Science of Gardening

Each time we take a cutting to propagate a favourite plant we are doing an experiment, testing the hypothesis that a cut shoot will reorganize its tissues to form roots, enabling a plant to grow. If we take more than one cutting, to maximize our chances of success, we are replicating the experiment in accordance with scientific method. And if we treat half the cuttings with hormone rooting powder, to see if it promotes tissue reorganisation and rootlet formation, we are adding another treatment to the experiment. If the cuttings root, we might next formulate a new hypothesis about how cutting stems stimulates the production of hormones, which in turn stimulate previously quiescent cells to divide and form roots. However, we need sophisticated equipment to test this hypothesis, so for most of us the experiment finishes when we pot up the new plants we have produced.

Almost every manipulation we carry out in the garden reveals something of the scientific process underlying the growth of plants – including, of course, weeds. When we dig the vegetable garden, and find it covered with unwanted seedlings a few days later, we realize our soil contains seeds of many weed species, dormant until we disturb them and expose them to light. This light stimulation induces germination, a perfect mechanism for ensuring that weeds only grow when the soil has been disturbed and is therefore suitable for seedlings to become established and form a new crop of seeds. When we prune the roses, we do so to divert nutrients to the shoots we wish to grow strongly and produce flowers. Similarly, we reprogram growth patterns when we prune apple trees or disbud chrysanthemums to ensure one large bloom is produced, rather than many smaller ones.

And while we are on the subject of chrysanthemums, remember that they do not flower until the Fall. The flowering of many species is controlled by daylength. A pigment called phytochrome enables the plant to measure the relative lengths of night and day and ‘tells’ the plant when it is ‘time’ to flower. Chrysanthemums are prevented from flowering in long days, and only released from inhibition as the daylength declines towards the Fall. Other plants, like carnations, flower in long days and yet others, like biennial walflowers, can react to temperature and require the stimulus of a cold shock to make them flower. All plants have mechanisms for reading the seasons and even telling the time, so that they flower at the optimum time for pollination and seed set, and can fit their life cycles into appropriate ecological niches, where there is a minimum competition from other species for space and light.

So most bulbs flower in the spring, using nutrients stored since last spring in bulbs or corms. This pattern evolved in the wild and allows woodland bulbs such as hyacynths, for example, to take advantage of the season when trees are leefless, harnessing the energy of sunlight before intense shade develops to produce a new store of food to carry them through the summer.

And when summer is over and we throw debris on the compost heap to rot down, we initiate a whole chain of complex processes. In the compost microbes such as fungi and bacteria secrete enzymes that break down the dead plant tissues, releasing from them the sugars the microbes require for growth, and other nutrients that can be returned to the soil. The dead bodies of the microbes also decay and add to the store of nutirents in the new soil being produced. During these processes heat is generated by the respiration of the microbes, giving the compost its characteristic warmth, and carbon dioxide is released into the atmosphere. When we spread compost on the garden in the spring, to feed our newly planted vegetables, we contribute again to the process by which nutrients and carbon are being cycled all the time, in nature.

As a gardener I enjoy creating a place that is quiet and peaceful and I get a thrill from observing and identifying the continual restless energy of the scientific processes that make this possible. Watch them yourself as you garden – they’re fascinating!