Chitting Seed Potatoes: Why and How

If you have just bought a net of seed potatoes and seen "chit before planting" on the label, this guide is for you. Chitting is one of those small jobs that sounds far more technical than it is — and for early potatoes, it can earn you an extra week or two of harvest for almost no effort. Here is what it means, why it helps, and exactly how to do it.

What chitting is

Chitting simply means letting your seed potatoes start to sprout before you plant them. You stand the tubers somewhere cool and light for a few weeks, and they grow short green shoots from the little dimples on the surface — the "eyes". When you plant a chitted potato, those shoots are already up and running, so the plant gets going faster once it is in the ground.

That is the whole idea. You are not doing anything to the potato except giving it the right conditions to wake up gently before planting day. A chitted tuber and an unchitted one will both grow into a perfectly good plant — chitting just gives the chitted one a head start.

It helps to picture what the eyes are. Each one is a dormant growth bud, much like the buds on a tree in winter. Left in the dark in a warm kitchen, they produce long, pale, weak shoots that snap off easily. Given cool air and good light instead, they produce short, sturdy, dark-green shoots that travel with the tuber intact when you plant it. Getting those good shoots is the entire aim of the exercise.

Why chit at all

The honest answer is that chitting matters most for early potatoes and much less for maincrop.

First and second earlies — the varieties you plant in spring for new potatoes in early summer — are racing the clock. The sooner they crop, the better, partly because new potatoes are a treat worth having early, and partly because getting them lifted by midsummer helps you dodge the worst of potato blight. Chitting brings the harvest forward by roughly a week or two, which on a fast crop like this is a real gain.

Maincrop potatoes are a different story. They are in the ground for a long season anyway, building large tubers for storing through autumn and winter, so a few days' head start makes little difference to the final crop. You can chit maincrops if it is convenient, but you can just as happily plant them straight from the bag. Do not feel you have failed if you skip it.

There is a second, quieter benefit. Standing your seed potatoes out in the light for a few weeks lets you spot any that are soft, mouldy or refusing to sprout. You can throw those out before they take up space in the ground, so every tuber you plant is one you trust.

When to start chitting in the UK

In most of the UK, you want to start chitting in late January or February. The rule of thumb is to begin about six weeks before you plan to plant.

That timing works backwards from the weather. First earlies generally go in from mid-March in milder parts of the country, a little later in the cold north or on exposed sites — the young foliage is frost-tender, so you are waiting for the worst frosts to pass. Counting back six weeks lands you in early-to-mid February for the start of chitting, which is why seed potatoes appear in garden centres and seed catalogues from the new year onwards.

If spring is running cold and the ground is still sodden, do not panic about planting dead on schedule — potatoes are forgiving. It is better to hold the chitted tubers a little longer in their cool, light spot than to plant into cold, wet soil that will only rot them. To pin down your own local planting window, check your last frost date with the frost date checker and line the whole crop up on the planting calendar.

How to chit, step by step

You need almost nothing for this — your kitchen recycling has most of the kit already.

1. Find some egg boxes or a shallow tray. Cardboard egg boxes are the classic choice because each cup holds one tuber upright and stops it rolling. A seed tray, an open mushroom box or any shallow container lined so the potatoes sit in a single layer works just as well.

2. Stand each potato up the right way. Look at the tuber and you will see that one end has more eyes clustered together — this is the "rose end". Set each potato with the rose end (the eyes) pointing up. This is where the strongest shoots come from, so you want them growing into the open air rather than buried in the cup.

3. Put them somewhere cool, light and frost-free. Aim for around 10°C — a porch, a spare bedroom windowsill, a frost-free shed, garage or a cool conservatory are all ideal. The two things that matter are good light and gentle cool. Light keeps the shoots short and stocky; cool keeps them from racing away.

4. Avoid the two common mistakes. A warm, dark cupboard is exactly wrong — it gives you long, pale, brittle shoots that snap off the moment you handle the tuber. A hard frost is the other danger, as it will damage the seed potatoes outright. Light but cool is the sweet spot.

5. Wait four to six weeks. Check on them now and then, turning any that are leaning towards the light. There is nothing else to do but let them get on with it.

You are aiming for shoots about 1.5 to 2.5cm long — short, stubby and dark green or purplish, roughly the length of your thumbnail to the first knuckle. Those are the shoots that will survive planting and power away in the soil. Long, white, thread-like shoots mean the tubers have been too warm and too dark; if that happens, move them somewhere brighter and cooler and handle them very gently from then on, as they break easily.

How many shoots to keep

Once your seed potatoes have chitted, you can decide how many shoots to leave on each one — and this is a genuine lever on what you harvest.

• For fewer but bigger potatoes, rub off all but the strongest three or four shoots with your thumb, choosing the sturdiest ones near the rose end. With less competition, each shoot tends to produce larger tubers. This is the usual advice for first earlies, where good-sized new potatoes are the goal.
• For more but smaller potatoes, leave all the shoots in place. You will get a heavier number of tubers per plant, though individually they will run a little smaller. This suits maincrops destined for the store, or anyone who simply wants the biggest possible count.

There is no wrong answer — it comes down to whether you would rather have a handful of generous potatoes or a basketful of small ones. If you are not sure, leaving four good shoots is a sensible middle road. Use your thumb to gently rub the unwanted ones off; there is no need for a knife.

From chitting to planting

When planting day arrives and the soil has warmed, your chitted tubers go straight into the ground or a container, shoots pointing up, around 12–15cm deep. Carry them out cupped in your hands or in their egg box so the shoots stay intact — that is the only delicate moment in the whole process.

From there, the next jobs follow on quickly. As the leafy shoots push up through the soil, you will start earthing up your potatoes — drawing soil up around the stems to protect the new tubers from light and frost and to encourage a bigger crop. And if you have no veg bed at all, the same chitted potatoes do brilliantly in pots, sacks and tubs, which is covered in our guide to growing potatoes in containers.

For the full picture from buying seed to lifting your first new potatoes, head back to the main potato growing guide, which ties the whole season together. Chitting is just the gentle first step — and as first steps go, it is about as easy as gardening gets.