Q&As/Plant Diseases or Planter Boxes and Glasshouses/Mouldy Tomato Plants
Why have tomatoes in my polycarbonate glasshouse gone mouldy? The leaves are spotted with mould and turn yellow, and many of the flowers don’t develop into fruit, while my outside tomatoes have done really well.
When it comes to growing plants in glasshouses, ventilation is very important. The humidity can get too high and create mould on both the fruit and leaves of the plants. To avoid this leave windows open all day and close them in the evenings or when the temperatures drop below 18 to 20ºC. Opening the windows does two things; firstly it ensures good ventilation, and secondly it allows insects to come in and pollinate your flowers. Lack of pollination may be the reason your flowers are not developing into fruit. If you want to guarantee adequate pollination without relying on insects, you can hand pollinate the flowers yourself with a small paint brush.
The issue of yellow leaves does indicate a nutritional issue, mainly a lack of nitrogen. Soil plays an important part as does regular feeding. When growing tomatoes in pots always use a good quality tomato mix, or if growing in the ground add in plenty of compost before planting. For strong healthy plants, feed them with a good quality tomato fertiliser every 3-4 weeks throughout the growing period and ensure it is watered in well.