The six-phase year
| Phase | Months | Dominant activity |
|---|---|---|
| Wake-up | Feb-Mar | Sowing seed indoors / heated propagator |
| Planting out | Apr-May | Pot on, harden off, plant out |
| Growing | Jun-Jul | Daily care, vertical training, first harvests |
| Peak | Aug-Sep | Harvest, daily watering, succession |
| Wind-down | Oct-Nov | Final harvests, winter crops in, clean-up |
| Rest | Dec-Jan | Maintenance, plan, propagator only |
Each month below = what's priority (do first) vs what's optional (nice to have).
January — propagator, planning, maintenance
Priority:
- Annual greenhouse deep clean — pick a dry day, empty the structure, wash polycarbonate panels (warm water + mild soap, NOT bleach which yellows the UV layer), sweep, wipe staging
- Order seeds for the year — tomato, cucumber, pepper, salads. Deliveries can run late if you wait until February rush
- Check structure — base anchoring tight, frame fixings tight, vent piston functional
Nice to have:
- Sow onion seed for early crop (mid-late January in heated propagator)
- Start chitting seed potatoes (set in egg trays, eyes up, cool light spot)
- Sow first batch winter salads if heat available
Critical not-to-do: sow tomato/cucumber/aubergine seed yet — UK January light insufficient, seedlings stretch. Wait for February-March.
→ Deeper read: Wooden Greenhouse Maintenance UK — the real schedule
February — sowing season begins
Priority:
- Late February: sow tomato seed in heated propagator (18-22°C). Cordon varieties for best UK greenhouse yield
- Sow aubergine + pepper seed — they need a longer start than tomatoes (12-14 weeks indoors)
- Sow celery, celeriac, salads for spring harvests
- Check overwintered crops — brassicas, hardy salads, garlic
Nice to have:
- Sow sweet peas for early summer flowers
- Force rhubarb under a cover for tender pink stalks
- Start propagating cuttings of dahlias if you overwintered tubers
Maintenance:
- Check vents open + close fully on the first sunny days
- Watch for greenfly arriving on overwintered crops
March — propagation peak
Priority:
- Sow cucumber, courgette, melon, squash mid-late March in propagator
- Pot on tomato seedlings to 9-cm pots when first true leaves appear
- Sow main batches of salads, lettuce, rocket directly in greenhouse soil
- Sow basil, coriander, dill for kitchen herbs
Plant out (in greenhouse, NOT outdoors):
- Hardy lettuces, rocket, mustard, chard
Maintenance:
- Start ventilation routine — open vents at 15°C+ daytime, close at evening
- Top-dress soil-grown beds with compost / slow-release fertiliser
Nice to have:
- Sow flowers for greenhouse pots (calendula, nasturtium, marigold — companion plants)
April — pot on, harden off
Priority:
- Pot tomato seedlings on to 13-15 cm pots mid-April
- Pot cucumber seedlings on — same timing
- Harden off outdoor-bound seedlings (bring greenhouse-grown plants outside daytime, back at night) — over 7-10 days before planting outdoors
- Sow successional salads weekly — leaf lettuce every 2 weeks for continuous harvest
- First sow of French beans in pots (if greenhouse heated) for early crop
Maintenance:
- Watch for whitefly on cucumbers (introduce yellow sticky traps as monitoring)
- Begin overhead damping down on warm days for cucumber humidity
- Ensure heater off, vents working well
Plant out outside (greenhouse-raised):
- Hardy annuals, sweet peas, early peas, broad beans (if hardened off)
May — the planting-out month
Priority:
- Early-mid May: plant out tomatoes into final greenhouse position. Greenhouse min night temp must be 10°C+. Install supports (string-to-ridge or canes) at same time
- Plant out cucumbers into pots/grow-bags, train up canes
- Plant out peppers, chillies, aubergines into pots
- Plant out basil in pots near tomatoes (companion + culinary)
Outside (greenhouse-raised seedlings):
- Plant out runner beans, French beans (after frost risk passed)
- Plant out courgettes, squash, pumpkin (after late frost risk)
Maintenance:
- Increase watering as plants grow + temperatures rise
- Side-shoot cordon tomatoes weekly starting now
- Continue ventilation discipline — open vents fully on warm days
→ Deeper read: How to Grow Tomatoes in a Greenhouse UK — full tomato calendar in detail
June — first flowers, first feed
Priority:
- Side-shoot cordon tomatoes weekly — pinch out every shoot in the leaf axil
- Train cucumbers up supports, remove tendrils
