Chitting is the cheapest trick in potato growing. It costs nothing, takes ten minutes to set up, and buys you roughly two weeks at the other end of the season. All it needs is an egg carton and a bright window in a cool room.
It also goes wrong more often than almost any other seed-starting job. The seed potatoes get tucked into a closet "to sprout", and by planting day every tuber carries six-inch white shoots that snap the moment you lift them. That is the opposite of chitting, and the difference comes down almost entirely to light. This guide covers how to control it, plus the two-stage temperature routine most advice leaves out.
Chitting potatoes at a glance
| Detail | Value |
|---|---|
| What it is | Sprouting seed potatoes in light and cool air before they go in the ground |
| Other names | Greensprouting, pre-sprouting, presprouting, green sprouting |
| When to start | 3–6 weeks before planting; four weeks is the standard |
| Stage 1, breaking dormancy | 18–21 °C (65–70 °F) for 5–10 days |
| Stage 2, greening | 10–13 °C (50–55 °F), as bright as you can manage |
| Light | Bright indirect daylight, never scorching direct sun |
| Sprout length at planting | 1–2.5 cm (1/2–1 in), thick and stubby |
| Sprout colour | Green, blue-green or purple depending on variety |
| Sprouts to keep | 3–4 per tuber as a default |
| Equipment | Egg carton, seed tray, fruit flat or shallow box |
| How to set the tuber | Single layer, rose end (most eyes) facing up |
| Time gained | 10–14 days earlier harvest |
| Benefits most | First earlies and second earlies |
| Benefits least | Maincrop varieties grown for winter storage |
| Frost tolerance | None — sprouts are killed by frost, keep frost free |
| Effort level | Low — check the trays once a week |
On this page
- Chitting potatoes at a glance
- Why chit potatoes, and what do you actually gain?
- When should you start chitting potatoes?
- Zone chart: when to start chitting in USDA zones 3–6
- Light and temperature: why chits turn short and green
- How to chit potatoes step by step
- How many sprouts should you keep?
- Should you cut seed potatoes before planting?
- Which potato varieties benefit most from chitting?
- Troubleshooting: what the sprouts are telling you
- Chitting in soil: the version that grows roots too
- Planting chitted potatoes without snapping the shoots
- When is chitting not worth it?
- Common mistakes
- Frequently asked questions
Why chit potatoes, and what do you actually gain?
A seed potato dropped straight into cold spring soil does nothing for a surprisingly long time. It first has to break dormancy, then push sprouts, then grow roots — all of it in ground sitting at 7 or 8 °C (45–46 °F). That takes weeks. A chitted tuber has already done the first two steps in your kitchen at room temperature, so everything it does underground goes into roots.
The clearest evidence is in emergence. Trials on greensprouted seed found 87 to 96 percent of chitted plants up by day 18, against 21 to 37 percent of unchitted seed — the difference between an even stand and a row full of gaps.
Four things you actually gain
- An earlier harvest. Count on 10–14 days in a normal season. Commercial greensprouters report gaining "about 10 to 14 days on the season", and seed suppliers put it at up to two weeks.
- More tubers per plant. Chitted seed generally sets more tubers per hill, because several sprouts start together and the plant gets a longer tuber-bulking window.
- Less seed rot. The shorter a tuber sits inert in cold wet soil, the less chance rot organisms get. Fast emergence is a disease control measure.
- A free quality check. A tuber that refuses to sprout in four weeks of warmth and light will not sprout in the ground either. You cull it on the kitchen table instead of finding a gap in the row in June.
What chitting does not do
It does not rescue poor seed, cure virus or blight, or add much to total yield if you are lifting in autumn anyway. The gain is in time, not in pounds. For what does move the yield needle — soil prep, hilling, watering and variety choice — see the guide to how to grow potatoes.
When should you start chitting potatoes?
Always count backwards from your planting date, never forwards from a calendar date you read somewhere:
Start date = planned planting date minus 4 weeks.
The workable range is three to six weeks, and four is the safe middle. Six weeks only works if you can hold the temperature genuinely low, otherwise the sprouts overshoot.
Why starting earlier backfires
The tempting mistake is to buy seed as soon as it appears in the shops and start immediately, on the theory that earlier is better. It is not. A tuber chitted for ten weeks either carries long brittle shoots that break at planting, or has poured so much of its reserve into those shoots that it shrivels and has nothing left to fuel the young plant. In a warm dry room, sprouts can even set tiny tubers directly on the seed piece — at which point the advantage is spent.
