The sweet potato is winning over German gardens, and quite rightly: it is robust, vigorous and yields tubers that thrive surprisingly well in your own bed. There is just one thing to understand, or you end up puzzled by pale, mealy tubers: it is not related to our potato and wants very different treatment.
Instead of a nightshade, you have a warmth-loving bindweed here. That explains why it is propagated from cuttings and why, after harvest, it needs one more secret to turn sweet. One step at a time.
Not a potato, a bindweed
The sweet potato belongs to the bindweed family, just like the morning glory in the ornamental garden. Its heart-shaped leaves and long, creeping runners give the relationship away at once. Botanically it has nothing to do with the potato (Solanum tuberosum).
That has two practical consequences. First, its leaves are edible and taste like a mild leafy vegetable, whereas potato foliage is toxic. Second, it does not propagate from seed tubers but from rooted shoots. And those you raise yourself.
How to grow sweet potatoes
Sprout the slips
From February, lay a tuber warm and bright in moist soil or half in water. After a few weeks it drives runners, the so-called slips. Alternatively, buy ready seedlings.
Root the shoots
Cut the shoots off at about 15 cm and stand them in a glass of water. In one to two weeks they form roots and are ready to plant.
Plant out warm and late
Set the cuttings into the bed only after the last frosts, around CW 19 to 22. A small ridge with black mulch film stores warmth and gives the best yields.
Let it ramble, water moderately
The runners spread widely and shade the ground. Water in dry spells, but do not keep the plant permanently wet, or the tubers rot.
Harvest before frost
Dig up the tubers before the first frost, usually in October (CW 40 to 42). Work gently: the thin skin is delicate and bruises rot easily.
The secret of the sweetness: curing
Fresh from the ground, the sweet potato tastes rather bland and mealy. It only gains its famous sweetness through one last step that many people skip.
A bindweed, not a nightshade. Plant warm, cure warm, but never store it cold.
The core rule for sweet potatoes
Frequently asked questions
Is the sweet potato related to the potato?
No. It is a bindweed (Ipomoea batatas), related to morning glory and field bindweed. The potato, by contrast, is a nightshade. Only the name and the tuber shape are similar.
How do I raise my own cuttings?
Sprout a tuber warm and bright from February in moist soil or half in water. Cut off the shoots that form and root them in a glass of water. After one to two weeks they are ready to plant.
Why does my harvest not taste sweet at all?
Because the curing is missing. Freshly dug, the sweet potato is mealy. Let it sweat warm and humid for one to two weeks, and the starch turns into sugar and it turns sweet.
Can the sweet potato go in the fridge?
No. Below about 10 degrees it takes cold damage, turns hard and loses flavour. Store it dry and cool at 13 to 15 degrees, for example in a frost-free pantry.
Can I eat the leaves?
Yes, and it is a nice bonus. Unlike the toxic potato foliage, the young sweet potato leaves are edible and taste like a mild leafy vegetable, briefly steamed like spinach.
