Many thanks for your recent enquiry regarding the winter cleaning of your greenhouse. I’ve always washed down our Kitchen Garden greenhouse with Jeyes Fluid and then pressure-washed both the interior and exterior. This extensive cleaning regime has certainly removed any over wintering pests from the framework of the structure, but don’t have any illusions – you have to clean every tiny crevice and gap! Of course, you don’t have to use Jeyes Fluid – I’m sure that other cleaners, such as Algon and Citrox will do just as good a job. I find the pressure washing is ideal for removing any traces of algae or general dirt and grime, which, as I’m sure you know, will affect the quantity and quality of light entering the greenhouse. It also has the added advantage of blasting any pests which have crept into the tiniest of holes to hibernate, such as red spider mite – which, incidentally, are only coloured orangey/red during the winter!
With regard to growing in greenhouse border soil, there are various techniques you can use to ensure pests – and most importantly, diseases – do not remain in the soil over winter. Sterilising the soil through heat treatment is one option (there are electrical sterilisers readily available); planning and adhering to a crop rotation cycle will also help, but probably the most sure-fire method is to remove and replace large quantities of the soil, a practice we follow in the Kitchen Garden greenhouse. The latter is also a great excuse for topping up your borders with organic matter as well!
I hope you enjoy a successful second season of growing!