If you buy early, hold the tubers cold and dark at 4–6 °C (40–43 °F) until it is time. A crisper drawer or an unheated cellar works; they sit in dormancy and wait.
What sets the planting date?
Potatoes go in when soil at 10 cm (4 in) depth has warmed past roughly 7–10 °C (45–50 °F), which in most cold-climate gardens falls two to four weeks before the average last frost. Frost still matters, because potato foliage is killed at a couple of degrees below freezing. The full breakdown of soil temperature, frost dates and how to tell when your ground is genuinely ready is in the guide to when to plant potatoes.
Zone chart: when to start chitting in USDA zones 3–6
Guide dates for an average year. Adjust for the weather, for row cover or low tunnels, and for your own site — a south-facing sandy slope warms weeks ahead of a clay hollow in the same township.
| USDA zone | Typical areas | Average last frost | Plant potatoes | Start chitting | First earlies ready |
|---|---|---|---|---|---|
| 3 | Northern Minnesota, North Dakota, interior Canadian prairies, northern Scandinavia | Mid-May to early June | May 10–30 | April 12–May 2 | Late July |
| 4 | Central Minnesota, Vermont, northern Maine, southern Ontario interior | May 10–20 | April 25–May 15 | March 28–April 17 | Early to mid July |
| 5 | Southern Michigan, Iowa, upstate New York, southern Ontario lakeshore | April 30–May 15 | April 10–30 | March 13–April 2 | Late June |
| 6 | Pennsylvania, Ohio, coastal New England, central Scotland | April 15–30 | March 25–April 15 | February 25–March 18 | Early to mid June |
| Maritime mild (UK, Ireland, coastal Scotland) | Frost-free coastal belts | Late March to mid April | Late March for first earlies | Late January to early February | Late June |
One thing is worth reading out of that table: chitting matters more the colder the zone, not less. In zone 6 two weeks is a bonus. In zone 3 it is often the difference between full-sized tubers and marbles when the first hard frost arrives in late August. The zone 3 and 4 start dates also land in April, when spring sun through glass is strong — a bright but cool room beats a sunny one.
Light and temperature: why chits turn short and green
A potato sprout growing in darkness stretches. The tuber is searching for light, so it spends everything on length: the shoot comes out white or pale yellow, pencil-thin, and so brittle it snaps when you lift the tuber. That is etiolated growth — the same process that turns a seedling on a dark shelf into a pale thread.
Give the same sprout light and something different happens. Elongation slows, the cells stay short and thick, chlorophyll forms, and the sprout turns green, blue-green or purple depending on variety. Leaf and root initials develop at its base at the same time. That is the chit you want: a stubby, finger-thick bud that survives handling and carries on growing the day it hits soil.
The two-stage temperature routine
Most advice says "cool and light" and stops there. It works better in two stages.
| Stage | Temperature | Light | Duration | What happens |
|---|---|---|---|---|
| 1. Wake-up | 18–21 °C (65–70 °F) | Not critical | 5–10 days | Dormancy breaks, eyes swell, first sprout tips appear |
| 2. Greening | 10–13 °C (50–55 °F) | As bright as possible | Remaining weeks | Sprouts stay short, thicken and colour up green or purple |
| Holding gear (if needed) | 4–8 °C (40–46 °F) | Bright | While planting is delayed | Sprout growth almost stops without damage |
The wake-up stage matters most when seed has come straight out of cold storage with no sprouts showing. If your tubers already have visible sprout tips at purchase, skip stage one.
The holding gear is the most useful line in the table. Spring turns cold and planting slips two weeks? Move the trays to a porch at around 5 °C (41 °F), bright and frost free. The sprouts essentially pause, and you sidestep the classic problem of seed that got away from you.
How bright is bright enough?
Ordinary daylight in a room with a window is plenty, and a north-facing sill is ideal. A south window works too, but drape newspaper or thin cloth over the trays through the middle of the day — direct sun through glass leaves tubers hot and dehydrated. With no bright cool room at all, a basic grow light or a shop LED tube over the trays for twelve hours a day does the job. It is the same principle that decides whether transplants come out stocky or leggy when you sow tomato seeds: light quantity, not warmth, controls stretch.
