In The Greenhouse This June

June is when the greenhouse shifts from “growing on” into full summer production mode. Temperatures can swing dramatically, so the main priorities are ventilation, watering, feeding, and keeping plants under control before they turn into a jungle.

🌡️Ventilate aggressively on warm days

The biggest June greenhouse mistake is overheating.

On sunny days:

• Open doors and roof vents early
• Create airflow through the greenhouse
• Use automatic vent openers if possible

Greenhouse temperatures can exceed 35°C very quickly in June.

Poor airflow encourages:

• Mildew
• Grey mould
• Whitefly
• Weak growth

🌤️Shade during heatwaves

Strong midday sun can scorch plants and stress seedlings.

Useful options:

• Shade paint
• Shade netting
• Temporary fleece or mesh

Especially important for:

• Young plants
• Cucumbers
• Lettuce
• Newly transplanted crops

💧Water consistently — but intelligently

Plants are growing fast now.

Best practice:

• Water thoroughly
• Water roots, not foliage
• Early morning is ideal

Avoid:

• Little splashes every few hours
• Constantly soggy compost

Containers and growbags may need daily watering in warm weather.

🥒Feed fruiting crops weekly

Once tomatoes, cucumbers, peppers, and aubergines start flowering:

• Begin regular feeding
• High-potash tomato feeds work well

Hungry greenhouse crops quickly exhaust compost nutrients.

🍅Pinch out tomato side shoots

For cordon tomatoes:

• Remove side shoots weekly
• Tie stems securely as they grow

This:

• Improves airflow
• Focuses energy into fruit
• Prevents overcrowding

Bush varieties usually don’t need pinching.

🪢Support plants before they collapse

June growth can suddenly become explosive.

Check regularly:

• Tomato strings/canes
• Cucumber supports
• Pepper stakes

It’s much easier to support plants early than rescue snapped stems later.

🥒Increase humidity for cucumbers

Cucumbers prefer more humidity than tomatoes.

Helpful tricks:

• Damp greenhouse paths
• Water trays
• Grouping plants

But maintain ventilation to avoid fungal disease.

🍅Pollinate greenhouse crops if needed

Tomatoes usually self-pollinate better with movement.

You can:

• Gently tap flower trusses
• Shake supports lightly midday

This improves fruit set during still weather.

🍂Remove yellowing lower leaves

Especially on tomatoes:

• Improves airflow
• Reduces disease risk
• Helps ripening later

Remove leaves gradually rather than stripping plants suddenly.

🪰Watch for pests every few days

Greenhouses can turn into pest factories in June.

Common problems:

• Whitefly
• Red spider mite
• Aphids
• Fungus gnats

Check:

• Undersides of leaves
• Growing tips
• Around vents and staging

Early detection makes control far easier.

🌱Avoid overcrowding

June plants often outgrow the greenhouse faster than expected.

Thin or move out:

• Spare seedlings
• Excess herbs
• Overcrowded trays

Good spacing dramatically reduces disease.

🌱Harden off plants carefully

If moving plants outdoors:

• Acclimatise gradually over 7–10 days
• Avoid sudden full sun or cold nights

Even June nights can still check tender plants.

🧹Keep greenhouse paths and surfaces clean

Warm damp conditions encourage disease.

Regularly:

• Remove dead leaves
• Clear fallen fruit
• Wash algae from paths and staging

Good hygiene matters much more in summer.

🪟Open up on humid evenings after hot days

After very warm days:

• Ventilate into the evening if temperatures stay mild

This reduces condensation overnight, which helps prevent fungal problems.