‘Arran Pilot’ shows good resistance to potato scab
Image: Potato ‘Arran Pilot’ from Thompson & Morgan

Potatoes are easy to grow and take very little time and effort to look after once they’re in the ground. But there’s one disease that can scupper your plans and spoil your crop – potato blight. We asked guest blogger Richard Barrett for his expert advice on how to avoid this pesky problem. Here are his top tips for preventing potato blight.

What are the benefits of growing your own potatoes?

‘Charlotte’ potatoes can be grown without chemicals
Image: Potato ‘Charlotte’ from Thompson & Morgan

Potatoes started life as food for the poor but have quickly become a favourite vegetable for everybody. I like to grow my own potatoes because then I’m able to control the conditions in which they’re grown.

Commercially, the plants are often sprayed repeatedly with fungicide to safeguard against blight and then the foliage is knocked back by herbicide before harvest. This seems a poor environment for a healthy food crop.

How to prepare the ground for potatoes

Potato ‘Java’ has excellent disease resistance
Image: Potato ‘Java’ from Thompson & Morgan

So I have my own potato patch. It has light soil that doesn’t waterlog, lots of sunshine and is free of tree roots. Also, the land around slopes away, so it’s not a frost pocket where the cold air can flow into. The soil is alkaline, and this can mean the tubers may have scab on their skins, but this diminishes when potatoes are grown regularly in the same soil as a micro-organism builds up that prevents scab. That doesn’t mean that I don’t use crop rotation, but often the same patch is used every other year.

I make lots of cold compost, where garden waste is processed in a big heap and left to its own devices for a year. So I apply the compost to the ground early in the year for the rain to wash the goodness in, and any coarse particles are raked off to go back into the new heap. Although cold compost contains viable weed seeds, this doesn’t matter because the leafy potatoes smother any weed seedlings. I also apply seaweed meal to the soil so my plants have extra minerals for growing. These will hopefully enter the potato tubers too. Keeping the vegetable plot free of weeds and in good cultivation keeps pests like wireworm and slugs at bay.

The best way to plant seed potatoes to avoid blight

Plant tubers to a depth of 6 inches
Image: rodimov/Shutterstock

From St Patrick’s Day onwards I start planting the seed potatoes in order of variety – first earlies first, working through to maincrop, until the process is completed by Easter. I plant to a depth of six inches and leave all well alone until I see small sprouts of potato leaves appearing on the surface of the soil. Then, in stages, I start to earth up the sprouting leaves forming a trench either side of the row. If frost threatens, then I earth up completely covering the new shoots, otherwise they can be left just showing. Early planting is worthwhile as the potatoes stand a good chance of cropping before blight emerges in late summer.

What is potato blight?

Late potato blight rots the tubers from within
Image: Thy/Shutterstock

There are two types of blight: early blight which discolours the foliage inhibiting the plants’ growth; and late blight which is far worse and appears as black/brown necrotic spots in August and September. Late blight gradually defoliates the plants and then enters the tubers causing them to rot from within, making them inedible.

Best blight-resistant potatoes

Potato ‘Sarpo Mira’ is best in class for blight resistance
Image: Potato ‘Sarpo Mira’ from Thompson & Morgan

Much has been written in seed catalogues about which blight-resistant potatoes to choose. The best advice is to grow a range of varieties, that way you can reap the benefits of potato growing whatever the weather. Early blight is a nuisance but tolerable; picking off poor leaves can help the plant. When late blight appears you must immediately cut all the foliage away to soil level. Some varieties such as Sarpo Mira can resist blight, so the leaves of those can be left growing.

What is not often mentioned is the difference between thick and thin-skinned potatoes. The tubers of a thick-skinned variety like Cara can be left in the ground where they remain fresh and full of moisture, then lifted as required for the kitchen. Whereas Orla is a tasty variety with beautiful foliage that resists early blight, but is thin-skinned and must be harvested as soon as possible or the tubers will be damaged by pests such as slugs and wireworm.

Whatever varieties you choose, or method of cultivation, the potato is a very rewarding and nutritious vegetable to grow. For more potato stories and advice, take a look at our hub page.

Richard Barrett

I have held an allotment since 1987 and am now secretary for the association. I like to grow my vegetables as naturally as possible but have an open mind towards technology and it’s products. I usually enter the competition organised by the federation of local allotments and have achieved a certificate of merit for my plot, but have never won outright as work commitments inhibit my efforts to have the plot that tidy. I won a first prize for my cherry tomatoes in the Royal Oxfordshire Horticultural Society Show in 2009.