How to Prepare Your Greenhouse for Spring
Spring greenhouse preparation covers deep cleaning, glass scrubbing, soil replacement, ventilation setup, and pest prevention. With 16 years of greenhouse installations behind us, we have seen how a proper February clean transforms results. Algae buildup alone can reduce light transmission by up to 40%, starving early seedlings of the energy they need. A single weekend of focused preparation sets your greenhouse up for the entire season ahead.
Key Takeaways
- Deep clean in late winter – remove debris, wash surfaces, eradicate overwintering pests before they breed
- Scrub all glazing panels – dirty glass cuts light by up to 40%, stunting early seedlings
- Replace spent compost – fresh growing medium prevents disease carryover from last season
- Check structure and seals – fix cracked panes, loose clips, and draughty door seals before planting
- Set up ventilation early – automatic vent openers protect plants from overheating on warm spring days
Installer's Note
Every February I walk into greenhouses that have sat untouched since autumn. Cracked panes, algae-coated glass, dead plants rotting in corners. It is always the same story. Late February to early March is the ideal window for a deep clean. The greenhouse is mostly empty and the days are getting longer. Get it done now and you are ready to sow the moment spring arrives.
Why Clean Your Greenhouse?
Cleaning your greenhouse is not optional. It is one of the most important tasks in the growing calendar. A winter greenhouse is a haven for pests that would normally die in the cold. Slugs, aphids, red spider mite and mealy bugs all hibernate in hidden corners.
We have seen greenhouses where overwintering pests destroyed entire trays of seedlings within days. A thorough deep clean removes these threats before they wake up. It also eliminates the germ buildup that causes fungal disease in young plants. If you want a head start on greenhouse pest control, the spring clean is your first line of defence.
Even your greenhouse staging needs a proper scrub. Pests love to hide underneath shelves and in the gaps between slats.
When to Clean
Wait for a dry, mild day in late February or early March. If your greenhouse is mostly empty, you can start straight away. If you overwinter tender plants, move them to a sheltered spot first. Wrap them in fleece or place them in a conservatory while you work.
You can work around plants, but the result will not be as thorough. Switch off any electricity before splashing water around. Dry the glass gently afterwards to avoid streaking.
Clear Out Everything
Start by removing absolutely everything from your greenhouse. Old plants go on the compost heap. Pots, tools, and trays all need washing. If you find any diseased plant material, burn it rather than composting it. Disease spores survive composting and spread to new seedlings.
Sweep the floor and clear debris from every corner. Check behind staging and under shelving. Keep a close eye out for slugs, snails, and their eggs.
Disinfect Everything
Fill a bucket with hot, soapy water and wash down all shelves, pots, and planters. An eco-friendly garden disinfectant works well for stubborn grime. Make sure you rinse everything thoroughly before reusing it.
We find it helpful to have a large container for soaking smaller items. A hosepipe speeds up the rinsing process. Pay extra attention to the undersides of shelves and the inside of pots where mould hides.
Clean the Glazing
This is the single most impactful job in your spring clean. Algae and mildew thrive on greenhouse glass in warm, moist conditions. We have measured light reductions of up to 40% on badly neglected panes. That lost light stunts early seedlings when they need it most.
Use hot, soapy water and a stiff bristle brush to scrub each pane. A pipe cleaner reaches the cracks between overlapping glass panels. For a detailed walkthrough, read our guide to cleaning greenhouse glass.
Once the glass is clean, keep a soft brush handy throughout the season. A quick sweep every few weeks removes dirt, leaves, and cobwebs before they build up again.
Replace Potting Soil
Compost in growing beds should be partially replaced each spring. Old soil harbours disease spores and depleted nutrients. Your new plants need a clean, nutrient-rich growing medium to establish strong roots.
Remove the top 5–10 cm of old compost and replace it with fresh multipurpose or peat-free mix. If you grow directly in greenhouse borders, add well-rotted manure or garden compost to restore fertility.
Set Up Ventilation
Good airflow is your best defence against fungal disease. Plants thrive when air moves freely through the greenhouse. We recommend four vents for proper circulation. Fit two slatted louvre vents low on opposite sides and two roof vents at the top.
Louvre Window Vents
Greenhouse louvre window vents sit low on the greenhouse frame. While roof vents let warm air escape, louvres draw cool air in from below. This creates a natural convection cycle that regulates humidity and keeps plants comfortable.
Automatic Vent Openers
Automatic vent openers are one of the best investments for any greenhouse. They open roof vents when temperatures rise and close them when it cools down. No electricity needed. We fit these on most installations because spring weather is unpredictable. One warm afternoon with closed vents can kill a tray of seedlings.
Plan Your Spring Planting
With a clean greenhouse and fresh compost, you are ready to start sowing. In late February and March, hardy crops like lettuce, broad beans, and peas can go in. By April, tomatoes, peppers, and cucumbers are safe to start under glass.
Plan your layout before you sow. Tall crops like tomatoes need the back or north side. Low growers sit at the front where they will not be shaded. For a full month-by-month schedule, see our guide to growing seeds in a greenhouse.
Matt's Tip: The February Window
I always aim to get the spring clean done in the last week of February. The greenhouse is at its emptiest and the days are just starting to lengthen. Last year I found a nest of slug eggs behind the staging. They would have hatched into hundreds of hungry slugs by March. Catching problems like that early saves your entire spring sowing. Do not put it off until March when you will be too busy seed starting.
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Matt's Pick for Spring PreparationBayliss MK7 Automatic Roof Vent Opener Best For: Hands-free temperature control during unpredictable spring weather Why I Recommend It: Spring temperatures swing wildly. One warm afternoon can cook seedlings if vents stay shut. The Bayliss MK7 opens your roof vent automatically when temperatures rise. No electricity needed. We fit these on most installations and they last for years. £89 View This Autovent → |
Frequently Asked Questions
When should I start preparing my greenhouse for spring?
Late February to early March is the ideal time. The greenhouse is usually at its emptiest after winter. Days are lengthening, giving you better working light. Starting early means your greenhouse is clean and ready before the main sowing season begins in March and April.
How do I clean greenhouse glass without streaks?
Use hot soapy water and dry with a soft cloth. Scrub each pane with a bristle brush to remove algae and mildew first. Then rinse with clean water. Dry gently using a microfibre cloth or chamois leather. Work on an overcast day so the glass does not dry too fast and leave water marks.
Should I replace all the compost in my greenhouse each year?
You do not need to replace all of it. Removing the top 5–10 cm and adding fresh compost is usually enough. This removes the layer most likely to harbour disease spores and depleted nutrients. If you had serious disease problems last season, a full replacement is worth the effort.
Do I need automatic vent openers in a greenhouse?
They are one of the best greenhouse investments. Spring temperatures are unpredictable. A single warm afternoon with closed vents can overheat and kill young plants. Automatic openers react to temperature changes without electricity. They open when it warms up and close when it cools down.
How do I stop pests returning after a spring clean?
Thorough disinfection is the most effective prevention. Wash all surfaces, staging, and pots with garden disinfectant. Check under shelving and behind staging for slug eggs. Remove all old plant debris rather than leaving it to compost in situ. Inspect new plants before bringing them into the greenhouse, as they often carry hitchhiking pests.
Related Articles
- Cleaning Your Greenhouse
- The Best Way to Insulate a Greenhouse
- Best Position for a Greenhouse UK
- Seed Sowing Month by Month UK Guide
- The Best Beginners Greenhouse
Questions about greenhouse spring preparation? Email us at info@greenhousestores.co.uk
