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Greenhouses & greenhouse gardening

Help solve your gardening problem. Here are the answers to some commonly asked gardening questions about greenhouses and greenhouse gardening with hints, tips and advice.

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I have bought a small electric heater and have lined the roof and walls with bubblewrap. I now find that I have condensation between the bubblewrap and the glass. 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?

Amateur greenhouse fumigants have been removed from the market, apart from sulphur candles. 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 sprays and yellow sticky traps, but I still cannot get rid of whitefly. How do I eradicate this pest?

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.

All of my geraniums succumbed to a disease. 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 plants become debilitated and virtually stop growing. What is it and how can I prevent it or control it if it reappears next year?

Your geraniums (pelargoniums) are suffering from the disease pelargonium rust. Rusts are difficult to control and in severe case it's often best to throw out your stock as it will spread to other geraniums.

New plants can be protected by spraying with an approved fungicide. 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.


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