foliage turns yellow

One indicator that sweet potatoes are ready to harvest is when the foliage turns yellow and begins to die back. Occurring in late summer and fall, before the arrival of the first frosts, this is the time to start investigating how well your crop has performed.

Four to five months after planting

‘Sweet potatoes are ready for harvest about four to five months after initial planting,’ says Madeline Pesso, Marketing Horticulturalist at seed retailer Botanical Interests. 

Once they reach a good size

‘Poke around the dirt where your originally planted your sweet potato to discover the size. Once you see a well-established potato, you may use a flat-tine digging fork or shovel, and dig widely around the hill to avoid damaging the sweet potato. Once the soil is loosened, you can pull the potato out by hand or by working up from underneath the potato.’ 

When the weather is fine

It’s also important to harvest the sweet potato tubers during fine weather, as any dampness or moisture can lead disease and rot setting in. 

Before the first frost

Handle carefully to prevent damaging the skins sure and space the crop apart somewhere dry with high humidity, for around two weeks, so the skins can harden or ‘cure’. 

Can you leave sweet potatoes in the ground too long?

Once they're ready to harvest, sweet potatoes can remain in the ground a few weeks longer and will continue growing larger but be sure to lift them before the frosts arrive otherwise the tubers are likely to be damaged.

How do you know when container grown sweet potatoes are ready to dig up?

‘Your sweet potatoes will be ready to harvest around four months after you planted them out in containers,’ says Rob Smith, Product Development Manager, Suttons. ‘The first sign is that the plants’ foliage will start to turn yellow and die back at the end of the season, which is a good sign that your tubers may be mature. 

'To harvest, gently lift them with a fork or turn out your container onto the ground. Remove any excess soil from the skin with a soft brush and set aside any bruised or damaged tubers to eat first, as they won’t store.’

Can you harvest sweet potatoes too early?

Yes, you can harvest sweet potatoes too early. It’s easy to be impatient when curious about a potential underground crop. Digging up sweet potato tubers too early – usually before September – often results in spindly tubers that are not as sweet or flavorsome as their larger counterparts. Leave them in the ground, water and feed regularly with liquid tomato feed to boost their size. Harvest before the first frost. 

How long do sweet potatoes take to grow?

Sweet potatoes take around three months to mature from slip to producing large, tasty tubers. Preferring warm temperatures of around 70-80℉ (21-26℃), they can be grown out in the open or under cover in a polytunnel or greenhouse. Harvest when the vines turn yellow and die back.