In The Greenhouse This May

May is when a greenhouse shifts from “nursery mode” into full production. Temperatures rise quickly, plants grow fast, and small mistakes (like overheating or missed watering) can escalate quickly. Here’s how to stay on top of it:

🌡️ Ventilation is everything

On sunny May days, a greenhouse can overheat fast—even if it’s cool outside. Open vents and doors daily, and consider automatic vent openers if you’re not always around. Good airflow also reduces disease.

🌱 Harden off plants gradually

Seedlings raised inside need time to adjust before going outdoors. Start by putting them outside during the day and bringing them in at night for about 7–10 days.

🍅 Plant up summer crops

This is prime time to move crops into their final positions:

• Tomatoes
• Cucumbers
• Peppers
• Aubergines

Use large pots or grow bags, and support plants early to avoid damage later.

🪴 Feed regularly

Fast-growing greenhouse crops are hungry. Once plants are established:

• Use a balanced feed initially
• Switch to a high-potash feed (like tomato fertiliser) once flowering starts

💧 Stay on top of watering

Plants can dry out quickly as temperatures rise. Check daily:

• Water in the morning or evening
• Avoid wetting leaves to reduce disease
• Consider capillary mats or drip systems if you’re busy

☀️ Provide shade when needed

Strong sun can scorch young plants. Use shading (netting, blinds, or even a light whitewash) during hot spells.

🐝 Help with pollination

In a closed greenhouse, pollinators are limited. For crops like tomatoes:

• Gently tap or shake flowering trusses
• Or use a small brush to transfer pollen

🐛 Watch for pests early

Warm conditions are perfect for:

• Aphids
• Whiteflies
• Red spider mites

Check undersides of leaves regularly and act early before infestations spread.

🧼 Keep it clean and tidy

Remove dead leaves, spilled compost, and old plant material. Good hygiene reduces pests and fungal problems.

🪟 Maximise space

Use vertical growing:

• Hang baskets
• Add shelves
• Train plants upwards

This helps you grow more without overcrowding.

🌙 Be ready for temperature swings

Days can be hot, nights can still be chilly. Keep fleece or bubble wrap handy to protect plants if temperatures dip.