May Planting Calendar for Allotments: Week-by-Week Guide

Introduction

May is one of the most exciting months on the allotment calendar. As spring gathers pace, longer days and warmer nights create the perfect conditions for sowing, planting, and nurturing a wide array of vegetables, herbs, and flowers. Getting your timing right in May can set you up for a bountiful harvest throughout summer and into autumn. In this article, we’ll walk you through a detailed, week-by-week May planting calendar for allotments, helping you know exactly what to sow, plant out, and manage each week. Whether you’re a seasoned gardener or just starting your allotment journey, this guide will ensure your plot thrives all season long.

Why Follow a May Planting Calendar for Your Allotment?

• Climatic Precision: Weather in May can still be unpredictable. A calendar tailored to early, mid, and late May helps you match tasks to soil temperature and frost risk.
• Maximize Yield: Staggering sowings and plantings over the month leads to a steady stream of produce rather than an overwhelming glut all at once.
• Pest and Disease Management: Timing sowings and plantings correctly minimizes exposure to pests and disease hotspots.
• Efficient Space Use: A week-by-week plan allows you to rotate crops and interplant effectively, reducing bare soil and boosting biodiversity.

How to Use This Week-by-Week Guide

1. Mark Your Calendar: Note the date ranges for each “week” and align them to your local frost dates.
2. Prepare in Advance: Soak seeds that benefit from pre-soaking and compost your plot in March–April to be ready for May.
3. Adjust for Microclimate: South-facing plots warm up sooner—move tasks earlier; north-facing or exposed plots may need a slight delay.
4. Record and Reflect: Keep a simple diary of sowing dates, germination success, and harvest timelines to refine next year’s schedule.

Week 1 (May 1–7): Early-May Sowing & Planting

Soil Preparation and Final Frost Check

• Soil Temperature: Aim for at least 10 °C (50 °F) for hardy vegetables; use a soil thermometer.
• Last Frost Date: In many UK regions, the last frost falls in early May. Hold off on tender crops until you’re frost-safe.

Sowing Directly Outdoors

• Peas & Broad Beans: Sow in trenches or double rows. Support peas with canes or netting.
• Carrots & Parsnips: Sow thinly in drills; use fine compost on top to prevent birds from disturbing seed.
• Onions: Plant onion sets 10 cm apart, in rows 30 cm apart.
• Radishes: Sow succession plantings every fortnight for continuous harvest.

Under Cover (Cold Frame/Cloche)

• Courgettes & Pumpkins: Sow in modules under cloches or cold frames; they need 15 °C+ to germinate.
• Tomatoes & Peppers: If not already pricked out, transplant into individual pots and keep in a greenhouse or heated propagator at 18–20 °C.

Soil Improvement & Weeding

• Green Manures: If any beds remain fallow, sow a fast-growing mustard or buckwheat to smother weeds and add organic matter.
• Weed Control: Hoe between rows in warm, dry weather to reduce weed competition.

Week 2 (May 8–14): Harden-Off & Continued Sowing

Hardening Off Seedlings

• Acclimatize Tender Crops: Move young plants like courgettes, tomatoes, and peppers outdoors for increasing periods, sheltered from wind.

Direct Sow Successions

• Lettuces & Leafy Salads: Sow every 2–3 weeks; use shade cloth on hot days to prevent bolting.
• Beans: Sow dwarf and climbing beans outdoors now soil temps are reliably above 12 °C. Plant dwarf beans 10 cm apart, climbing beans 30 cm apart.
• Beetroot: Sow in drills; thin to 10 cm once true leaves develop.

Plant Out

• Brassicas: If protected from caterpillars (e.g., with mesh), plant out spring cabbages, calabrese, and purple sprouting broccoli.
• Herbs: Plant hardy herbs such as thyme, sage, and mint divisions into prepared borders.

Pest Monitoring

• Aphids & Slugs: Start checking for early infestations. Lay beer traps for slugs; encourage ladybirds for aphid control.
• Crop Rotation: Ensure brassicas are not planted where other brassicas grew last year to reduce clubroot risk.