- Start liquid tomato feed when first truss has set fruit (typically mid-late June)
- Pollinate — tomatoes are self-pollinating but a gentle shake of the plant in the morning helps fruit set; cucumbers may need hand-pollination if no insects entering
Maintenance:
- Daily watering becomes essential by late June
- Damping down on hot days (water the path, not the plants) raises humidity for cucumbers
- Watch for blossom-end rot (BER) on tomatoes — sign of inconsistent moisture
Nice to have:
- Sow autumn salads (mizuna, mustard, rocket) for September-November crops
- Sow late beans (French climbing) for September crop
July — first harvests, daily care
Priority:
- First ripe tomatoes (cordon, mid-late July depending on variety)
- Daily watering for established greenhouse crops
- Weekly tomato feed continues; switch to twice-weekly by end of month
- Continue side-shooting cordons; remove lower leaves below ripening trusses for airflow + light
- Harvest cucumbers every 2-3 days at this size — letting them go full-size slows next fruit production
Maintenance:
- Vents open from sunrise — internal temperatures exceed 35°C+ by 10am on summer days (SmartVent™ wax-piston auto-vents handle this without your intervention)
- Damping down twice daily on 30°C+ days
- Watch for red spider mite — small webs on undersides of leaves (cucumbers especially). Biological control: Phytoseiulus persimilis predatory mite (standard horticultural approach)
Nice to have:
- Sow late beetroot, chard, autumn brassicas
- Sow late carrots in deep containers
August — peak production
Priority:
- Peak harvest — tomatoes, cucumbers, peppers, basil daily
- Daily watering, sometimes twice on 30°C+ days. Plan: 2-3 L per cordon plant
- Twice-weekly tomato feed through August
- Stop pinching new flowers on cordons (after 6-8 trusses) — too late in season to ripen new fruit
- Tomato truss support — long heavy trusses can break stems; tie up with soft tie
Maintenance:
- Holiday absence planning — daily watering is non-negotiable in August. Auto-watering kit (~£40 + setup) OR neighbour visits
- Watch for late blight (Phytophthora) — humid evenings increase risk; keep vents open
Plant out (autumn crops):
- Plant out autumn brassica seedlings (Brussels sprouts, kale, kohlrabi) outdoors
- Sow spring cabbage outdoors
September — autumn shift
Priority:
- Continue harvest — tomatoes still ripening, cucumbers slowing, peppers maturing
- Reduce watering frequency as nights cool (every 2 days from mid-Sept)
- Stop feeding mid-September — let final trusses ripen on stored sugars
- Pinch out top growing tip of cordon tomatoes early September — diverts energy to ripening, not new growth
Sow / plant for autumn-winter crops:
- Hardy salad mixes (winter lettuce, mizuna, mustard, rocket)
- Winter spinach + chard
- Garlic (plant cloves directly in soil for next-year harvest)
- Overwintering broad beans (Aquadulce variety reliable)
Maintenance:
- First condensation on cool mornings — wipe down, prevent fungal disease build-up
- Begin closing vents earlier in evening as temperatures drop
October — wind-down and clean-out
Priority:
- Final tomato harvest mid-late October — green tomatoes ripen indoors in paper bag with a banana
- Pull spent plants — tomatoes, cucumbers compost (cucumber stems can rot heap, chop fine)
- Deep clean — wash polycarbonate inside + out, sweep, replace top-dress soil if direct-grown
- Plant garlic, broad beans if not done in September
- Sow winter salads in propagator for hardening off into greenhouse
Maintenance:
- Vent piston service — wipe rod, check hinge bolts
- Apply yearly wood preservative top-up if it's been 2+ years since last full re-treatment
→ Deeper read: Wooden Greenhouse Maintenance UK
November — winter prep
Priority:
- Insulate if growing through winter — bubble-wrap roll on the inside of glazing keeps temperature 2-4°C higher (cheap winter coat, takes a Saturday)
- Set up frost protection for tender perennials (lemon trees, fig in pot, chilli plants you're overwintering)
- Check ground anchoring before storm season — corner brackets, ground screws if installed
Plant / harvest:
- Continue harvesting hardy winter salads
- Force chicory for white shoots
- Plant lily bulbs in deep pots for early-summer flowering
Storm season prep: check that EasyMount™ galvanised steel corner-brackets are tight at the base; verify ground-screw anchoring if installed; tighten any frame fixings backed out from a season of timber movement.
