Grow Three Plants Outdoors: Part 8: How to Protect Plants from Rain and Mould

The second half of summer is the most exciting part of the year for outdoor growers, due to the unpredictable weather. In good years, when there is plenty of sunshine and warmth, hopes of a beautiful harvest increase. Conversely, when the weather is rainy and cold, the plants’ metabolism slows down and there is a greater risk of mould. In today’s instalment of our outdoor growing series, we will look at how to protect plants from rain and mould.

In the previous instalment, we discussed fertilisers and nutritional supplements to support flowering. We also showed you how to protect plants from the wind and talked about the dangers posed by male plants and hermaphrodites. If you are growing photoperiodic varieties, your plants should be in full flower during September. Flowering plants are most often affected by mould, which can easily deprive you of your entire harvest. What can you do to prevent mould from affecting your garden?

Mould on plants and how to combat it

Although there are many types of mould that attack plants, most growers are likely to encounter two species in particular – powdery mildew and grey mould, which causes flower rot. Both most commonly attack plants during flowering, but they manifest themselves in very different ways.

Powdery mildew manifests itself as characteristic white spots that appear on the leaves and is caused by parasitic fungi from the Erysiphaceae family. Plants affected by powdery mildew look as though someone has dusted them with icing sugar, and the infection most commonly first appears on young leaves. It is difficult to get rid of powdery mildew completely, especially during flowering, when some types of fungicide cannot be used. However, there are safe sprays that protect plants against mould or at least slow down the infection and allow them to mature.

Canna Cure: A universal protective spray effective against pests and fungal diseases, including powdery mildew, which can also be used during flowering. In the event of an infection, apply the spray every three days until the symptoms are suppressed, and then once a week as a preventative measure.

BioBizz Leaf Coat: A universal protective spray based on natural latex that is effective against mould and pests. Leaf Coat is non-toxic and can be used during flowering; however, its use should be discontinued approximately two weeks before harvest. Use the spray preventatively and, in the event of an infection, twice a week.

Purolyt: A disinfectant concentrate based on hypochlorous acid (HOCl) with a biocidal effect, which leaves no residues behind and is also safe for flowering plants. To treat an infection, mix 20 millilitres of Purolyt into 1 litre of water and apply the spray every 2–3 days; after the symptoms disappear, apply it once a week as a preventative measure.

Grey mould is caused by the fungus Botrytis cinerea, which mainly attacks flowers. A major problem with botrytis is that flowers very often begin to become mouldy from the centre, making it difficult to notice the infection in time. Noticeably dry leaves and bracts on otherwise green flowers may be a warning sign. Grey mould cannot be eliminated, and it is best to harvest affected plants as soon as possible. Throw away mouldy flowers and under no circumstances consume them.

The best protection against botrytis and powdery mildew is primarily prevention in the form of sprays. It is also important to ensure that all parts of the plants are exposed to air and that permanently damp areas do not develop in the crop. For this reason, plant them sufficiently far apart and prune them regularly. A makeshift shelter that protects the plants from rain may also be beneficial.

You may be interested in: A detailed guide to getting rid of mould on plants

That is all for today. In the next instalment of the Grow three plants outdoors series, we will look at how to tell when plants are ripe for harvest and how to prepare for it.