One of our all-time favourite meals at home is a sweet potato “gratin”, the roots sliced quite finely and then mixed with ginger, lime, coconut milk, chilli and garlic, and baked in a roasting tin for an hour (see below).
It goes with everything and is equally great on its own or maybe with a salad. However, when it comes to growing sweet potatoes, ever since I visited Bob Flowerdew 20 years ago to see the unusual veg he grew (and to write about it for this paper), I have felt it was better to buy them.
Flowerdew had his sweet potato crop in a double polytunnel, one mini tunnel within another. He felt that to get a root size worth bothering with, these lovely orange-fleshed tubers needed a longer growing season than we had in the UK. He told me our autumns were just too cold.
As a result of climate change and our now typically longer autumns, as well as the availability of varieties bred for our shorter-than-American growing season, Tom Brown, head gardener at West Dean in West Sussex, decided to trial sweet potatoes last summer to see if things had changed.
Not only do I love eating sweet potatoes (or Ipomea batatas, to give them their botanical name), I love how they look. I have done ever since I saw them grown as houseplants in a flat in Paris. Grown much like an avocado, the friends I visited had so-called ipomoea “slips” with their roots in water, the tuber suspended above.
Sprouting out the top like Jack’s beanstalk were 20ft-long runners with brilliant green, heart-shaped leaves trained all around one of those huge and glamorous Parisian studio windows.
I’ve remembered it ever since, so when Brown invited me to go to the West Dean sweet potato weigh-in, I was in. There’s no doubt that on square-inch productivity, and time needed to water and feed, sweet potatoes are not winners, but I’m now convinced to grow them as an ornamental edible, if not for the harvest alone.
Brown also makes the point that sweet potatoes are such vigorous growers, they make great weed suppressants. The West Dean greenhouse had an invasion of oxalis all through its bed, but the combination of hugely strong root growth from the sweet potatoes and the weed-suppressing membrane wiped out the oxalis completely.
This year, Brown is planting the heaviest croppers in a wide south-facing border outside to see how they do, and I’ve been inspired to grow all three varieties for our greenhouse in great willow baskets here, too.