Growing Potatoes in Scotland: The Complete Guide

Solanum tuberosum

Everything you need to grow potatoes in Scotland, from chitting on a windowsill in February to lifting a maincrop in October. We have done the research so you don't have to.

Potatoes are the easiest crop on this site to grow and the easiest to lose. They ask very little of you, they do not mind our cool summers, and they crop well in ground that would defeat a tomato. The catch is blight, which arrives in a warm wet August and can strip a maincrop in days. Almost every decision on this page is really a decision about blight.

Choose your type first

Seed potatoes are sold as first earlies, second earlies or maincrop, and the choice sets your planting date, your spacing, your harvest and your blight risk in one go. It is the most consequential thing you will decide.

If you only have room for one type, grow first earlies. They are out of the ground by midsummer, which is the most reliable way to avoid blight without spraying anything or depending on a resistant variety. Maincrop is the ambitious choice in Scotland, not the default one.

Varieties

A long list of potato varieties carry the RHS Award of Garden Merit, and that matters more to check here than for most crops: it is a UK-wide award, not a Scottish recommendation.

Maris Piper is Britain's best-known potato and it is not among those named as blight-resistant, which makes it a risky default here however well it does further south. In a wet climate blight resistance is worth more than flavour or yield, because a maincrop that dies in August yields nothing at all. For earlies it matters far less. They are lifted before blight weather arrives, so grow whichever you like the taste of.

Soil and site

Potatoes want an open, sunny spot and rich soil with plenty of organic matter dug in. Compost or well-rotted manure worked in over autumn and winter is ideal. They are hungry and they are not fussy, which is a large part of why they suit Scottish gardens.

Do not lime the bed. Scab is far more common on alkaline soil, and our naturally acidic soils are one of the few conditions here that actively favours a crop. If you have been liming for brassicas, keep the potatoes somewhere else in the rotation.

Chitting

Chitting means sprouting the seed potatoes indoors before they go in the ground, and it buys you a couple of weeks. In a country where the season is the limiting factor, a fortnight is worth having.

Buy certified seed potatoes in February and stand them upright in egg boxes or trays, eyes pointing up, somewhere light, cool and frost-free. Four to six weeks later you want short, sturdy, dark green sprouts about a centimetre or two long. Long, pale, spindly sprouts mean the spot was too warm and too dark, and they snap off during planting.

Buy certified seed rather than planting supermarket potatoes, and if you are shopping in Scotland you are unusually well served. Seed potatoes produced and marketed here must be classified under the Seed Potato Classification Scheme, run by SASA, the Scottish government's agricultural science body, and Scotland is a major producer of quality seed potatoes. The certificate is a guarantee about disease status, which for a crop defined by disease is worth more than it sounds.

This is the second thing on this page Scotland is genuinely good at, after the blight forecasting. Quite why Scottish seed is so well regarded we will leave alone: there is a popular explanation involving our climate and the aphids that spread potato viruses, and we have not found it stated anywhere we would trust.

It is worth doing for earlies. For maincrop it is optional, because a maincrop has months in the ground to make up the difference.

Planting

Dig a trench about 15cm (6in) deep, set the tubers in with the sprouts facing up, and cover them. Spacing depends on type, as in the table above: earlies want less room than a maincrop, which needs both the space and the soil to bulk up.

Timing is keyed to your local last frost rather than a calendar month, because potato foliage is frost-tender and shoots take three to four weeks to appear. The aim is for them to break the surface as the frost risk is ending.

Earthing up

This is the job people underestimate, and it does two entirely separate things.

• It protects the shoots from frost. In much of Scotland the shoots appear while late frosts are still possible, and pulling soil over them is the standard defence. If frost is forecast and the shoots are up, cover them.
• It stops tubers seeing daylight. Exposed tubers turn green, and green potatoes are toxic and have to be thrown away.

Start when the shoots are about 20 to 23cm high, drawing soil up around the stems and leaving roughly the top 10cm showing. Repeat every few weeks as the plants grow, building a ridge of around 20 to 30cm. In containers, do the same thing by topping up with compost.

