In the UK, start chitting seed potatoes around 4 to 6 weeks before planting. This guide explains when to start. It also tells you how much light they need. You will learn what good chits look like. Finally, it shows how to fix long, weak sprouts.
- When to start: count back 4 to 6 weeks from planting. Many UK growers start first earlies late January to early February, second earlies in February, and maincrop from mid-February onwards.
- What good chits look like: They are short, around 1 to 2 cm. They should be firm sprouts with a green or purple tint. Avoid long white stems.
- Common mistake: chitting in a warm, dim place (or leaving tubers piled in a net bag). Fix it by moving to brighter, cooler conditions and reducing the number of sprouts you keep.
Growing your own potatoes may not be a big cost saving but it is enjoyable and satisfying. I always start my seed potatoes by chitting them at home to give them a head start.
Start at the right time
Successful chitting starts with timing it to when you can realistically plant. Seed potatoes usually need around 4 to 6 weeks in a cool, bright place before planting. If you start too early and cannot plant for ages, sprouts overgrow and weaken. In colder UK areas, delay chitting by a week or two. This prevents the shoots from outgrowing the tray while the soil is still cold.
| Potato type | Typical UK chitting start window | Target sprout look | Notes for cold areas |
|---|---|---|---|
| First earlies | Late January to early February | Short (around 1 to 2 cm), firm, coloured sprouts | Start a week later if you plant later. Keep frost-free. |
| Second earlies | Early to mid-February | Short, firm, coloured sprouts | Delay to late February if spring is slow where you are. |
| Maincrop | Mid-February to early March | Short, knobbly sprouts (not long and white) | Chitting is optional. If space is tight, you can skip it. |
If you want a deeper dive into choosing and storing tubers, see our guide on preparing seed potatoes for planting.
UK references: RHS: Grow your own potatoes and Thrive: Chitting potatoes.
Set up for strong chits
Remove your seed potatoes from net bags and look for the blunt “rose” end with the most eyes. Stand each tuber upright in an egg box or seed tray with the rose end facing up. Keep them in a light, frost-free place such as a porch, spare room, or unheated greenhouse. The key is cool plus bright so chits develop slowly and strongly.
Check weekly. If you get lots of sprouts on one tuber, remove the weakest extras. This allows the potato to focus on fewer, stronger shoots. Fewer shoots usually means fewer but larger potatoes. More shoots usually means more but smaller potatoes. Keep the tray dry and airy.
- Rose end up, one layer only
- Bright daylight (windowsill, porch, greenhouse)
- Cool and frost-free
- Rotate the tray every few days for even light
For seasonal context, see seed potatoes arrive.
Use enough light
Light is the secret to strong chits. Place the tray in bright daylight where it stays cool. Good chits are short and firm, often with a green or purple tint. Too little light, especially combined with warmth, produces long, pale, brittle sprouts. I always chit my potatoes on a shelf in my unheated greenhouse.
If you are unsure whether your spot is bright enough, use the sprouts as your measurement. Short and coloured means you are close to ideal. Long and white means move them to a brighter, cooler place.
| Light and temperature decision card | Action |
|---|---|
| Short, firm, slightly coloured sprouts | Ideal. Keep them cool, bright, and frost-free. Rotate the tray for even light. |
| Long, thin, white sprouts | Too dim, too warm, or both. Move immediately to brighter daylight and a cooler spot. |
| Bright spot but frost risk overnight | Cover with fleece or newspaper overnight, or move indoors for the coldest nights. |
| Sprouts keep stretching after you move them | Reduce warmth first (away from radiators and heated rooms), then increase light. |
If you want more on managing indoor light in the UK, see starting seeds early in the UK.
Avoid the weak-sprout mistake
Long, pale sprouts are not a sign your potatoes are “keen”. They are a sign the setup isn’t ideal. The most common cause is chitting in a warm, dim environment, which makes sprouts stretch. Leaving tubers piled in delivery nets or sacks does the same thing. The other common cause is starting too early, then being unable to plant when spring is slow.
- Do not chit in the dark: cupboards, sacks, and net bags produce weak, white sprouts.
- Keep it cool: central heating speeds growth and makes sprouts leggy.
- Avoid damp: keep the container dry and airy to prevent rot.
- Time it to planting: aim for 4 to 6 weeks, not months.
Fix weak sprouts safely
If your seed potatoes already have long, pale sprouts, you do not have to throw them away. The aim is to stop the stretching, strengthen what you keep, and plant without snapping everything off.
- Move to brighter, cooler conditions now: this is what stops leggy growth.
- Handle gently: move the whole tray rather than lifting potatoes by the sprouts.
- Rub off weak extras: keep only the strongest few sprouts so the tuber supports sturdier stems.
- If sprouts are very long and brittle: remove the worst ones and let fresh, sturdier chits form in better conditions.
- Plant sooner rather than later: once conditions allow, plant carefully so sprouts are not knocked off.
If tubers feel soft, smell unpleasant, or show obvious rot, discard them. Healthy seed potatoes should feel firm.
Know what to do next
When the weather and soil are ready, plant chitted potatoes gently so the sprouts are not snapped off. Your seed potato supplier notes and RHS guidance are worth following for depth, spacing, and variety-specific timing. If you garden in a small space, containers and grow bags can be easier. They are also more reliable if your soil stays wet. See our piece on growing potatoes in bags.
For a seasonal overview of what else to sow around the same time, check out what to sow in March.
FAQs
When should I start chitting potatoes in the UK?
Do I need to chit maincrop potatoes?
How much light do chitting potatoes need?
Why are my sprouts long and white?
Can I plant seed potatoes with long sprouts?
How many chits should I leave on a seed potato?
Conclusion
Chitting seed potatoes is simple, but it works best when you get the timing and conditions right. Start 4 to 6 weeks before planting. Keep tubers cool and frost-free. Give them bright daylight so sprouts stay short and sturdy. If sprouts go long and white, address this as a setup problem. Adjust the light and temperature. Plant as soon as conditions allow.
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