When to Plant Seed Potatoes: First Earlies to Maincrop

The short version: chit your seed potatoes from late January, plant first earlies in mid to late March, second earlies in early April, and maincrop from mid to late April, always two to three weeks after your last expected frost in your area. Dates matter less than soil temperature, and most people plant two to three weeks too early because they're impatient, not because the soil is ready.

I am not a gardener by trade. I write about business and AI for a living. But I grow vegetables on a scrap of allotment-sized ground because staring at a spreadsheet all day makes me want to put my hands in soil, and potatoes are the crop that teaches you patience faster than anything else you'll grow. So this post is me doing what I do with everything else: reading the actual guidance, ignoring the vague bits, and giving you numbers you can use.

The three categories, and why the names are confusing

Seed potato suppliers split varieties into first earlies, second earlies, and maincrop. The names refer to how long the plant takes from planting to harvest, not to when you plant them. All three can go in the ground within a few weeks of each other. What differs is when you lift them.

• First earlies (Rocket, Swift, Pentland Javelin, Casablanca) take 10 to 12 weeks and give you small new potatoes for summer salads.
• Second earlies (Charlotte, Kestrel, Nadine) take 13 to 16 weeks and bridge the gap between new potatoes and storage crops.
• Maincrop (Maris Piper, King Edward, Desiree, Rooster) take 20 weeks or more and are the ones you store through winter.

Chitting: the step people skip and then wonder why their crop is late

Chitting means standing your seed potatoes rose end up (the end with the most eyes) in a cool, bright, frost-free spot for four to six weeks before planting, so they grow short, sturdy green shoots about 2cm long. An egg box or seed tray on a windowsill does the job.

Chitting isn't essential. You can plant unchitted potatoes and they'll still grow. But chitted first earlies crop roughly two weeks earlier than unchitted ones, which matters if you're racing to beat blight or just want new potatoes before everyone else's are ready. Maincrop varieties benefit less from chitting because they're in the ground long enough to catch up regardless.

Start chitting in late January if you're in the UK, so your seed potatoes are ready to go in by mid to late March.

Planting dates by category

These are UK-centred because that's where most seed potato suppliers and most of my readers who grow veg are based, but the logic transfers anywhere with a frost line. Adjust by your own last frost date.

• First earlies: plant mid to late March, roughly 10cm deep, 30cm apart, rows 45cm apart.
• Second earlies: plant early to mid April, same depth, 35cm apart.
• Maincrop: plant mid to late April, 40cm apart, rows 75cm apart because the foliage gets huge and needs room.

If you garden somewhere colder, in the north of Scotland or at altitude, push everything back two to three weeks. If you're in a mild southern or coastal spot, you can plant a week or two earlier without much risk.

The soil temperature rule that matters more than the calendar

Here's the bit most potato guides gloss over. Seed potatoes don't care what the date is. They care what the soil temperature is. They want soil at a minimum of 7 to 8 degrees Celsius before they'll put on decent growth, and ideally warmer than that. Push a thermometer into the ground at planting depth for a few mornings in a row. If it's reading 5 degrees, planting on the "correct" date on a chart won't help you. The seed will sit there sulking, rotting in cold wet ground, rather than growing.

This is the uncomfortable bit nobody likes to say out loud: most allotment forums are full of people who planted on the first warm weekend in March because the calendar told them to, then spent April complaining that half their first earlies rotted. The calendar is a guide. The soil thermometer is the actual instruction.

Worked example: planning a plot with all three types

Say you run a small allotment plot and want new potatoes by June, a salad crop by midsummer, and a store of maincrop for roasting through winter. Here's how the timeline would realistically look, assuming a UK last frost date of mid April and reasonably average soil:

• Late January: buy seed potatoes, start chitting first earlies and second earlies on a windowsill.
• Mid March: check soil temperature weekly from the 1st. Once it holds above 7 degrees for several days, plant first earlies (say, 20 March).
• Early April: plant second earlies once soil is reliably warmer, around 5 to 10 April.
• Mid to late April: plant maincrop, around 20 to 25 April, once the last frost risk has passed.
• Late May to early June: earth up all rows as shoots reach 20cm, covering all but the top few centimetres to protect against late frost and encourage more tubers.
• Mid to late June: lift first earlies when flowers open, test one plant first by digging gently at the edge of the row.
• August: lift second earlies.
• September to early October: lift maincrop once the foliage has died back, leave tubers in the ground for two weeks after cutting back the haulms to let skins toughen for storage.

That's a six-month operation from a few quid spent on seed potatoes and an egg box. It's also a decent reminder that most worthwhile things, whether it's a potato crop or a client pipeline, run on a sequence, not a single date.

Frost risk and earthing up

Even after your last frost date, a late frost can still catch emerging shoots. Earthing up, mounding soil over the row as shoots appear, protects against this and also stops tubers near the surface turning green (green potatoes contain solanine and shouldn't be eaten). If frost is forecast after planting and shoots have emerged, cover them with fleece or extra soil overnight. Losing the top growth to frost won't kill the plant outright, it will just set it back and delay your harvest by a couple of weeks.

Container growing changes the dates slightly

If you're growing in a bag or large pot on a patio rather than open ground, you can plant two to three weeks earlier than the open-ground dates above, because you can move containers into a greenhouse, porch or against a south-facing wall overnight if frost threatens. This is the easiest route if you've only got a balcony, and first earlies in particular do very well in a 30-litre bag with three or four seed potatoes.

Storage and why maincrop timing affects how long potatoes last

Maincrop potatoes lifted too early, before the foliage has died back, store badly and shrivel within weeks. Potatoes lifted at the right time, skins cured for a fortnight in a dark airy spot, and stored in hessian or paper sacks (never plastic, which traps moisture and causes rot) in a cool dark place around 7 to 10 degrees, will keep for four to six months. That's the difference between eating your own potatoes at Christmas and throwing out a sack of mush in November.

Frequently asked questions

Can I plant seed potatoes too early?

Yes, and it's the most common mistake. Planting into cold, wet soil below 7 degrees Celsius leads to rot rather than growth, so check soil temperature rather than relying purely on a calendar date.

Do I need to chit seed potatoes before planting?

No, it isn't essential, but chitting first and second earlies for four to six weeks before planting typically brings your harvest forward by around two weeks, which matters more for earlies than for maincrop.

What's the difference between first earlies, second earlies and maincrop?

The difference is time to harvest, not planting date. First earlies take 10 to 12 weeks and give small new potatoes, second earlies take 13 to 16 weeks, and maincrop takes 20 weeks or more and is what you store through winter.

How deep and how far apart should I plant seed potatoes?

Plant around 10cm deep, spacing first earlies 30cm apart, second earlies 35cm apart, and maincrop 40cm apart, with wider rows for maincrop since the foliage spreads further.