Seed Sowing Month by Month UK Guide
This month-by-month seed sowing calendar covers over 60 varieties of vegetables, fruits, and flowers for UK gardeners. We have drawn on 16 years of greenhouse installation experience to compile accurate sowing times for every season. The guide includes greenhouse and outdoor sowing dates from January through December. Sowing starts as early as January with chillies and sweet peas in a heated greenhouse or warm windowsill.
Key Takeaways
- Start in January – sow chillies and sweet peas in a heated greenhouse or warm windowsill
- March is the busiest month – carrots, parsnips, beetroot, and first early potatoes all go in
- Succession sow salads – sow every 2–3 weeks from April for continuous harvests
- Plan autumn crops in July – kale, winter cabbage, and brassicas need sowing mid-summer
- Greenhouses extend your season – start 4–6 weeks earlier and grow 4–6 weeks later than outdoors
Installer's Note
Customers often ask what they can start growing straight away after a greenhouse installation. Even in January, a new greenhouse gives you a 4–6 week head start on outdoor sowing. We have fitted greenhouses in every month of the year. Every single time, the owner has something they can sow that same week.
January: Getting a Head Start
January is quieter, but it is the perfect time to get ahead of the season. In a heated greenhouse or on a warm windowsill, sow chillies at 20–25°C for best germination. We have found that starting chillies this early gives the long growing season they need. Read our full guide to growing chillies in a greenhouse for detailed advice.
Microgreens are another excellent January crop. They germinate in 5–7 days and are ready to harvest in under three weeks. Sweet peas and snapdragons can also go in now for strong root systems before spring planting.
February: Preparing for Spring
February is when we start the main warm-season crops indoors. Sow tomatoes, peppers, and aubergines in a heated propagator at 18–22°C. These need 6–8 weeks of indoor growing before they are ready to transplant.
Broad beans and peas can go into an unheated greenhouse or cold frame this month. For flowers, start geraniums and chrysanthemums on a bright windowsill. Good ventilation is important to prevent damping off in seedlings.
March: The Busiest Month
March is when outdoor sowing begins in earnest. Carrots, parsnips, and beetroot can go directly into prepared beds. Plant first early potatoes 10–15cm deep with 30cm spacing between tubers.
In the greenhouse, start growing tomatoes in a greenhouse if you did not sow in February. Cosmos, cornflowers, and marigolds can be sown directly outdoors. Protect early sowings with fleece or cloches if frost is forecast.
April: Full Speed
April is one of the busiest months in the gardening year. Most vegetables can now go directly outdoors. Sow peas, carrots, beetroot, lettuce, and radishes in succession for continuous harvests.
Plant maincrop potatoes by mid-April. Start hardening off indoor-raised seedlings over 7–10 days before planting out. Tender crops like courgettes and squash can be started in the greenhouse for transplanting after the last frost.
Sunflowers and nasturtiums sown now will flower by midsummer. We recommend sowing salad leaves every 2–3 weeks from this month onwards.
May: Tender Crops Go Out
After the last frost date, usually late May in most of the UK, tender vegetables move outdoors. Sweetcorn, cucumbers, and pumpkins can be direct-sown or transplanted from the greenhouse.
Keep up with succession sowing of salad crops. Sow foxgloves and other biennials now for flowers next year. Watch for slugs on young plants and use organic pellets or copper tape around vulnerable seedlings.
June: Maintaining Momentum
June is about keeping the sowing cycle going. Continue succession sowings of radishes, lettuce, spring onions, and French beans. These quick-growing crops fill gaps left by harvested early vegetables.
Sow biennials and perennials for next year's flower display. Water consistently in warm weather. Seedlings dry out fast in a greenhouse, so check trays morning and evening during hot spells.
July: Planning for Autumn
While we enjoy summer harvests, July is when autumn and winter crops need sowing. Kale, winter cabbage, and other brassicas must go in now for harvests from October onwards. Net them straight away to protect against cabbage white butterflies.
This is your last chance for many summer crops. Sow wallflowers and sweet Williams for spring flowers next year. We find that customers who skip July sowings have a bare patch in their autumn and winter harvests.
August: Late Summer Sowings
August is the final window for many summer vegetables. Sow winter spinach, chard, and turnips for autumn harvests. Winter lettuce varieties go into the greenhouse for cropping through the colder months.
Hardy annuals sown now will flower earlier next spring than spring-sown ones. Keep harvesting courgettes, beans, and tomatoes regularly to encourage continued production.
September: Autumn Transition
September marks the shift to autumn gardening. Sow green manures like field beans or phacelia on cleared beds to improve soil over winter. This is one of the most useful things you can do for next year's crops.
Winter salads and spring cabbages go in now. Sow cornflowers and poppies outdoors for early spring colour. Start thinking about preparing your greenhouse for spring by cleaning glass and checking seals before winter sets in.
October: Planting for Next Year
October is mostly about setting up next year's growing season. Sow broad beans and overwintering peas for an early spring crop. Plant garlic cloves 5cm deep and 15cm apart.
In the flower garden, sow sweet peas in pots for strong plants next spring. Protect newly sown beds from early frosts with fleece. We always plant garlic on our own allotment in the first two weeks of October.
November: Overwintering Crops
November is quieter, but several important crops need planting. Put in overwintering onion sets and shallots before the ground gets too cold. Broad beans sown now will crop 2–3 weeks earlier than spring-sown ones.
In the greenhouse, sow winter salads for fresh leaves through December and January. Check out our guide on what to grow in a greenhouse in winter for more ideas. Mulch around fruit trees and bushes before the first hard frost.
