How to sow tomato seeds in the UK
Updated: 16 October 2026
You have a packet, or you are about to sow, and you need a month and a temperature that suit a British spring. How to sow tomato seeds comes down to two calendars that do not match, then to the depth on your packet. Packets and prices are on the [tomato seeds comparison](/hub/herb-seeds/tomato-seeds). This page does not rank them. The dates below come from the RHS tomato guide and Gardeners' World on 23 May 2025, plus the sowing lines on these listings, read on 15 October 2026. There is no single UK frost date here.
You have a packet, or you are about to sow, and you need a month and a temperature that suit a British spring. How to sow tomato seeds comes down to two calendars that do not match, then to the depth on your packet.
You have a packet, or you are about to sow, and you need a month and a temperature that suit a British spring. How to sow tomato seeds comes down to two calendars that do not match, then to the depth on your packet. Packets and prices are on the tomato seeds comparison. This page does not rank them. The dates below come from the RHS tomato guide and Gardeners' World on 23 May 2025, plus the sowing lines on these listings, read on 15 October 2026. There is no single UK frost date here.
Our top picks
| Badge | Product | Sowing note | Habit on listing | Stated seed count | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Just Seed Just Seed Sungold F1 tomato seeds | Not stated | Not stated | 10 | 9.5 | about £3.65 | View offer |
| Best value |  Just Seed JustSeed Moneymaker tomato seeds | Not stated | Not stated | 100 | 9.3 | about £2.75 | View offer |
| Alternative |  Meldon Seeds Meldon Moneymaker tomato seeds | 0.5 cm deep, 18–21°C | Indeterminate | 18 | 9.3 | about £2.95 | View offer |
On this page
Two UK calendars, not one
The RHS says sow from late February to mid-March for a greenhouse crop, and from late March to early April if the plants will live outside. Gardeners' World starts earlier indoors: from early February in the house or a greenhouse, and from March to early April for outdoor crops. Pick one calendar and keep to it.
Outdoor plants are sown later because they cannot go out until the frost risk has passed. If you have no greenhouse, use that later window. Where the crop will stand is on greenhouse or outdoor tomatoes. When the packet prints no month, the guide supplies the month and the packet supplies the depth and the heat.
Heat, cover and light
Both guides specify a peat-free compost. The RHS gives about 18°C. Cover the tray with a lid or a clear bag, and take it off once seedlings show, which the RHS says is usually within a fortnight. After that they need light. A warm, dim windowsill produces the long pale stem people call leggy.
Gardeners' World says water from below, so the surface stays drier and damping off is less likely. Meldon's bullets say a propagator at 18–21°C, which sits beside the RHS figure rather than against it. A kitchen that falls to 14°C at night will not behave like a propagator set near 20°C.
When the packet prints a different number
Use the packet's depth and temperature when it prints them. Do not average it with a magazine. Meldon's Moneymaker and Ailsa Craig say 0.5 cm at 18–21°C. The Seeds & Spice kit says 22–28°C over 8–21 days. Mar Azul and Montserrat say 20–28°C and 5–10 days. If that is the packet you bought, follow that range.
San Marzano's care line says 1 inch deep and 6 inches apart. One inch is much deeper than 0.5 cm. Bury each seed as that packet says. Black Cherry's material line says germination in 15 days and gives no temperature. Where the packet is silent, use about 18°C, and treat 15 days as the seller's claim. If the listing never says cordon or bush, use the tomato seeds buying guide first.
Pricking out and the wait
The RHS says prick out at two true leaves, holding a leaf rather than the stem. A leggy seedling can be replanted deeper, and afterwards you keep at least 16°C. Gardeners' World moves them into 8 cm pots.
Spacing depends on the guide you opened. The RHS says 45–60 cm in the ground, one plant in a 30–45 cm pot, and two in a standard grow-bag. Meldon says three per grow-bag once the plants are 20 cm high. Use the seller's three for that packet. They go outside after frost. Gardeners' World puts that, usually, in May, after a couple of weeks of hardening off. Side-shoots belong only on cordons, and only once you know the habit.
What a failed tray does not prove
Reviews on several of these listings say nothing came up, and other reviews on the same listing say every seed did. Ailsa Craig's file includes a total miss and 12 germinated from 40 sown. JustSeed Moneymaker has a no-germination review beside a 4.4 star line. That pattern is one tray, not a brand germination rate, and it is not a sowing method you should copy. A cold sill, a sodden tray and a poor packet can look the same from above.
Check the temperature you held and the depth that packet printed before you blame the variety. Then decide whether you need another packet, rather than sowing a contradictory listing deeper.
Common questions
When do I sow tomato seeds in the UK for a greenhouse?
Follow one named calendar. The RHS says late February to mid-March for plants that will grow under glass. Gardeners' World says from early February indoors or in a greenhouse. Both assume heat around germination temperature, not a cold January sill. The packet usually does not print the month, so the guide supplies it.
When do I sow if the plants will live outside?
Later than a greenhouse crop. The RHS says late March to early April for plants that will live outside. Gardeners' World says March to early April. The seed still germinates indoors. An early February sowing only leaves you housing large plants through a cold April.
What temperature do the seeds need?
The RHS says about 18°C. Meldon prints 18–21°C. The kit prints 22–28°C, and Mar Azul and Montserrat print 20–28°C. Use the figure on your packet when it exists. If the packet is silent, use about 18°C rather than inventing a compromise between the guides.
How deep do I cover them?
Meldon says 0.5 cm. Gardeners' World says a thin cover, which is the same idea. San Marzano's care line says 1 inch, which is far deeper. Cover each packet as that packet says. A missing depth is not a reason to borrow another brand's number.
Why are my seedlings long and pale?
They are short of light, often on a warm windowsill with the cover left on. The RHS expects seedlings within about a fortnight, then the cover off and good light, with at least 16°C after pricking out. You can replant a leggy seedling deeper. You cannot feed it into a stocky plant.
When can they go outside?
After frost, and after hardening off. Gardeners' World puts planting out, usually, in May, after a couple of weeks of hardening off. The RHS wants conditions reliably above 16°C. A packet that says outdoors above 12°C is stating its own line. It does not replace the guide you chose for the British planting date.
Related pages
Sources
Public UK sources named for this comparison. Listings read on 15 October 2026.
- RHS, How to grow tomatoes (retrieved October 2026)
- RHS, Tomato blight (retrieved October 2026)
- Gardeners' World, How to grow tomatoes (23 May 2025) (retrieved October 2026)
- Seed Marketing Regulations 2011, Schedule 3 (retrieved October 2026)
- GOV.UK, Plant breeders' rights (retrieved October 2026)
- amazon.co.uk listings for the eleven packets, read 15 October 2026 (retrieved 15 October 2026)