The Complete Irish Greenhouse Planting Guide (By Month)

An Irish greenhouse planting guide for a polycarbonate greenhouse is one of the best upgrades for Irish gardens. Because it helps buffer plants from wind, heavy rain, and cold nights, while the panels diffuse light and improve insulation compared to exposed growing.

This Complete Irish Greenhouse Planting Guide (By Month) shows exactly what to sow, plant, and harvest each month in Ireland, so you can keep your greenhouse productive in every season—whether you have a 2×4, 3×6, 3×8, 3×10, or 3×12 polycarbonate greenhouse.

January: Start Slow, Grow Steady

What to sow in a greenhouse (Ireland):

• Winter lettuce (cold-tolerant)
• Spinach
• Parsley (slow germination)

What to grow/harvest:

• Overwintered salad leaves
• Hardy herbs in pots

Irish greenhouse planting guide tip: Vent briefly on dry days to reduce condensation and mould.

February: Early Seed Starting Begins

Sow / start:

• Onions from seed
• Lettuce, spinach, rocket
• Tomatoes (only if you can provide warmth/light)

Grow/harvest:

• Salads and hardy greens

Irish greenhouse planting guide Tip: Use modules and avoid overwatering—damp + low light encourages fungal issues.

March: Main Sowing Month for Many Growers

Sow / start:

• Tomatoes (common main sowing time)
• Spring onions
• Herbs: coriander, dill, chives
• Beetroot in modules (for tidy transplanting)
• Lettuce (succession starts)

Plant / move:

• Harden off sturdy seedlings in daytime mild spells

Tip: Start regular ventilation—March sun can heat a greenhouse quickly even in Ireland.

April: Pot Up and Prepare for Summer Crops

Sow / start:

• Cucumbers (better once greenhouse is milder)
• Courgettes (late April to avoid leggy plants)
• Basil (needs warmth)
• More lettuce every 2–3 weeks

Plant / pot up:

• Tomatoes into larger pots / final positions (depending on warmth)

Tip: Add staging/shelves—especially helpful in smaller polycarbonate greenhouse sizes.

May: The Greenhouse Fills Up

Plant:

• Tomatoes into final beds/grow bags
• Cucumbers into final spots
• Peppers (only once nights are reliably mild)

Sow (succession):

• Lettuce, rocket, spring onions
• Herbs for constant picking

Tip: Water early in the day and keep airflow moving—this is a key month for disease prevention.

June: Train, Tie, and Keep Things Moving

Do now:

• Train tomatoes up strings/canes
• Tie in cucumbers and keep them supported
• Keep spacing open for airflow

Sow:

• More salads and herbs
• (Larger greenhouses) dwarf French beans can work well

Harvest:

• Herbs, salads; early cucumbers in many setups

July: Peak Growth and Heat Management

Harvest:

• Cucumbers (often daily)
• Tomatoes (many varieties start producing now)
• Basil and other herbs

Sow:

• More lettuce (bolt-resistant types)
• Spinach (for late summer)

Tip: Use shade cloth during hot spells—polycarbonate diffuses light but temperatures can still spike.

August: Switch Toward Autumn Crops

Sow / start:

• Winter lettuce
• Spinach
• Pak choi / Asian greens (often better as it cools)

Harvest:

• Tomatoes, cucumbers, herbs

Tip: Remove older leaves near the base of plants to improve airflow and reduce humidity pockets.

September: Extend the Season in Ireland

Sow / plant:

• Winter salads (mizuna, mustard greens, lamb’s lettuce)
• Spinach
• Spring onions (overwintering types)

Harvest:

• Late tomatoes and cucumbers (as long as temps allow)

Tip: Reduce watering slightly—lower light means slower drying and more condensation risk.

October: Winter Greenhouse Growing Starts Properly

Plant / grow:

• Winter lettuce
• Spinach
• Hardy herbs (parsley, chives)

Greenhouse hygiene:

• Clear spent summer vines
• Clean benches and pots to reduce pests/disease carryover

November: Low Light, Smart Choices

Grow/harvest:

• Winter salad leaves
• Spinach
• Herbs (slow, but steady)

Avoid: Starting tomatoes/cucumbers now unless your greenhouse is heated and you have extra light.

December: Protect and Prepare

Harvest:

• Winter salads and spinach
• Hardy herbs

Tip: Keep watering light but consistent. Consider insulating the base and using bubble insulation inside to reduce heat loss.

Best Crops for Polycarbonate Greenhouses in Ireland (Reliable Winners)

However, if you want “low-regret” choices for Irish weather, these usually perform very well:

• Tomatoes
• Cucumbers
• Salad leaves (succession sowing)
• Spinach (spring + autumn/winter)
• Herbs (basil in summer; parsley/chives nearly year-round)
• Peppers (best in warmer, sheltered setups)

FAQ

What can I grow in an unheated greenhouse in Ireland in winter?

Winter salads, spinach, and hardy herbs are the most reliable. Growth is slower, but you can still harvest regularly.

When should I start tomatoes in a greenhouse in Ireland?

Typically March is a safe main sowing month for unheated greenhouses, while late February can work if you provide warmth and good light.

In conclusion, with the right timing, you can grow something in your greenhouse every month—even in Ireland. Use this planting calendar to plan successions, keep the greenhouse productive, and extend your season well beyond outdoor growing.

Therefore, if you’re choosing or upgrading, polycarbonate greenhouses are a strong fit for Irish conditions thanks to their insulation and light-diffusing panels—available in sizes 2×4, 3×6, 3×8, 3×10, and 3×12 to suit every garden.

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