Growing your own in the controlled environment of a greenhouse or polytunnel has its obvious advantages but it has some challenges too. Controlling temperature, watering and humidity control as well as pollination can be a challenge at times. Providing humidity is important in pollination to avoid dry set. Fruiting crops like tomatoes, peppers and melons need successful pollination in order to set flowers and produce fruits. Tomatoes and peppers are self pollinating, meaning that one flower contains the necessary pollen. Squashes and melons have male and female flowers, so you have to make sure that the pollen from the male flower (which usually have a longer stalk) reach the female flowers.
Assisting pollination in your greenhouse is easily done just by keeping the vents and door open, but in areas where bumblebees and other beneficial insects are rare (yes there are places like that), you might need to do the pollination yourself. Bumblebees are the most effective pollinators of tomatoes for example, as tomato flowers need slight movement so that the pollen falls from the stamens to the stigma of the flower. You can simply tap the tomato plants to help this, but as you can imagine the bees do a much better job of it. They grab the staminal tube of the flower with their jaws and set the whole flower into vibration by activating their flight muscles.
Tomato flowers don’t contain nectar so it is important to plant nectar rich flowers around your greenhouse to attract the bees, as they need the protein from the tomato flowers and high sugar content nectar too to feed. So flowers are an important part of the garden, not only they look pretty but they will help you to achive the perfect pollination too! Bumblebees are most active at the temperature of 15 – 25 Celsius, so it is important to open your greenhouse in the summer in the morning and evening too.
Commercial tomato growers use bumblebee hives to pollinate their crops in the massive greenhouses and polytunnels across the world.
So to continue... Spring Onions... As I said in the part 1 we love our onions. As well as the normal onions I also have a small bed of multiplying onions...