Potatoes

If a household grows one thing for food rather than for pleasure, it should be potatoes. They give more food energy per square metre than anything else that grows reliably in Britain, they need no processing, they store for months with no equipment, and they are among the easiest crops there are.

They also break up rough ground, smother weeds, and give a household with children something genuinely enjoyable to harvest.

Why potatoes first

Around 3 to 5 kilograms per square metre in a decent domestic bed, at roughly 770 kcal per kilogram. That is somewhere near 2,300 to 3,800 kcal per square metre, which is several times what most garden crops manage. See grow for calories, not for salad for the full arithmetic.

They store without processing. No canning, no drying, no freezer. A cool dark frost-free place and they keep for months.

They are forgiving. Poor soil, a first-year bed, a wet summer, a distracted gardener. They still produce something.

They prepare ground. The foliage suppresses weeds and the earthing up and lifting break up compacted soil, which is why they are traditionally the first crop on newly broken ground.

Seed potatoes and chitting

Buy certified seed potatoes. They are produced under inspection to limit virus and disease carry-over, and they are inexpensive.

Do not plant supermarket potatoes. They may carry disease into your soil for years, many are treated with a sprout inhibitor, and the variety is often unsuited to the conditions. It occasionally works and it is a poor risk for the sake of a few pounds.

Chitting means sprouting them before planting, and it brings the crop forward by a couple of weeks.

1. From late winter, stand the seed potatoes in egg boxes or trays, rose end up. The rose end is the one with the most eyes.
2. Somewhere cool and light, around 10 degrees. A spare room windowsill or a frost-free porch.
3. Wait until the sprouts are about 2 centimetres, short, stubby and dark. Long pale sprouts mean too warm and too dark.
4. Rub off all but three or four sprouts for larger potatoes, or leave them all for more, smaller ones.

Chitting matters most for earlies and makes little difference to maincrop.

Which type to grow

For storage you need maincrop, and maincrop is what gets blight.

For reliability, earlies win, because they are lifted before blight typically arrives. In a wet summer the earlies come in and the maincrop does not.

The sensible plan is both. Earlies for eating through summer and for a guaranteed crop; maincrop for the store, accepting the risk.

Look for blight-resistant maincrop varieties. The Sárpo types in particular are bred for it and are genuinely much more resistant, at some cost in texture and flavour. In a wet British summer that trade is usually worth making.

Planting

• When the soil is workable and the worst frost has passed. Earlies from March, maincrop through April. Soil temperature matters more than the date.
• Trench or dibber. A trench about 12 to 15 centimetres deep, or individual holes.
• Spacing: earlies about 30 centimetres apart in rows 50 centimetres apart; maincrop about 40 centimetres apart in rows 75 centimetres apart. Crowding reduces the total crop.
• Sprouts upwards.
• Cover with soil or compost.
• On a no-dig bed, lay the seed potatoes on the surface or in a shallow depression and cover with 15 centimetres of compost. They grow perfectly well and lifting is far easier. See starting a bed.

Frost kills emerging foliage. If shoots are up and frost is forecast, draw soil over them or cover with fleece. The plant recovers from a frosting and it costs you time and yield.

Earthing up

Draw soil or compost up around the stems as the plants grow, two or three times, until you have a ridge.

It does two things, and the second is the important one:

1. Increases yield, because tubers form on the buried stem.
2. Keeps light off the developing tubers, which is what stops them going green.

Start when the shoots are about 20 centimetres and repeat as they grow. Mulching heavily with straw or compost achieves the same thing with less work.

Blight

The thing that will beat you, in a wet summer, and it is worth recognising early.

What to do the moment you see it:

1. Cut off and remove ALL the foliage immediately, right down to the ground. This is the whole intervention and it works.
2. Take it away. Do not compost blighted material and do not leave it lying on the bed.
3. Leave the tubers in the ground for at least two weeks before lifting, so that any spores on the soil surface have died off rather than being carried down to the tubers as you dig.
4. Then lift, and store only sound tubers. One infected potato will rot a sack.

Prevention, such as it is: resistant varieties, wide spacing for airflow, not watering the foliage, earlies lifted before it arrives, and never leaving old potatoes or volunteers in the ground over winter, which is where it overwinters.

Tomatoes get the same disease. Keep them well away from potatoes, and do not grow outdoor tomatoes next to a maincrop bed.

Lifting and curing

• Earlies: lift as you need them, once the flowers open. There is no storage stage.
• Maincrop: cut the foliage down two weeks before lifting, whether or not there is blight. It sets the skins.
• Lift on a dry day, carefully, with a fork well away from the row. Every fork wound is a route for rot.
• Leave them on the surface for a few hours to dry, if the weather allows.
• Then cure: a few days somewhere dry, dark and airy at around 10 to 15 degrees, which toughens the skins for storage.
• Sort ruthlessly. Any potato that is damaged, cut, soft, or shows any dark patch goes in the eat-now pile, not in the store.

Storing them

Hessian or paper sacks, or slatted trays. Never sealed plastic, which sweats and rots them.

Check them monthly and remove any that have gone soft. One rotting potato spreads.

A shed, garage, cellar or outbuilding works if it is frost free. A kitchen is too warm and they sprout. A fridge is too cold and turns the starch to sugar. See root cellaring.

Keep some as next year's seed only if you have to. Home-saved potatoes accumulate virus over generations and yields fall, so buying certified seed each year is worth it while you can. Saving your own for a season or two is a reasonable fallback and not a long-term plan.

Green potatoes and what not to eat

Growing in containers

Genuinely productive, and the answer if you have no ground.

• Any container over about 40 litres. A bucket with drainage holes, a builders' trug, a purpose-made sack, or a compost bag stood upright with the top rolled down and holes punched in the bottom.
• Two or three seed potatoes per large container.
• Start with 15 centimetres of compost, put the potatoes in, cover, and top up with more compost as the shoots grow until the container is full. That is earthing up.
• Water often. Containers dry out fast and potatoes are thirsty, and drought at the wrong moment cuts the crop badly.
• Feed with a liquid feed once the plants are established. See soil and compost for comfrey feed.
• Tip the whole thing out onto a sheet to harvest, which is the best part.

First earlies do best in containers, and a container crop started in late summer indoors or in a greenhouse can give new potatoes at Christmas.