What are saplings?

Saplings are young trees. They can be produced in various ways:

• Through seed
• Vegetative through cuttings

Ad 1: seed

In general seed produces plants that are variable in genotype and phenotype.

• Genotype is the genetic capacity and characteristic of the plant.
• Phenotype is the visible characteristic of the plant

In short we can say that variable populations of plants differ externally in how they look like and differ in their capacities like growth, resistance, fruit production etc. Populations from seed are far more resistant against diseases as a caused by two reasons:

• Through the multiplication by seed, the plants are virus free by nature
• In a variable population plants have variable capacities to protect themselves against diseases. This means that if a disease attacks a population that origins from seed, one plant can die while the other survives as it is less or not sensible.

Go to "Seeds or trees?". Read the text and look at the animation to decide whether to plant seeds or trees.

Ad 2: vegetative multiplication

• Multiply from one plant to a population of many. This can be done through the traditional way of cutting and re-rooting or through tissue (vitro) culture multiplication > with these methods all plants have the same genotype and phenotype. Through selection of the mother plant we can choose a plant that has extra capacities like more production, stronger growth, etc. But they are also very vulnerable for diseases once they have an attack that they have no resistance against. The whole population will die then.
• Multiply vegetative from a variable population of plants. With this method the population is more variable then a vegetative multiplication from one plant, so less sensitive for a disease attack. The advantage is that we can still focus on multiplying mother plants that carry better characteristics than a population that is multiplied through seed.

The vegetative multiplication can be done through roots or stems or (small) parts of them.

Root system

When producing saplings on plugs through seed, a very strong radicle will be formed. This radicle is able to break rocks once growing in them. This is possible because the radicle of a tree is able to develop a pressure over 50 bar (725 psi)! Look at the image of the seed of the oak on the left that’s breaking open by the radicle root. At the seed on the right you see the strong radicle which looks like a nail just a few days old. By putting cuttings on plugs also a radicle is formed, but it is less strong than a radicle developed from a seed, as it’s growing point is mostly divided in a few instead of one. If we multiply saplings based on seed or from cuttings in a plug, we prefer a plug to have the following features:

• At least 15 cm deep so that the radicle is able to develop itself long enough
• Not rounded in order to prevent the root growing in rounds instead of vertical.
  Once growing in rounds it will keep on doing so after planting in this way not being able to penetrate deep enough to search for capillary water
• Enough openings so that the roots have sufficient oxygen to grow well
• Easy working once taking the plant out of them

Once you take the sapling from the plug you should see white tips and a not-divided radicle root. If the tips of the roots are not white, it means that they are infected with a disease like pythium or other moulds. It is also possible that the peat is too salted and root tips have burned.

Not-divided radicle root

During my investigations of roots I found out that in more than 95% of the occasions that people are planting trees or bushes, the roots used for planting are wrong. The reason is that we keep the plants too long in the pot and it causes that the radicle root splits into secondary roots once it reaches the bottom of the pot. There are also industries where the bushes are multiplied with the bare root system. In vines for instance growers multiply their plants in the full ground and once that they are harvested to be transplanted to their final place, the growers clean the roots (and so destroying all the secondary roots) and cut the radicle roots on 5 to 10 cm (2 to 4 inches) length (and so destroying the radicle roots).

So the present multiplying methods cause the destruction of the radicle roots that are able to penetrate deep into the soil with their force of 50 bar (725 psi) and tap capillary hang water. The same methods stimulate the development of secondary roots with their force of 1 bar (14,5 psi) that are unable to do this. This means that we create trees and bushes that are unable to grow without help in dry areas. As a solution for this mistake we use irrigation. So the irrigation that we use is not because the plant is unable to grow on a dry place, but because we do not plant with adequate root systems.

View the images for a good model of plugs and destroyed radicle roots although a big pot was used.

For the more interested reader: some other multiplication methods

There are a few other methods until now not much used in trees.

• A multiplying method through somatic embryogenic regeneration. This is a method for regeneration of plants of trees by regenerating explants of immature zygotic embryos on callus induction medium to grow embryogenic tissue. Culturing of the embryogenic tissue is continued on somatic embryo maturation medium and germination medium. The germinated embryos are further converted to acclimatized plants for field planting. The method is well suited for producing clonal planting stock useful for reforestation. This means that this method results in non-variable populations, making them vulnerable for diseases.
• F1-Hybrids from seed. Through inbreeding various lines of plants are developed. These plants are weaker than their ancestor plants. By combining two inbreeding lines a newly created F1-hybrid line is made of which the descendants have an equal genotype resulting in an equal phenotype. The so called ‘hybrid’ effect results in descendants that can easily be more than 30% bigger than the original plants when starting the inbreeding. This means that these plants produce more food, more biomass or more fruit. In general they are strongly growing but as a result of their non-variability they are vulnerable for diseases.
• Natural inbreeding through seed. There are plants who have a natural inbreeding, for instance tomatoes. For this reason the plants are non-variable and all have an equal phenotype.