How to chit potatoes step by step
- Buy certified seed potatoes. Use seed sold for planting, not table potatoes. Certified seed is inspected for virus and quarantine diseases such as ring rot and potato wart, and supermarket stock is often treated with a sprout inhibitor.
- Get the tubers out of the bag immediately. A closed sack is damp and dark, which is where both rot and long white shoots begin.
- Sort them. Discard anything soft, foul-smelling, deeply pitted or badly shrivelled. Tubers of 40–80 g (1.5–3 oz), about hen's-egg size, are ideal as they are.
- Wake them up. Hold at 18–21 °C (65–70 °F) for five to ten days until the eyes swell. Skip this if sprout tips are already showing.
- Set them out one layer deep in egg cartons, seed trays or a shallow fruit box. Tubers should not touch or stack.
- Point the rose end up. The rose end is furthest from the small scar where the tuber joined the stolon, and it is where the eyes cluster. The scarred heel end goes down.
- Move them somewhere bright and cool: 10–13 °C (50–55 °F), as much daylight as you can give, no scorching sun, frost free at all times.
- Check weekly and rotate the tray to even out the light. Pull any tuber going soft before it infects its neighbours.
- Rub off the weakest sprouts. Once sprouts are a few millimetres long and you can see which are strongest, pinch off the spindly ones and leave three or four sturdy ones. Details below.
- Plant at 1–2.5 cm (1/2–1 in) of sprout, short, thick and coloured. If bad weather has pushed them past 3 cm (11/4 in), drop the temperature rather than break them off.
How many sprouts should you keep?
Every sprout becomes a stem, and every stem forms its own stolons and tubers. Many stems give many small tubers; few stems give fewer, larger ones. Total weight moves surprisingly little — what you adjust is size distribution.
| Sprouts left on the tuber | Result | Best for |
|---|---|---|
| 1–2 | Fewer but clearly larger tubers, slightly later | Baking potatoes, big russets |
| 3–4 | Balanced — a good count at a useful size | The default for almost everyone |
| 5 or more | Many small tubers, fast and even emergence | New potatoes, fingerlings, bags and containers |
The standard advice is to keep three or four and rub the rest off — the traditional instruction to "remove all but three or four of the eyes". It gives a plant that can support its stems, at the size most people want.
How to do it
Wait until sprouts are a few millimetres to a centimetre long so you can tell which are strongest, then rub the weak ones off with your thumb. A small damp patch where a sprout was is fine; it dries over within a day. Where you have a choice, keep sprouts spread over the tuber rather than four crowded together at the rose end.
The one thing not to do
Never strip every sprout off a tuber. While the main sprouts are present they suppress the dormant eyes — the same apical dominance that makes an unpruned shrub grow up instead of out. Remove all of them and the tuber starts a fresh set of eyes from scratch, costing a couple of weeks. It usually happens by accident, when somebody "tidies up" a leggy tuber by pulling all the shoots off.
Should you cut seed potatoes before planting?
A seed potato of 40–80 g (1.5–3 oz) is planted whole — it carries about the right reserve to drive the sprouts until the plant supports itself. Noticeably larger tubers, say over 100 g (3.5 oz), can be cut to double the number of plants you get from a bag.
How to cut seed potatoes
- Chit the tuber whole first. That way you can see where the eyes are and which sprouts came out strongest.
- Cut one to two days before planting, not weeks ahead.
- Use a clean sharp knife and cut into blocky pieces of 40–60 g (1.5–2 oz), each with at least one well-developed eye or sprout — two is better.
- Let the cut faces sit in a humid, airy spot at room temperature for two to three days so the surfaces suberize and form a corky protective layer.
- Plant cut side down or sideways, never facing up.
When not to cut
Do not cut if the soil will be cold and wet at planting. A raw cut face in 7 °C (45 °F) saturated ground is an open door for rot. In zones 3 and 4, and in any wet spring, whole seed is the safe choice. Do not cut small tubers just to get more plants either — a 20 g (3/4 oz) piece makes a weak plant that never catches up.
Which potato varieties benefit most from chitting?
Any variety can be chitted, but the payoff is unevenly spread. The rule of thumb: the earlier the variety, the more you gain.
