Experienced gardeners will tell you that you can never be quite sure what will happen in a season, and pests, diseases and other plant conditions can cause an unwanted blight in your impressive display, and often without warning.

Sometimes these situations are simply unavoidable, but knowing what to do when they do arise ensures that appearance, balance and harmony can be restored as quickly as possible!

Oedema is one such plant condition, and it seems to be particularly prevalent in gardens across the area right now – so here is our guide to the issue.

Cause & Symptoms

Oedema is caused when we have low night time temperatures, high day time temperatures – and something we’re all familiar with – too much rain!

In these conditions, plants take up more water than they can lose through their leaves by transpiration.  As a result, water-soaked spots appear on the leaves which become raised warty or pimple-like swellings or growths.  These growths can rupture and have a white, powdery appearance or they may appear as rust-coloured scaly patches – and on woody plants, it’s not uncommon for corky spots or ridges to develop.

Treatment & Prevention

The first rule for treatment is not to be tempted to remove the affected leaves! They may not look good, but the condition isn’t infectious and removing affected leaves has the effect of reducing the leaf area available for transpiration, which in turn makes the problem worse.

Instead you should concentrate on improving conditions in the air and soil to encourage healthy new growth in the following ways:

• Improve your soil texture by incorporating organic matter such as well-rotted manure or leaf mould, this should help avoid waterlogging in heavy rain.
• Don’t plant in very wet conditions, particularly if you are gardening on clay soil.
• If your affected plants are in containers, check the compost is free-draining and if the plants are too wet, re-pot them using fresh compost.  If your affected plants are grouped in containers then increase the air circulation around them by spacing them further apart.
• Plants in greenhouses and conservatories can also be affected, so be sure to maintain adequate ventilation to allow free air circulation in hot weather. Also take care not to over or under-water, as both situations will impair the root function and therefore hinder recovery.

As conditions improve, the affected leaves will die off naturally and quickly be replaced with new, healthy shoots.

So now you know how to deal with it, oedema is nothing to fear!

And if you need further friendly, expert advice on this or any other plant condition, then pop in and talk to our knowledgeable staff!