Alternation (fruit growing)
Under alternation refers to the fluctuation of the fruit yield in the biennial rhythm of fruit trees , especially when Apple tree and Pear tree and to olive trees and plums , often triggered by influences of the weather.
With apples, this leads to the so-called "apple years", which alternate directly with years of very low yield. Without horticultural intervention, this would make fruit growing unprofitable, since in the apple years many, but relatively small, fruits bring in little profit with increased supply, while in the following year with lower supply, high prices can be achieved, but only little fruit can be sold.
The apple varieties Boskoop , Delbarestivale , Edler von Leipzig and Elstar are particularly susceptible to alternation .
procedure
The seeds and also the still growing shoot tips of many fruiting trees form plant hormones ( phytohormones ), which reduce or prevent flower bud differentiation for the following year if the tree has too many or too many flowers . Then little or no flowers are planted for the following year. In contrast, in a year in which the tree has no or hardly any flowers, a relatively large number of flower buds are created for the following year.
Since the biomass that a tree can generate from the assimilates (energy sources) available through its metabolism is limited , in a year with a large number of fruits these will be smaller on average. On the other hand, a tree can invest more energy in a year with only a few fruits in order to create new branches and thus flower buds and to let the individual fruits ripen relatively larger.
Occur
The occurrence of alternation is an individual expression of the metabolic balance of each individual plant. Nevertheless, apple years usually occur in an entire region, for example a late frost in one year triggers the alternation for almost all trees at the same time through a strong reduction in flowers. The second year will be “apple year” for the entire region.
This in turn means that the number of new shoots and buds falls below the average, so that the third year will again be a low-yield year. This change only weakens with time, unless it is in the apple year by engaging the gardener or tree warden broken.
Intervention options
An even yield is desirable in fruit growing.
In some varieties, the formation of flower buds is inhibited for a long time by hormones. The flower buds then differentiate at a late date. With such varieties, early hand thinning of the fruit can encourage a stronger set of flower buds for the next year. With other varieties, the flower buds for the following year are already created a few weeks after flowering. In this case, the number of flower systems for the following year cannot be increased by thinning the fruit.
Too large a quantity of fruit can largely be avoided by appropriate pruning , poor fertilization or early chemical or mechanical thinning of the resulting fruit.
Alternation with the olive
In the case of apples and pears, the alternation affects the whole tree, whereas in the case of olives only the bearing branches, while the non-bearing branches start to bud in the next year. For this reason, experienced olive growers cut their trees as soon as they are harvested by cutting away the branches that have carried them as far as it makes sense and leaving the others standing so that they can carry them for the next year.
literature
- Gerhard Friedrich (ed.): Physiological foundations of fruit growing . Ulmer Verlag, Stuttgart 2000, ISBN 3-8001-3475-6 . Pp. 212-220.