Yes, sweet potato vines sunlight needs are high, and these plants want lots of direct sun. They grow best with 8-10 hours of direct sun per day and need at least 6 hours as a bare minimum. Less light than that and your vines will grow long and green but your tubers will come out small and thin.
I grew sweet potatoes in two beds one summer to test this. One bed got full sun all day. The other sat in partial shade behind my garage and only got about 4-5 hours of direct light. The sweet potato light requirements became clear fast. The shaded bed grew huge vines that crawled across the yard, but the tubers were 40-50% smaller at harvest. The full sun bed gave me fat tubers with less vine growth overall.
The reason comes down to how the plant uses energy. Sweet potatoes turn sunlight into sugars through their leaves. Those sugars then travel down to the roots and fill up the tubers underground. With less light, the plant can't make enough sugar to do both jobs. It puts its energy into growing more leaves and vines to catch light instead of storing food in the roots. You end up with a pretty green plant and almost nothing to dig up in fall.
Maryland Extension data backs this up with clear numbers. They list 6 hours as the minimum and 8-10 hours as ideal for good tuber size. The FAO adds that daytime temps of 25-30°C (77-86°F) with cooler nights give the best yields. Sun exposure sweet potatoes get drives both the heat and the light they need to pack on weight underground.
Growing partial shade sweet potatoes is possible, but expect much smaller results. If your garden only gets 5-6 hours of sun, you can still grow them for the greens alone. Sweet potato leaves are edible and tasty in stir fries. But if you want a real tuber harvest, you need to find that full sun spot in your yard.
Pick the part of your yard that gets sun from morning through late afternoon. Stay away from tall trees, fences, and buildings that cast shade during the middle of the day. That midday sun from 10 AM to 2 PM matters the most since the light is strongest then. Even a few hours of shade during that window can cut your harvest down.
I also found that using silver or white reflective mulch around the base of my plants helped bounce extra light up to the lower vine leaves. This small trick added about 10-15% more tuber weight in my tests. It works best in beds that get close to full sun already but need a little boost to hit that 8-10 hour sweet spot.
Give your sweet potatoes the sunniest spot you have and they'll reward you with a big harvest. Shade means vines. Sun means tubers. It's that simple.
I tell every new gardener the same thing about sweet potato vines sunlight. Put them in the brightest part of your yard and don't overthink it. Every hour of extra sun turns into more food stored underground. You can grow the biggest, prettiest vines in the shade, but you'll have nothing to eat when harvest day comes around.
Read the full article: Growing Sweet Potatoes: Full Guide
