Fristly, remove everything being stored or grown under glass, including portable shelving units. Then, take a sponge with warm, soapy water to thoroughly wash all panes of glass, both inside and outside. Then rinse off with clean water. Use a long-handled sponge to clean the panes of glass out of arm’s length reach, rather than a ladder for safety reasons.
It’s important to remember to clean the glazing, both inside and out. Also, if you’re doing this as a job throughout the year, this is also the opportunity to wash off any shade paint that was put onto the windows to control sunlight.
Doing a thorough clean will give the chance to check for any breakages or damage from winter weather. Then you can make or plan any repairs to ensure the greenhouse is in the best condition for the rest of the year.
Next, check ventilator glass and remove accumulated debris using the thin edge of a garden label to scrape the debris away.
Also, thoroughly wash stored seed trays and pots to rid them of any accumulated slug and snail eggs.