December: The Quiet Month
December is traditionally garlic planting time if you missed October. Winter salads and microgreens keep the greenhouse productive. Sow sweet peas and antirrhinums in pots on a bright windowsill for a head start next spring.
This is also the time to plan next year's crop rotation. Review what worked and what did not. Order seeds early for the best variety selection. Even in the coldest month, there is always something to sow. Watch for greenhouse pest control issues like botrytis in damp winter conditions.
Matt's Tip: Label Everything
By April you will have 20 or more seed trays on the go. They all look identical once the seedlings emerge. Use waterproof plant labels and a permanent marker for every tray. Write the variety name and the sowing date. I have lost track of unlabelled trays more times than I care to admit.
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Seasonal Sowing Reference Table
Use this table to plan your full year of sowing. It covers vegetables, fruits, and flowers with sowing depths, spacing, and common pest issues for each month.
| Month | Vegetables | Fruits | Flowers | Sowing Depth (cm) | Spacing (cm) | Common Pests/Diseases | Gardening Tips |
|---|---|---|---|---|---|---|---|
| January | Chillies, microgreens, potatoes (indoors) | Rhubarb (crowns) | Sweet peas, snapdragons (indoors) | 1.0 | 30 | Aphids, damping off | Use a heated propagator for better germination |
| February | Aubergines, tomatoes, peppers (indoors) | Apple trees, pear trees (bare root) | Hardy perennials, chrysanthemums | 1.5 | 40 | Blight, whitefly | Ensure good ventilation to prevent damping off |
| March | Carrots, parsnips, beetroot, broad beans | Strawberries | Dahlias, cosmos, marigolds | 2.0 | 20 | Flea beetles, carrot fly | Use fleece or cloches to protect early sowings |
| April | Peas, carrots, beetroot, lettuce, radishes | Strawberries, melons (under cover) | Sunflowers, nasturtiums, zinnias | 2.0 | 30 | Pea weevil, slugs | Start hardening off plants sown indoors |
| May | Sweetcorn, cucumbers, courgettes, pumpkins | Strawberries, outdoor melons | Zinnias, foxgloves, petunias | 2.5 | 60 | Crown rot, powdery mildew | Plant out tender vegetables after last frost |
| June | Radishes, lettuce, spring onions, French beans | Strawberries (harvest) | Biennials (foxgloves, wallflowers) | 1.0 | 25 | Mildew, blackfly | Keep on top of weeding and watering |
| July | Kale, winter cabbage, carrots, spring onions | Strawberries (runners) | Wallflowers, sweet Williams, forget-me-nots | 0.5 | 45 | Aphids, cabbage white butterflies | Net brassicas to protect from pests |
| August | Winter salads, spinach, chard, turnips | Strawberries (remove runners) | Hardy annuals for spring | 1.0 | 15 | Slugs, caterpillars | Keep harvesting to encourage more growth |
| September | Winter salads, spring cabbages, onion sets | Strawberries (new plants) | Cornflowers, poppies, spring bulbs | 1.0 | 20 | Rust, mildew | Start clearing summer crops |
| October | Broad beans, garlic, overwintering peas | Apple trees, pear trees (bare root) | Sweet peas, crepis rubra, spring bulbs | 5.0 | 25 | Mice, birds | Protect crops from early frosts |
| November | Onions, shallots, garlic | Apple trees, pear trees (bare root) | Laurentia, delphinium, hardy annuals | 2.0 | 25 | Whitefly, neck rot | Mulch around fruit trees and bushes |
| December | Winter salads (indoors), microgreens | Rhubarb (force existing crowns) | Sweet peas, antirrhinums (indoors) | 2.0 | 15 | Botrytis, damping off | Plan next year's crop rotation |
Frequently Asked Questions
What temperature do seeds need to germinate?
Most seeds germinate best between 18–22°C. This varies by plant type. Cool-season crops like lettuce and peas germinate at lower temperatures, around 10–15°C. Warm-season crops such as tomatoes and peppers need a minimum of 18°C. A heated propagator gives you the most consistent results.
Do seeds need sunlight or warmth to germinate?
Most seeds need warmth rather than sunlight to germinate. Many actually germinate better in darkness. Once seedlings emerge, they need good light to grow strong and avoid becoming leggy. A few varieties, including lettuce, do need light exposure to trigger germination.
When can seedlings go outside in the UK?
Seedlings can move outside after the last frost, usually late April to May. The exact date varies by region. Northern areas may need to wait until late May. Harden off seedlings over 7–10 days first. Gradually increase their time outdoors before planting them in their final positions.
What temperature is too cold for seed germination?
Below 10°C is too cold for most seed germination. Some hardy crops like broad beans and peas can manage at lower temperatures. Warm-season crops such as tomatoes and peppers will not germinate below 15°C. Soil temperature matters more than air temperature for germination success.
When can I start sowing seeds in an unheated greenhouse?
You can start sowing in an unheated greenhouse from late February. Hardy crops like lettuce, spinach, and some brassicas can go in first. Tender plants should wait until March or April. An unheated greenhouse still offers 4–6 weeks of advantage over outdoor sowing.
What are the easiest seeds to grow for beginners?
Radishes, lettuce, peas, and sunflowers are the easiest for beginners. Radishes germinate in 3–5 days and are ready to harvest in 4 weeks. Lettuce and salad leaves grow quickly with minimal fuss. Peas are forgiving and produce well even in cooler conditions. We always recommend these four to new greenhouse owners.
Related Articles
- How to Grow Seeds in a Greenhouse
- How to Grow Herbs in Your Greenhouse
- How to Grow Strawberries in a Greenhouse
- 6 Essential Greenhouse Growing Tips for Beginners
- How to Grow Potatoes UK
Questions about seed sowing? Email us at info@greenhousestores.co.uk