First earlies — this is where the whole gain sits
First earlies are lifted as new potatoes while the tops are still green, so every day counts, and two weeks can decide whether you dig in June or July. Varieties in this group include 'Rocket', 'Swift', 'Arran Pilot', 'Pentland Javelin' and 'Red Norland'.
Second earlies — usually worth it
Second earlies and early maincrops such as 'Charlotte', 'Yukon Gold' and 'Kennebec' also respond, especially in zones 3 and 4. Here the benefit is less about a June harvest and more about tubers finishing before frost takes the foliage.
Maincrop — generally not worth the windowsill
Late maincrops grown for storage, such as 'King Edward', 'Maris Piper', 'Desiree' and 'Russet Burbank', grow over a long period and get lifted when the haulm dies down regardless. The Royal Horticultural Society states plainly that there is no real advantage to chitting maincrops. It does no harm, but give the bright cool space to the earlies first.
The short-season exception
The further north you garden, the more that line blurs. In zone 3, chitting a second early can be what makes it viable at all — though the better answer there is usually to choose a genuinely early variety instead.
Troubleshooting: what the sprouts are telling you
Look at the trays once a week. The sprouts report fairly precisely on what is wrong.
| What you see | What it means | What to do |
|---|---|---|
| Long, white, thin, brittle shoots | Too dark, usually combined with too warm | Move into light immediately. Shoots green up but never shorten — plan to plant them gently |
| No sprouts at all after three weeks | Too cold, or the tuber is still in deep dormancy | Raise to 18–21 °C (65–70 °F) for a week. If nothing happens, the tuber is spent |
| Sprouts over 5 cm (2 in) and planting is still weeks away | Too warm, or started too early | Drop to 4–8 °C (40–46 °F), keep the light. Do not snap the sprouts off |
| Tuber shrivelling, soft and wrinkled | Too warm and too dry — it is consuming its own water | Lower the temperature. A slightly wrinkled tuber still plants; a soft one does not |
| Tiny tubers forming directly on the sprouts | Heat stress, usually after a warm spell | Plant it now. The head start is gone but the plant is usually fine |
| Dark sunken patches with a rotten smell | Soft rot or dry rot | Bin the tuber. Do not handle healthy tubers afterwards without washing your hands |
| White or grey fuzz on the surface | Mould from damp, crowded conditions | Spread the tubers out, improve airflow, wipe the surface |
| Green skin over the whole tuber | Entirely normal for chitted seed | No action. This tuber gets planted, not eaten |
If the shoots got long anyway
It happens to everyone, and the seed is not wasted. A tuber with 10 cm (4 in) pale shoots still crops, but handle it carefully: lay it in the furrow with the shoots pointing along the row rather than standing them upright, and draw soil over them without pressing down. They bend upward on their own within a week.
Chitting in soil: the version that grows roots too
There is a heavier version worth knowing if you are chasing the earliest possible new potatoes: sprout the tubers in moist soil rather than on a dry tray.
Put a couple of centimetres (1 in) of moist potting mix in a shallow tray, press the tubers in loosely rose end up, and scatter a thin layer around them without burying the sprouts. Keep it bright at 12–15 °C (54–59 °F). The tuber then forms roots as well as sprouts, so the plant has a root system from day one.
The upside is a few more days of head start. The downside is that the tuber becomes fragile to move — roots tear easily — and it is now effectively a tender transplant. The method suits grow bags, containers and greenhouse beds, or rows under cover. Start a chitted tuber in a 10-litre (2.5 US gal) pot in a greenhouse in early spring and you can dig new potatoes weeks before the outdoor rows emerge.
Planting chitted potatoes without snapping the shoots
Four weeks of carefully chitting potatoes can be undone in ten minutes of rough handling.
- Carry the tubers in the tray they chitted in. A bucket of chitted seed sounds satisfying and arrives full of broken sprouts.
- Dig the trench first. Have trench, compost and spade ready before the potatoes come outside.
- Place, do not press. Set each tuber in the trench sprouts up and leave it. Do not push it down into the soil with your palm.
- Cover with loose soil. Planting depth is normally 10–15 cm (4–6 in) measured to the top of the tuber.
- Have row cover ready. Chitted seed emerges faster, so the foliage meets frost risk earlier. In zones 3 to 5 a late frost after emergence is the rule, and fleece over the row costs almost nothing.
When is chitting not worth it?
Chitting is optional, and in some situations it is wasted effort.
