Pruning

Plant growth

For a plant to grow, it needs food, water, light and a suitable climate. Plants have adapted to many different living conditions, so their climate needs are very different. But when the basic needs are met, they grow in a fundamentally similar way. This is one of the reasons why they can reproduce according to certain patterns. The most active cell activity takes place in the soft green shoots, where the hormones that stimulate and control the plant's growth are produced. Prolonging growth is, in principle, made just below the topmost top shoot or end bud. This shoot has what is known as apical dominance, which in simple terms means that the top shoot dominates over the side shoots so that the top shoot develops more strongly than the side shoots, giving them more growth power. The hormones go down the stem and limit the growth of the side shoots. The side shoots begin to grow after the top shoot has developed strong growth.

If the top shoot is destroyed, one side shoot typically grows up and replaces the top shoot. However, it is also not uncommon for two or more side shoots to replace the apical dominance of the destroyed top shoot.

Another area of intense cell activity is in the cambium layer - the area between the bark and the wood. It is this layer that enables plants to graft. When two plants are genetically compatible, the cambium layer between the stems can be fused when they are pressed together over a period of time. The growth of the cambium layer makes the stem and stalk thicker and harder, a process called lignification. This process is stimulated by the movement of stem and trunk caused by wind.

How plant growth adapts

The main goal of a plant is to grow to maturity and reproduce (usually via seeds). Many plants then die and they are called annual and biennial plants. Woody and herbaceous perennials often take longer to grow to maturity and repeat reproduction several times. Such plants often develop special cold- and weather-resistant properties to survive. Trees and shrubs develop hard and persistent tissue that can withstand winter cold. The Norwegian cold often kills the softest part of the growth of shrubs in particular, but also some trees. The plants then typically produce new shoots from the harder woody part that has survived, these shoots can flower and form seeds in one season.

Adapting to damage and disease

Plants are often able to limit the spread of disease that most often attacks via the vulnerable softwood growth. It develops natural barriers across the stem via protective chemical reactions, isolating the attack. When the barrier is complete, the isolated part dies and dries out. The insulating process occurs in the cambium layer where rapid cell division takes place, creating scars and callus tissue. The more damage there is to the cambium layer, the longer it takes the plant to heal the wound. Pruning can make a big difference here. You should remove dead branches that may be colonized by destructive organisms that can lead to infections. If a plant has already created a natural barrier between fresh and dead plant material, never cut into the fresh part. However, if the plant is attacked by, for example, canker, the disease spreads so quickly that the plant itself is unable to create a barrier in time. A clean cut underneath all the damage and disease heals much faster than an unclean cut. Never make a cut that is larger than necessary and try to make it where the plant's defense mechanisms work best, just above a node or shoot.

Main principle

The whole plant should be considered before pruning. The most important pruning is the removal of dead, diseased and damaged plant material. This increases the plant's chance of healing and survival. Furthermore, pruning is done to strengthen the plant's supporting structure, to make crops conveniently available, to increase flowering and fruit-bearing capabilities and to stimulate vigorous growth or other desired traits.

Broken apical dominance

When a stem is broken or cut, the apical dominance of the top shoot is broken. Shoots shoot out just below the break point and further down the stem. These latent shoots are often hidden under the bark until they are stimulated to grow. Apical dominance can also be broken if the top shoot is laid or tied horizontally. The flow of sap is reduced and several side shoots develop simultaneously along the main stem. All will grow upwards with relatively equal vigor, and are far more likely to flower and form fruit. This is a great technique for many climbing plants and other long flexible plants.

Impact on the power of new growth

By stagnating growth on shoots via pruning, new growth is stimulated elsewhere on the plant. As a rule of thumb, the harder you prune, the more vigorous the new growth will be - provided the plant is in good health and can tolerate the pruning.

Timing of pruning

Timing is important and directly related to age and flowering. For example, late summer and fall flowering shrubs will flower on annual growth. Early summer- and spring-flowering shrubs flower on the previous year's growth and are pruned after flowering. Plants that bleed after pruning should not be pruned in spring, since the flow of sap is strongest in spring so the pressure will cause extra bleeding. Evergreen plants may produce new growth that is damaged by frost and cold winds if pruned too early in the spring or too late in the summer.

Training of young trees

Trees grown from seed, root cuttings and softwood cuttings will often have one upright shoot with an end bud. A hardwood cuttings typically develops its top shoot from the uppermost lateral bud, if you only want a trunk, lower shoots are removed. Many varietal trees are developed via grafting, the point where the graft and rootstock meet is often visible with a swelling. A tree that has been grafted via tile germination will have growth in the form of a single shoot from the grafting site. Shoots from the rootstock or roots must be removed. The top shoot will develop from the top leaf node on the scion as with hardwood cuttings. Shoots below the top shoot should be pinched if a single stem is required.

First year training

First year growth will sometimes have leaves and small shoots growing out from the main stem. These should NOT be removed unless they are diseased or dying, as the tree needs all available leaves to build up further growth. During the first winter, a healthy tree rarely needs pruning, but weak and strange-growing shoots can be pruned. If the top shoot is weak, the main trunk can be pruned back to a strong shoot. The tree does not need staking unless the trunk is weak and unstable. If the tree is staked, give the trunk plenty of wiggle room to sway in the wind. Also take care not to damage the roots with staking. Strong side shoots that threaten the dominance of the top shoot must be shortened or removed. If the top shoot is broken and several side shoots are competing to replace the top shoot, select one that can take the role and prune the others.

Second year training

Strong side shoots are developed. Only remove dead, damaged and diseased growth, and any shoots that compete with the top shoot.