Science in The Garden
September 1, 2020

In this article, we will have a look at sunlight and leaves, plant propagation and genetics. And why these things are important to us gardeners in order to get the best out of our plants.


Question: Does sunlight make plants grow?

No it doesn’t. It actually slows growth down. Your own experience will confirm that. If you put a pot plant on a window sill it will, of course, grow towards the light, but why? Plant growth is controlled by a number of hormones that are produced close to the tip of every growing shoot. If you shine a light on one side of that shoot the light destroys the hormone on that side but not on the other. The result, the growth on the shady side overtakes the growth on the sunnyside and the stem bends to the light.

A second example just to make the point. If you leave potatoes in a dark vegetable drawer, they will, as we all know, produce long white shoots. The light has not been able to slow the growth down.

Plants have evolved to cope with the light level they prefer. Putting a shade plant in full sun isn’t a good idea. Nor the other way round.


The colours of leaves are caused by pigments, mainly chlorophyll (green), xanthophyll (yellow)and carotene (red/orange). Years of plant breeding has produced plants with a range of colours and variegations not normally found in nature. However, this change of the natural pigmentation of the leaves has consequences. The golden leaved form of Philadelphus (mock orange) is a beautiful and graceful shrub. We find it tricky to place because too much shade and it starts to go green and too much sun scorches it. This is because it does not have the full natural complement of pigments in its leaves.

So if you are going to buy what could be an expensive, beautiful plant please check with the garden centre staff the conditions it prefers.


The two main ways to produce more plants are from cuttings and seed. Seed is easy to collect and some will germinate and flower just like their parents. However, some of your carefully tended plants will not.

If you have ever tried sowing Lupin seeds collected from plants in the garden usually the next generation has a lot of blue flowers. Crocosmia “Lucifer”, on the other hand, will produce almost all the same coloured flowers as the parent. Why? When a plant produces seed the characteristics of the parents (the genes), are shuffled like cards in a deck. It’s a complicated process but the idea is a simple one. That shuffling means that the offspring have not been dealt the same cards.

We all know red-haired children whose parents both have dark hair. But red-haired parents can’t have dark-haired children.

Its genetic instability eventually leads to all self saved Lupin seeds turning blue. Crocosmia “Lucifer” seeds are much more stable. But don’t let all that stop you from having a go. Seeds bought from a garden centre will have been professionally produced to remove as much of this instability as possible.
No such shuffling takes place with cuttings because the new plants will have exactly the same characteristics as the parent plant.

The plants that make our gardens are an unnatural collection from all over the world. They have evolved and adapted to the conditions in their own country. Not only that many have been bred here to enhance some of their characteristics meaning they are not natural. So knowing the conditions that a plant like means that we can get the best that they have to offer.