Text and photo: Christine Wiemann

People like me who loves the greenhouse has at least one yearly task that is boring – cleaning the greenhouse. In fact, this task should be done twice a year if you want to cultivate all year round. In April I thoroughly clean the greenhouse. Before autumn begins in September, I clean it again. After I have cleaned, the winter cultivation can begin in the greenhouse. I have stopped using soap when cleaning. Why? Find out in this article.

Why cleaning in autumn?

We all know it. A greenhouse is the prettiest when it is clean inside and outside. Although autumn cleaning is not just about how it looks.

• Clean glass panels improve the light conditions for winter cultivation
• The light transmission of clean glass is 85-90 percent
• Cleaning the greenhouse removes pests, that could be a threat to your winter cultivation

Climate change has a big impact

The climate change has made it possible to cultivate in the greenhouse all year round. On average, the climate is a few degrees warmer than previously. This also affects the pests in the greenhouse. Therefore, more types of pests can be active throughout the greenhouse year e.g. aphids. A warmer climate also means that pests will become a bigger problem. Usually, it is the temperature that controls the reproduction speed. The warmer it is, the more pests there will be.

Autumn cleaning

Pests multiply slower during winter, therefore, the cleaning of the greenhouse does not have to be as thorough as it is in spring. Many people may still have tomatoes, chillis and cucumbers in the greenhouse. Let the plants stay and clean around them.

Step 1

• Remove old plants from the greenhouse
• Wash shelves and pots with clean tap water
• Remove plant residues e.g. withered leaves
• Tidy up

If there is anything left from an old plant, it may have fungal spores and bacteria which can hibernate for the winter. If these are not removed, they may spread and attack the new plants.

Step 2

• Wash your greenhouse on a cloudy day
• Fill a bucket with water (preferably rainwater)
• If you want you can add 1 to 2 dl of vinegar (it removes the calcium)
• Use a soft brush and a good sponge
• Get into all the nooks and crannies in the aluminum glazing bars
• Wash down the greenhouse with a hose pipe at high speed

Soaps for cleaning

All chemical soap products for the greenhouse effectively kill pests. These soaps also effectively clean the horticultural glass. As previously mentioned, clean glass have a light transmission of 85-90 percent, and even though the glass may look clean by the end of summer the light transmission may be reduced by 50 percent. This will especially affect your winter cultivation if the horticultural glasses are not cleaned.

But are soaps and other chemicals even necessary?

No. But with a soft brush and some clean water, the horticultural glasses can get just as clean as if you had used soap. If there is calcium on the windows, you can add some vinegar to the water.

No matter what, the pests will get inside the greenhouse at some point. The pests live in the surrounding nature. But remember, pests are not the only animals that get inside the greenhouse. So do the natural enemies of pests. These we call useful animals.

If we do not use soap, there will be an equal balance between pests and useful animals. Here the useful animals will keep the population of pest down. As soon as we wash the greenhouse down with water and soap, we do not only kill the pests but also the useful animals. Therefore, by only using water we disturb the natural balance as little as possible.

The truth about chemical products

Soft soap is the most recommended product for cleaning the greenhouse. In fact, soft soap is not good for the aluminium. There are a lot of cleaning products where it says: “greenhouse cleaner”. These products contain potassium hydroxide with various soaps, surfactants and one product contains benzalkonium chloride. What they all have in common are that they are effective, but not harmless. It is recommended that protective equipment is worn to protect the skin etc.

We do not know the consequence for using soap products in a hobby greenhouse. There are no studies on how much of the soap products that end up in the plants and in the crops we eat.