If there's anything you want to know about gardening - get in touch

Professional services
My professional horticultural services

Need a speaker?
For horticultural societies & clubs

Garden Answers FAQ
Answers to commonly asked questions

Question time
How do I look after container plants?
How do I look after my lawn in spring?
How do I prune clematis?
Why aren't my daffodils flowering?
How do I cope with flooding?

Pest Watch
Lily beetle control
Vine weevil control
Whitefly control
Clematis wilt

Links
Links to useful websites

My blog
View my blog

Gardening products & plants
You can buy a wide range of plants, seeds & products from the follwing recognised companies in confidence.

Find out more about shopping

Garden answers

Greenhouses

Help solve your gardening problem. Here are the answers to some commonly asked gardening questions about greenhouses and greenhouse gardening.

If you are unable to find the answer here, then send me an e-mail

I have a small greenhouse. Recently, in an attempt to protect some overwintering plants and to be able to start some seed sowing, I have bought a small electric heater and I have also lined the roof and walls with bubblewrap. I now find that I have condensation between the bubblewrap and the glass, particularly on the roof. What am I doing wrong (presuming of course that this is an unwanted development!)?

This is quite common - it may just mean that you are overwatering your plants or that moisture from the ground is evaporating.

I would try and increase ventilation on warm days in winter - just make sure vents and doors are shut by no later than 4pm.

The condensation will cut down on light reaching the greenhouse - but providing you're not keeping the temperature too high which may encourage spindly growth - there's nothing much really to worry about. Obviously, seedlings will become very drawn in these conditions. I do know gardeners who grow for exhibition who will remove the condensation daily with a cloth - but I'm sure in your case opening the vents on warm days will be adequate.

I have been trying to source fumigation 'bombs' to kill the pests and diseases overwintering in my greenhouse, but have been advised these are no longer sold. How do I eradicate pests for the winter and prevent them from re-occurring next spring?

Amateur greenhouse fumigants have been removed from the market, apart from sulphur candles which are for diseases. Professionals can still get their hands on approved products.

You can still sterilise the greenhouse and staging with Jeyes Fluid or Armillatox, which will help kill overwintering eggs and disease spores.

I have used most of the sprays and yellow sticky traps, but I still cannot get free of whitefly. I grow geraniums, carnations and tomatoes mainly in the greenhouse. Do you have the answer to eradicate these pests please?

There is a page on the site dedicated to the control of whitefly.

Basically, whitefly are very fast breeders and any chemicals have to be applied regularly to break the lifecycle.

I have now cured whitefly in my greenhouse using the biological control encarsia.

Every one of the geraniums in my greenhouse succumbed this year to a disease that occurred only mildly last year. It takes the form of rusty brown-red spots on the undersides of the leaves - on the surface of the leaves it shows as lighter patches of green. The plant becomes debilitated and virtually stops growing. It spread throughout the whole of my greenhouse - affecting all my geraniums very badly, except trailing geraniums, which were hardly affected. It also affected geraniums bedded outside.

What is it and how can I (a) prevent it or (b) control it if it reappears next year? I have since destroyed by entire stock of geraniums, except for the trailers.

Your geraniums (pelargoniums) are suffering from the disease pelargonium rust. Rusts are difficult to control and in your case you've done the right thing in throwing out your stock.

New plants can be protected by spraying with a good fungicide such as Dithane. And I stress protect - that is you spray the plants to protect them from getting the disease. If you try and control a severe outbreak you won't have much success.

Back to GardenForum Horticulture homepage

GardenForum: Somewhere to discuss horticulture & gardening