This is my first year growing potatoes and I’ve noticed some of them have pushed up slightly out of the ground close to the base of the plant and have turned green. A gardening friend said these are poisonous and not to eat them. Is this true? And how do I stop it happening again?
Your friend is correct. When the flesh of a potato is exposed to bright sunshine for a prolonged period, it causes it to produce two chemicals, or glycoalkaloids, as a way of warding off attack from insects. Consumption of these bitter-tasting toxins, which are known as solanine and chaconine, can cause severe stomach upset, headache, fever, disturbed vision and disorientation.
Unfortunately cooking the affected potatoes doesn’t prevent this from happening as these chemicals only begin to break down at temperatures of between 230 and 280 degrees. This is why potatoes are traditionally sold in brown-paper sacks to prevent their exposure to bright sunlight. It’s also why any freshly harvested potatoes should be kept n a cool, dark place to prevent them from greening up.
If the greening is only to a very slight degree and on a small part of the potato, it’s generally considered safe to cut the affected section away and discard the latter. But with badly affected potatoes, don’t eat them at all and instead dispose of them on the compost heap.
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To prevent it from happening again, it’s important to regularly earth-up around young potato plants as the tubers begin to develop underground from late spring. Along with protecting the tubers from exposure to bright sunlight, this also helps protect them from frost and encourages a bigger harvest.
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You’ll need to start earthing-up when the plants are no more than about 25cm tall, using a hoe or trowel to raise a ridge of soil around the plant so that only about half the stem (12cm or so) remains visible above ground. Repeat this process several times, leaving a couple of weeks to elapse each time before you do so, while also making sure to avoid damaging the plants’ root systems.
Over time, this will result in a raised ridge of soil or compost about 25cm-35cm around the plants, enough to keep any developing tubers safe from exposure to sunlight. If you’re growing in containers, make sure to leave enough room to allow for this process at the planting stage.