Watering and feeding

Potatoes in the ground rarely need feeding if the soil was prepared properly. On poor ground, a nitrogen-rich organic feed at the second earthing up will help a maincrop. Watering matters most during dry spells, and particularly as the tubers are forming.

Containers are the exception and they catch people out. The foliage spreads like an umbrella and keeps rain off the compost underneath, so a bag of potatoes can be bone dry after a wet week. Check by hand rather than by looking at the sky.

Blight: the one that decides your year

Late blight is the same organism on potatoes and tomatoes, and it is the reason Scottish maincrops fail. It needs warmth and prolonged wetness, and it spreads as wind-blown spores from other gardens and farms, which means a clean plot is not a safe plot. You cannot prevent it arriving. You can decide how much it costs you.

Four things genuinely help:

• Grow earlies. A first early lifted in June or July was never exposed to August blight weather. This is the most reliable defence available to a home grower.
• Choose a resistant maincrop if you want potatoes to store. See varieties below.
• Cut the foliage off once roughly a quarter of the leaves are infected. This is the decisive intervention: it stops spores washing down to the tubers. Leave the crop in the ground a fortnight afterwards before lifting.
• Clear every tuber at harvest, and pull up any volunteers that sprout next spring. Missed potatoes overwinter and sprout early, and they are a major source of the following year's outbreak.

That last one is worth taking seriously. Advisory services on both sides of the Irish Sea single out discarded potatoes and self-sown volunteers as a key early source of blight, and it is the job most growers skip.

There is no fungicide available to gardeners for blight. If someone tries to sell you one, it is not for this. Nor is any variety completely immune, so resistance lowers the risk rather than removing it.

The Hutton Criteria, and why it is ours

The warning system the whole UK uses to forecast blight risk was developed in Scotland, at the James Hutton Institute, and carries its name. It replaced a 1950s model that had gone unchanged for about sixty years and was missing outbreaks, and it works by watching for the specific combination of warmth and sustained humidity that blight needs.

Hutton also run Fight Against Blight, which has tracked outbreaks across the country through a network of scouts since 2006, and the BlightSpy service that forecasts when Hutton Criteria conditions are coming. Their potato breeding programme works on blight resistance using the Commonwealth Potato Collection, held in Scotland.

Nearly every Scottish angle on this site is a limitation: colder, later, wetter, shorter. This one is the opposite. The model every grower in Britain relies on to see blight coming came out of a Scottish research institute, and the national outbreak-tracking service is run from there too.

We are not printing the exact temperature and humidity thresholds, and we went looking before deciding that. They are repeated all over the internet, but Hutton's own pages name the criteria without defining them, so the numbers rest on secondary sources we will not publish as fact. Watch the blight forecast for your area instead. It does not require you to know the figures.

Harvesting

First earlies are ready when the flowers open or the buds drop, at around twelve weeks, with tubers about the size of a hen's egg. Have a careful dig under one plant to check. Second earlies follow a few weeks later. Lift both straight from the row as you want them, because they do not store.

Maincrop for storing is different. Wait until the foliage yellows and dies back, then cut it off and leave the tubers in the ground for about ten days so the skins harden. Lift on a dry day, let them dry off for a few hours, and brush the soil away rather than washing them.

Put a fork in about 30cm from the stem so you spear fewer of them. Store in paper or hessian sacks somewhere cool, dark, dry and frost-free, and look through them every few weeks for rot. Expect roughly 1 to 2kg per plant. Use them up before early spring, when they start sprouting on their own.

Common problems

• Potato blight is the dominant risk in Scotland and has its own section above.
• Slugs tunnel into maincrop tubers left in wet ground through autumn. Lifting promptly is the best answer, and Sarpo Mira resists them.
• Scab shows as rough patches on the skin. It is cosmetic and the potatoes are fine to eat. Avoid liming, and keep the soil moist as the tubers form.
• Green tubers are a light problem, not a disease. Earth up higher and earlier. Do not eat them.

Common questions

Sources