Cutting and Pinching, part 1
As home gardeners we pinch and make cuttings, but knowing why plants respond to these procedures can help us improve our techniques and results.
This article explains the physiological changes inside the plants. Later articles will deal with the actual step-by-step process.
Definition of a cutting
"Portion of a stem cut from the parent plant for the production of a new independent plant by inducing it to form shoots and roots under favorable environmental conditions".
When presented like this, it sounds pretty easy to simply induce a plant to form shoots and roots, but what actually happens ? A good place to start is a look at the physiology of a healthy undamaged plant.
Plant Hormones.
Inside a plant, hormones help regulate the growth, e.g. chemicals are transported from one tissue to another which affect the activity of the plant. Two hormones in particular play a role: Auxins and Cytokinins.
Auxins and Cytokinins
Auxins are produced in leaves and stems of the plant, and Cytokinins are produced in the roots. In a healthy undamaged plant their primarily function is to run in a continuous loop and reinforce each other.
Auxins are produced in all buds and leaves along the stem but the largest quantity is produced in the growing point, the tip of the plant. Auxins always travel down the vascular pathways towards the roots inducing them to grow and produce another hormone called Cytokinins.
Cytokinins are produced in the roots in volumes to match the Auxins level. From here they travel back up these same pathways and will prompt the top of the plant to grow.
When the top grows, more Auxins are produced which restarts the process and the plant ensures that top growth is supported by similar root growth and the plant remains in balance.
Apical Dominance
To understand what happens when a plant is pinched we also need to know about Apical Dominance. A typical plant will have leaves formed at intervals along the stem ending in a growing point where the fruit or flower eventually will appear, e.g. a zinnia flower, for example.
In the axis of each leaf (where the leaves are attached to the stem) auxiliary, or secondary, buds are formed. These buds have the potential to become flowers or new growing points, but initially they remain dormant.
When the Auxins diffuse down from the growing point towards the roots, the signal is so strong that it suppresses the auxiliary buds further down the stem and prevents them from developing. Without this suppressing effect the auxiliary buds would elongate and become growing points of their own. However, as long as there is a main growing point these other buds are suppressed. This is called Apical Dominance.
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