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It’s a new term at college and time for Astrid Aspidistra and her friends to return to the classroom where she normally lives. Like any class pet, she and others came home with me for the summer holidays. At the end of the last term, I packed all the classroom plants into the back of my car so I could look after them during the summer break. And so it was, on the hottest recorded day ever in Scotland, I took them out of the car, sat them on the wall in front of my house and promptly forgot about them for two days. By the time I remembered to move them into the shade, it was too late for poor Astrid. She already had a bad case of sunburn.
I rescued Astrid a few years back from underneath a greenhouse shelf where she had been all but forgotten. Her leaves were badly damaged by slugs and snails and, being a slow-growing plant, she still bears the scars. She now lives in one of the horticulture classrooms where I use her to demonstrate, amongst other things, the parallel-veined leaves which prove she is a monocotyledon. In the shady classroom, she is right at home and, since I placed her there, she produced two nice fresh leaves, free of slug scars. Unfortunately, those new leaves took the brunt of the sun damage.
Astrid is a shade plant and, because of that, it is safe to assume she has a relatively low light compensation point. A plant’s light compensation point is the point at which the amount of energy gained through photosynthesis is the same as the amount of energy and carbon dioxide consumed, or lost, by the plant in order for it to grow. It is similar to our calorie requirements. If our calorie intake is lower than the amount we need for day to day activities, we lose weight. If it’s higher, we gain weight. During the growing season, all plants prefer an amount of light that is higher than their light compensation points so they can put on a good amount of weight, but too much sun can cause significant damage, especially for shade-lovers like Astrid
Like most shade lovers, Astrid has large leaves and those leaves are dark green and rich in chlorophyll. This allows her to capture as much sunlight as possible and makes her ideal for a shady spot in warmer climates, or as an indoor plant in cooler climes. It does not, however, make her a good candidate for full sun at the height of summer. Under normal circumstances, sunlight hits the leaves of plants and excites the electrons in the chlorophyll, creating the energy plants need to complete the process of photosynthesis but too much excitement can cause the cells to break down. In Astrid’s case, with her lower light compensation point, she over-photosynthesised, used up too much carbon dioxide and this caused dangerous levels of oxygen to build up, killing some of the cells in her leaves.
Sadly for Astrid, there is no cure for her sunburn and, because she grows so slowly, she’ll bear the evidence of my mistake for a long time. She is currently recovering in a cool, shady spot in my house and soon, she’ll return to the classroom where she’ll be able to help me teach my students about the perils of putting plants in the wrong position.
The Plant Listener
Explaining the processes upon which all plants rely for their survival and how we can use that knowledge to influence our horticultural practices
Available in paperback and kindle from Amazon
ISBN No: 978 1 9997243 0 6