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Keep your tatties in the dark by earthing them up. Gardeners have long known that when exposed to light, the skins turn green which is a sure sign that they contain the poison, solanine.
Solanine is produced as a natural defence against insects, disease and herbivores and in large quantities it poisons us as well.
The symptoms are often similar to food poisoning and in extremely rare cases can cause death. In Scotland in 1918, there were 61 reported cases of this poisoning, including the death of a five-year-old child.
The poison accumulates on the skin of green potatoes and studies have shown that boiling or frying doesn’t get rid of it.
So don’t buy green potatoes that have been sitting too long on supermarket shelves, and stop light getting to ones you’re growing. You can’t follow the usual rules with tubers and sink to a depth 3 times their size. It’s not deep enough for 2 reasons: how potatoes grow and how they react to light.
Firstly, potatoes grow on a plant’s stem above, not below, the seed potato. So, some tubers will inevitably be close to, or break, the surface. Some varieties, like the Mayan group, are what I call ‘ground huggers’: they seem determined to break surface, however deeply you sink the mother tubers.
Secondly, potatoes don’t need to lie on or just below the surface to start greening. Light at the red end of the spectrum penetrates the soil to several centimetres. Unfortunately it’s known that red light stimulates the production of poisonous solanine.
We try to prevent this by planting tubers quite deeply. There are several different methods. They include: digging a trench, planting the tubers 20-25cm deep and earthing up; making holes 15-20cm deep and covering with mulch as the plants grow; or placing the potatoes on the surface and piling on a deep layer of organic mulch.
As for the third option, I couldn’t produce enough mulching material at home or afford to buy it in. I have tried the second one with 1st Earlies and wasn’t much impressed by the results, but do like first approach.
As a convert to no-dig, I keep soil disturbance to an absolute minim. And I wouldn’t dream of using a rotovator, however fine and easy to rake the soil becomes.
So, what’s the best way forward after planting? In a recent study Which? Gardening assessed the best ways of excluding light and producing the heaviest crop of clean, healthy tubers.
Researchers trialled 4 different techniques: traditional earthing up, and 3 types of mulch – farmyard manure, grass and strulch [a straw-based material].
Undoubtedly planting seed potatoes and covering with mulch was the easiest method. Strulch produced the largest crop of clean pest-free tatties, but strulch ain’t cheap and cost a staggering £3 per kilo. Grass clippings, free of synthetic fertiliser and herbicide concoctions of course, were the free alternative, but didn’t exclude enough light or keep slugs at bay. I’ve found grass also produces a flush of weeds. Researchers didn’t assess the benefit of placing a thick layer of newspaper beneath the grass. This does exclude light and prevents weed germination.
Farmyard manure could be expensive. It did give a large crop, but unfortunately many green potatoes.
Researchers found that good old-fashioned earthing up was free and provided the second largest crop with very little greening. As potato leaves emerge above the surface, soil is drawn over them, by raking from each side of the row to form a wide inverted V.
Repeat the process 2 or 3 weeks later. It’s a sair fecht with a bad back, but looks great and earns a brimming mug of tea.
Plan of the week
Geum ‘Flames of Passion’ bears strong, red, semi-double flowers on upright stems above a mound of scalloped foliage. It flowers for many weeks and prefers a moisture retentive soil.
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