David Beeson, 26th October 2021
The Hillier Garden, near Romsey in Hampshire, is owned by Hampshire County Council and is a gem of a botanic and popular garden. The site was originally the home of Sir Harold Hillier, who established the small but, up-market, garden business that wins gold after gold at the Chelsea Flower Show. These gardensshould be on everyone’s ‘go to’ list, not only for the trees but also the huge herbaceous border, winter garden and the conserved native wildlife – including good numbers of orchids. The popularity of the site can be assessed by the THREE eating spots, including a distinctly good formal restaurant. (Yes, we did sample.)
It is an all-year location with a large Winter Garden with solid all-weather paths.
With November fast approaching the autumnal colours are developing, yet slower this year than perhaps I might have expected. Witch hazels, dogwoods and liquidambers were especially colourful, and their reds and oranges contrasted with the range of other foliage colours.
We all fall into the rule that leaves are green. Of course, that is far from the truth and gardeners use the range of foliage colours to paint a ‘gardening picture’ as much as can be achieved with flower impact.
Leaves are light energy harvesters. Photons arrive from the sun, and through photosynthesis, can have their energy trapped into chemical bonds. It is never going to be 100% efficient, so the leaf inevitably warms up. Once dropping light levels, and possibly temperature, mean that the process is no longer efficient the leaves may need to be shed. [Warm climate plants ( and species like the hollies and evergreen conifers) can hold their valuable leaves for many years, yet even then shaded leaves will be discarded.]
To harvest the maximum amount of energy will ensure a range of photosynthetic pigments will need to be manufactured, each absorbing a different spectrum. Those pigments will change with the quality of the available light, for example, the spectrum of light reaching beneath a canopy will not be the same as arriving there.
There are four main pigments: Chlorophylls A and B (green to the eye), Xanthophyll (yellows) and Carotenoids (oranges). Chlorophylls are dominant yet break down first, exposing the underlying pigments.
There are also anthocyanins; these are intense red pigments that aren’t made during the summer, only appearing with the final group of the autumnal colours. These molecules also give the red hue to apples, cranberries and raspberries.
EXPERIMENT: extracting photosynthetic pigments.
- Collect a range of leaves of different colours.
- Cut with scissors and crush them with mortar and pestle.
- Cut blotting paper or thick paper towels into circles that overlap Ramekin dishes. Cut a slot to fold down, like a tongue, into the dish’s base.
- Extract the leaf pigments by mixing the crushed material with isopropanol (an alcohol), which can be bought on the Internet. Extraction will take only a couple of minutes.
- Using a fine tube or wire or toothpick or similar, add small quantities to the centre of your circle. If possible, dry with a hairdrier (but avoid splattering the extract.). Make a concentrated spot, with a ‘more-the-better’ attitude.
- Add the alchol to the dish, locate your circle and push tongue into the alcohol. Sit back and wait about 30 minutes.
- The isopropanol will run up the tongue, meet the concentrated extract and spread out over the circle. The pigments do not have the same solubility and will move at varying speeds. You will see the different pigments, especially if the paper is dried.
- By now you will have guessed that these or similar pigments are found eleswhere in the plant kingdom. You may wish to explore carrots, beetroot or rose petals.
It is possible to re-extract each pigment from your chromatogram and check how each absorbs the colours / wavelengths of light. This is shown below. You will see that green light is poorly absorbed. It is not used in photosynthesis and is either reflected or passes through, ensuring plant leaves often look green.
If you are given a horrid plant that you want to kill, but it must appear you are looking after it … leave it in green light! Photosynthesis cannot use green light and your plant will die.
Photosynthesis uses mainly blue and red light. Green is wasted.
Now some images from Hillier Garden.
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