- Maincrop for storage. You lift when the haulm dies in autumn regardless, so the two weeks disappear at the far end.
- No bright cool space. Chitting in warm darkness is worse than not chitting at all, because you end up planting tubers with fragile shoots.
- Large plantings. Fifty kilos (110 lb) of seed takes real floor space in a lit room. Prioritise the earlies.
- You are already late. If it is mid-May in zone 5, the potatoes belong in the ground, not in an egg carton. Plant unchitted rather than adding three more weeks.
Everywhere else — especially for first earlies — the answer is yes. It fits neatly into spring planning too: the potato bed wants attention early, while how to grow carrots can wait for warmer soil and how to grow garlic was settled back in October.
Common mistakes
- Chitting in the dark. The single most common error. Basements, closets and windowless garages produce long white shoots that break at planting. Light is not optional — it is the entire point.
- Starting too early. Ten weeks in an egg carton gives shrivelled tubers and overgrown sprouts.
- Running it too warm. Above 18 °C (65 °F) throughout gives fast but weak growth. After the wake-up stage, tubers belong at 10–13 °C (50–55 °F).
- Leaving the seed in the bag. Damp, dark and airless in one package.
- Rubbing off every sprout. Apical dominance lifts, the tuber restarts from scratch and you lose weeks. Remove the spindly ones, keep three or four.
- Forgetting frost. One cold night on an unheated porch can cost the whole tray.
- Cutting seed weeks in advance. Cut faces dry the tuber out or invite rot. Cut a day or two ahead and let the surfaces cork over.
- Using grocery-store potatoes as seed. Often treated with a sprout inhibitor, never inspected for virus or quarantine disease. Buy certified seed.
Frequently asked questions
How long does chitting potatoes take?
Three to six weeks, with four weeks as the standard. Under three weeks the sprouts do not have time to thicken usefully, and beyond six they tend to overshoot unless you are holding them genuinely cool. The planting date always drives it: decide when the potatoes go in the ground, then count back four weeks and start then.
Should potatoes be chitted in light or in the dark?
In light, always. Light is what makes sprouts short, thick and green instead of long, white and brittle. A bright room or a windowsill out of scorching sun is plenty. Chitting in darkness produces etiolated shoots that snap the moment you lift the tuber, which costs you exactly the head start you were trying to build.
What temperature should seed potatoes be chitted at?
Start at 18–21 °C (65–70 °F) for five to ten days to break dormancy, then move the tubers to 10–13 °C (50–55 °F) in bright light for the rest of the time. If planting is delayed, drop to 4–8 °C (40–46 °F), which nearly stops sprout growth without harming the seed. Keep everything frost free throughout.
How long should the chits be before planting?
Aim for 1–2.5 cm (1/2–1 in). Sprouts should be thick, compact and green or purple, not thread-like. Longer than 3 cm (11/4 in) is still plantable, but handle the tubers gently and lay them in the trench rather than pressing them in. Never break long sprouts off to tidy them up.
How many sprouts should you leave on a seed potato?
Three or four is the default and gives a good balance of number and size. For fewer, larger baking potatoes keep one or two. For lots of small new potatoes leave five or more. The one thing to avoid is removing every sprout, because that releases apical dominance, the tuber starts over from dormant eyes and you lose a couple of weeks.
Can you chit potatoes in an egg carton?
Yes, and it is the most common method for good reason: the carton holds each tuber upright with the rose end up, keeps tubers from touching, and lets air reach all sides. A seed tray, moulded paper flat or shallow fruit box works just as well. What does not work is leaving the seed in the sack it came in.
Does chitting really make potatoes crop earlier?
Yes — count on 10 to 14 days in an average season. The gain comes from much faster emergence: trials recorded 87 to 96 percent of greensprouted plants up by day 18 against 21 to 37 percent of unsprouted seed. Total yield rises only modestly, so think of chitting as buying time rather than adding pounds.
Can you eat a potato that turned green while chitting?
No. The green is chlorophyll, which is harmless in itself, but it signals that the tuber has also been making glycoalkaloids such as solanine — and sprouts carry the highest concentrations of all. A chitted seed potato is planting stock and belongs in the ground. The same warning applies to any table potato that has been left in the light and greened.
Want more grow guides like this straight to your inbox — sign up for the GardenLovers newsletter and get each season's reminders before the planting window closes.