→ Deeper read: How to Insulate a Greenhouse for UK Winters
December — rest period
Priority:
- Annual winter task — empty propagator, clean staging, take stock of remaining seed inventory
- Order seed for next year before late-January rush
- Plan next year's growing layout — what worked, what didn't, what to try
Plant / harvest:
- Continue winter salads (mizuna, mustard cress, rocket — hardy types)
- Force rhubarb / chicory under cover
Maintenance:
- Inspect frame for surface checks, soft spots — annual visual check
- Confirm vents close fully, fixings tight before Storm Arwen-grade winds
→ Deeper read: Wooden Greenhouse Maintenance UK — the real schedule for the full task list
What this calendar assumes
This calendar assumes:
- UK domestic greenhouse (not commercial)
- Unheated OR mildly heated (frost protection only)
- Standard NORDIC-equivalent dimensions (5.2-15.6 m² floor, 2.30 m ridge)
- Average UK weather (varies regionally — Scotland 2 weeks later, southwest 2 weeks earlier)
Heated greenhouses can sow 2-4 weeks earlier and crop year-round. The economics rarely justify heating unless you're growing for sale.
Northern UK growers add ~10 days to all "first action" dates. Southwest growers can subtract 5-7 days.
Frequently asked questions
When should I start using my greenhouse for the year?
January is maintenance + planning. Late February kicks off real activity with the first tomato/aubergine/pepper sowings in a heated propagator. Don't wait until April — too late for the long-cropping summer veg.
What can I sow in a greenhouse in March?
Tomato (if not already done in February), cucumber, courgette, melon, basil, salads, herbs. Pot on February-sown tomato seedlings to 9-cm pots in March. Continue propagator at 18-22°C for warm-season crops.
When can I plant out tomatoes in my UK greenhouse?
Early-mid May, when greenhouse minimum night temperature is reliably 10°C+. Earlier planting (April) sees seedlings sulk in cold soil and produces a poorer crop than waiting 2 weeks for the warmth.
What grows in a greenhouse in winter?
Hardy salads (mizuna, mustard, winter lettuce, rocket), chard, spinach, garlic (planted October-November for next year's harvest), broad beans (overwintering varieties), forced chicory, frost-tender perennials kept alive (lemon, fig in pot, overwintering chilli plants).
Do I need to heat my greenhouse?
For UK greenhouse growing, no — unheated is fine for March-October growing. Winter heating is only worth it if (a) you're growing through frost period (tomatoes won't, but tender perennials might), (b) you commercially grow, or (c) you want year-round salad harvest. Most domestic growers find frost protection (electric oil radiator on thermostat at 3°C) is enough.
→ Deeper read: Greenhouse Heating UK Winter for the cost analysis
When is peak harvest season for UK greenhouse?
August-September. Tomatoes peak ripening, cucumbers still cropping, peppers maturing, basil thriving. Daily harvest visits + daily watering = 30 mins/day commitment for ~6 weeks. Planning holidays around this is real — auto-watering kit (£40) or family minder for August is essential.
What's the difference between greenhouse and outdoor growing seasons?
A greenhouse extends both ends — start 6-8 weeks earlier in spring (heated propagator), continue 4-6 weeks later in autumn (frost protection). Total useful growing window: 9-10 months greenhouse vs 5-6 months outdoors. Specific heat-loving crops (tomatoes, cucumbers, peppers, aubergines, basil) are 2-3× more productive under glass/PC.
Can I grow vegetables in a greenhouse year-round?
Hardy salads + leafy greens yes (mizuna, lettuce, rocket, chard, spinach, kale, mustard). Tomatoes/cucumbers/peppers no — they need warmth + light that UK November-February doesn't provide regardless of greenhouse. Garlic + overwintering broad beans yes (planted October, harvested July).
Final CTA
A wooden greenhouse with 2.30 m ridge + screw-fixed polycarbonate handles this calendar reliably year-round — the structural durability matters when you're carrying 10+ months of growing through November storms and February frosts.
→ Browse the NORDIC range — five sizes from £1,499 → How to Grow Tomatoes in a Greenhouse UK — full tomato detail → Wooden Greenhouse Maintenance UK — what to do annually to the structure itself