Week 3 (May 15–21): Peak Sowing & Summer Cabbage Planting

Warm-Soil Sowing Outdoors

• Sweetcorn: Sow in blocks of at least four rows for adequate pollination. Plant every 30 cm.
• Courgettes & Pumpkins: If modules are well-rooted, transplant into final positions with 60–90 cm spacing.
• Cucumber: Sow outdoors in sheltered spots or under cloches; spacing about 30 cm between each plant.

Succession & Companion Planting

• Salad Crops: Sow rocket, mustard greens, and chicory for a staggered harvest.
• Intercropping: Plant radishes between slower-growing brassicas to maximize space.

Summer Cabbage & Leeks

• Summer Cabbage: Plant out plug plants 45 cm apart; use fine netting to protect from pigeons.
• Leeks: Plant out previously sown leeks in drills at a 3 cm spacing; blanch by earthing up soil.

Soil Moisture & Mulching

• Mulch: Apply well-rotted compost or leaf mould around seedlings to conserve moisture and suppress weeds.
• Watering: As temperatures rise, water early morning or late evening to reduce evaporation stress.

Week 4 (May 22–31): Late-May Planting & Maintenance

Final Direct Sowings

• French Beans: Last outdoor sowing for a late summer/autumn crop.
• Radicchio & Endive: Sow for autumn harvest; these tolerate slight frost.
• Turnips & Swedes: Sow thinly for root vegetables that store well.

Transplanting Under Cover

• Tomatoes & Peppers: Move hardened-off plants into greenhouse or polytunnel; plant deep to encourage strong root systems.
• Chillies & Aubergines: If large enough, transplant into pots or beds under protection.

Continuous Care

• Staking & Support: Tie in tomatoes, sweetpeas, and climbing beans to upright supports.
• Weeding & Hoeing: Keep on top of weeds to reduce competition for nutrients.
• Pest & Disease Check: Inspect leaves for mildew, caterpillar holes, and flea beetle damage; treat organically where possible.

Conclusion

May is a pivotal month on the allotment, bridging spring sowings and the onset of high summer growth. By following this week-by-week guide, you’ll harness the warming weather, optimize your sowing schedule, and protect young crops from late frosts and pests. Remember to keep records of what you sow and when, as this data is invaluable for refining your calendar next year. With careful planning, regular maintenance, and enthusiasm, your May efforts will yield a continuous, diverse harvest to enjoy through the warmer months and beyond.

Top 10 Questions & Answers

1. When is the last frost date for sowing tender crops on an allotment?
Typically between early to mid-May in southern UK, but always check local forecasts and soil temperature (aim for 10 °C+ for hardy crops, 15 °C+ for tender ones).

2. Can I sow courgettes directly outside in early May?
It depends on your microclimate. In most regions, sow in modules under cloches and transplant outdoors in mid-May when nights stay above 10 °C.

3. How often should I sow salad leaves in May?
Every 2–3 weeks to ensure a continuous supply and to account for bolting in hotter spells.

4. What’s the best way to protect brassica seedlings from pests?
Use fine mesh netting or horticultural fleece to exclude cabbage white butterflies and pigeons.

5. Which beans should I sow first—dwarf or climbing?
Dwarf beans can go in mid-May; climbing beans benefit from later sowings (late May) when soil is warmer for vigorous growth.

6. How deep should I plant onion sets and leeks?
Onion sets: cover to the base of the shoots (~2 cm deep). Leeks: plant so only the top 1–2 cm of the stem shows.

7. Is mulch necessary in May?
Yes—mulch conserves moisture, suppresses weeds, and adds organic matter. Use well-rotted compost or leaf mould.

8. What companion plants work well in May sowings?
Lettuce and radishes mutually benefit: radishes harvest quickly, leaving room for lettuce to take over.

9. How do I know if my tomatoes are ready to transplant outdoors?
They should be 15–20 cm tall with sturdy stems, hardened off over at least a week, and night temperatures consistently above 10 °C.

10. How to water newly sown seeds without washing them away?
Use a fine-rose watering can or mister, watering early/late and only when the topsoil starts to dry out.