- The height
The leaves of plants, and more particularly of trees and shrubs, are the organs through which the phenomenon of photosynthesis occurs.
• As a rule, the leaves of all woody plants are formed from the petiole (the tail of the leaf) and the blade (the leaf itself).
• Softwoods have very particular leaves called needles, of elongated shape, of semicircular section, with thick wall, whose renewal can take place only after about ten years. This is an adaptation to given climates, and more particularly to the unfavorable conditions encountered in cold and / or dry environments, the needle limiting the evaporation and not requiring significant efforts to the plant for to renew.
• The leaf blade of non-resinous woody plants has very different forms depending on the species. There are simple leaves of linear form, lanceolate, ovoid, cordate, etc., and compound leaves, consisting of several leaflets starting from the same point (for example, the leaves of chestnut).
• On most hardwood species, the leaves of the year fall in the fall to be replaced by new ones in the spring. However, some species retain their leaves in winter, for example, as well as laurel and boxwood. The same is true for most conifers. The great distinction can be made between deciduous trees and evergreen trees. But we must beware of the simplistic classification: leaves = deciduous, coniferous = persistent.
• In fact, all the leaves or needles are deciduous and eventually come off the branch that bore them. By falling back on the ground and disintegrating, the leaf restores to the ground a large part of the mineral salts extracted before. The term semi-evergreen foliage refers to any foliage that falls on the appearance of new leaves. This characteristic is also relative.
The reproduction of woody plants is, in the vast majority of cases, of a sexual nature: a seed is born from the union of a male cell and a female cell. These reproductive elements are formed inside a flower, which is in fact nothing more than an evolution of leaves adapted to the phenomenon of reproduction.
- A flower consists of a chalice, a corolla, stamens and a pistil, when it is a complete flower; an incomplete flower is one that lacks one of these elements.
- The male sex organ is represented by the stamens, which consist of the anther and the staminal net. In the anther is formed pollen, which is released at the maturity of the flower.
- These seeds of pollen (male reproductive cell) will fertilize the eggs contained in the carpel found in the pistil. If stamens and pistils are contained in the same flower, it is called hermaphrodite.
- under the effect of wind - anemogamy;
- or thanks to the transport assumed by certain insects such as bees - entomogamy.
Pollination results in the formation and development of fruit bearing the seeds themselves. These fruits can only interest the gardener if they are consumable or decorative. With regard to the ornamental garden, it should be noted that many trees and shrubs bear fruit insignificant or poor decorative, whose reproductive character remains the only interest. In fact, the reproductive capacity of tree seeds is itself very limited. An example of this is a birch, capable of generating up to one hundred million seeds per season without the risk of seedling growing under its antlers for many years. Only trees with large fruits with their own germinal reserves (eg horse chestnut) are likely to be very prolific.
When it is decided to plant trees and shrubs, it is essential to know in advance the size they will reach in adulthood, for trees, in the twenty to thirty years, and much less for shrubs. This information is usually provided by the nursery catalogs.
Warningfor shrubs, the information often remains below the truth: some subjects, if they are not pruned, can reach a height close to that of trees. As soon as you have accurate information on the size of trees and shrubs, you can determine the ideal location of the plantation in a given garden. Care must be taken to arrange the tallest trees in the garden, and to keep the foreground in the decorative shrubs, not forgetting that a tree or a shrub does not only grow in height, but also in width. It is necessary to take into account for planting spacing two trees planted too close to each other may suffer from their situation as much as a lack of light.
Most shrubs are good for pruning; they can be shaped according to the gardener's wishes. It is quite different for some trees suffer from human intervention, others can not be pruned because of their importance. It is not always easy to predict the shape of a tree in adulthood when planting a subject less than one meter in height (especially if it is a tree with deciduous leaves devoid of foliage at planting time). The shape of the antlers and foliage of a tree, however, remains an essential element for the harmony of volumes in the garden.
Landscapers distinguish the following forms
- slender (or fastigiate): for trees with narrow and cylindrical branches, with fairly free foliage (poplar, cypress, yew, some cedar, etc.);
- ovoid: the antlers form an oblong mass and an oval profile from a straight trunk (birch, oak, beech, linden, maple, walnut, elm, plane tree, ash, pear, cherry, etc.)
- round: the antler is practically spherical from a straight trunk (horse chestnut, olive tree, hawthorn, apple tree, etc.);
- conical: the ant has a conical shape, almost perfect in some subjects, to the point where the lower branches touch the ground and hide the trunk (fir, spruce, certain cypresses, etc.);
- spread: the antler spreads horizontally from a high trunk, dividing into many horizontal branches (umbrella pine, Lebanon cedar, etc.);
- prostrated (or mourner): the end of the branches, very flexible, falls from the top of the trunk down (this form concerns many species, the willow being the most characteristic representative).
This may interest you