In summer, sweet potato leaves are at their tender best. They weren’t something people used to eat much. When did they become common? Probably when city dwellers began talking about “green food.” One year, they suddenly started appearing in the market, bundled into neat little bunches of young tips, said to lower blood pressure and to do all sorts of other things too.
Sweet potato vines grow fast in the heat. In a garden, if you plant a few roots and don’t expect much from the tubers, you can simply eat the leaves. The vines spread everywhere, the leaves are a bright green heart shape, with purple-red veins. You pinch off the tips, the youngest stretch of stem with a few leaves attached. After one picking, they grow back in a few days. The more you pick, the more they come. You can keep eating them all the way into autumn, day after day, and they never seem to run out.
The cooking is simple. Wash them clean, bring a pot of water to a boil, add a few drops of oil, and blanch the leaves until they soften. Then lift them out and rinse in cold water. That keeps them green instead of yellow. Smash some garlic into a bowl, add vinegar, light soy sauce, sesame oil, and a little salt. If you like heat, a spoonful of chili oil goes in too. Squeeze the blanched leaves dry, toss them into the bowl, and mix well. They taste slippery in a good way, with a little bite left, and the sweetness of the vegetable itself.
They can also be stir-fried. Heat the wok with cool oil, fry the garlic until fragrant, then add the sweet potato leaves and turn up the heat. A quick toss or two, and they’re done. They must not be cooked too long; otherwise they release too much water and turn limp and unappealing. Properly stir-fried, the stems stay crisp, the leaves stay tender, and there is a faint silky slickness to them. Some people like that texture, some don’t. Those who do say it’s a bit like water spinach, smooth and mellow. I’m in that camp.
One summer, I stayed for a few days in the countryside in Guangxi. There, people cook sweet potato leaves with something called sour bamboo shoots. The bamboo shoots are sliced into threads and stir-fried with the leaves, giving the dish a sour, spicy edge that makes it especially appetizing. I never quite got used to the taste of sour bamboo shoots, but the locals said that was exactly what gave it character. People in Hunan eat sweet potato leaves too, with fermented black beans and chilies, which makes for a different flavor altogether. One vegetable, many ways to cook it, and each version has its own logic.
When I was little, my grandmother only ate the stems. She stripped off the leaves, peeled away the outer skin, cut the stalks into sections, and stir-fried them with chili. Those stems were crisp and fresh, even better than the leaves. She used to say the leaves were hairy and rough on the throat. Later, as the varieties improved and the leaves became less fuzzy and more tender, she started eating them too.
These days, the sweet potato leaves sold in the market are mostly tender tips, much better than they used to be. Buy a bunch, blanch it, toss it with mashed garlic, and you can finish a whole plate. After eating them, your stomach feels clean and light, as if it has been rinsed through. I don’t know whether they really lower blood pressure, but they do feel good to eat, and that much is true.