Planting trees

The right time to plant a field-grown tree is during dormancy. For deciduous trees, this is from the time the trees have dropped their leaves and hardened off until sap flow starts again in spring. In Western Europe, balled-and-burlapped trees can generally be planted from mid-November until the end of April, but this depends greatly on climatic conditions and the tree species. Temperatures in fall and spring play an important role, and not all trees drop their leaves at the same time. The same applies in spring to the time at which the leaves develop. The planting season for evergreen and coniferous trees is generally somewhat longer than for deciduous trees. Container-grown trees can be planted year-round. These are generally smaller tree sizes.

When should trees be planted?

Fall is the ideal time to plant trees. The tree’s establishment in its new location is determined by the extent to which it develops new feeder roots. This depends on several factors, such as soil moisture content and soil temperature. In fall, these factors are generally favorable. Soil temperature is still sufficiently high for trees to develop new feeder roots after transplanting and before winter sets in. The increase in the number of feeder roots makes water uptake easier the following spring. The trees experience less transplant stress and will resume growth more quickly. Planting trees in fall is therefore ideal, but not always feasible in practice.

Planting trees: Complete step-by-step guide

This step-by-step guide explains how to plant trees efficiently and effectively. From digging the planting hole to pruning after planting, we cover everything you need to know to ensure newly planted trees establish well and can grow vigorously in the future. This guide provides the information needed to plant trees successfully.

1. Planting trees: digging the planting hole

Dig a generous planting hole with a diameter 1,5 to 2 times the diameter of the root ball. For example: if the tree has a root ball with a diameter of 60 cm, the planting hole should have a diameter of at least 90cm, but preferably 120cm. Make the planting hole slightly less deep than the height of the root ball. To allow for oxygen exchange, the tree must never be planted deeper than it stood at the nursery! With large trees, allow for settling due to the weight of the root ball. This can compact the soil beneath it, especially if the soil has not yet settled properly, for example on new construction projects (fig.1). Loosen the bottom of the planting hole thoroughly, to a depth of 1 spade, and loosen the sides as well if necessary. The sides of clay or loam soils can become smeared during digging, especially when wet. Loosening them with a spade allows the roots to grow through more easily. Mix any new soil with the existing soil. Sometimes the hole is filled with garden soil. Mix this with the existing soil at the bottom so that the roots can grow out of the planting hole more easily.

2. Planting trees: anchoring trees

A newly planted tree must be anchored to prevent it from being blown over. The most commonly used anchoring method is above-ground anchoring with two or three stakes. Two stakes are sufficient for smaller trees, up to a trunk circumference of 25-30cm. Larger trees, with a trunk circumference from 25-30cm, are preferably planted with three stakes. Choose stakes with a length and thickness appropriate to the tree size. For standard trees, with a clear stem height of min. 200 cm, use tree stakes of 250 cm. 100 cm goes into the ground and 150 remains above ground. For a shorter stem length, choose a shorter stake.

Using a soil auger, drill 2 or 3 holes in the ground immediately beside the root ball, opposite each other or in a triangular arrangement, and drive the tree stakes firmly into the ground. At least half of the stakes should be below ground. When using 2 stakes, consider the prevailing wind direction. In the Netherlands, this is the southwest wind. In that case, place the stakes to the southeast and northwest. Backfill the planting hole with soil. Soil life can be stimulated by mixing an organic soil amendment or well-decomposed compost into the soil. Firm the soil in the planting hole thoroughly as you go. Connect the tops of the three tree stakes with crossbars to form a sturdy frame.

This is not necessary when using two stakes. Place a tree tie around the trunk from each stake and nail it to the tree stake. The tree ties should not be loose, but they should not be under tension either. After approximately 3 years, the tree stakes will have deteriorated and the above-ground part can be removed. The tree will have anchored itself sufficiently to continue growing without support.

3. Planting trees: creating a watering berm

Newly planted trees need extra water for at least the first two years. The amount depends on the weather and the tree species. Use a watering berm made of soil or plastic to ensure that the water soaks well into the root ball. The diameter of the watering berm should equal that of the root ball, so that the water also penetrates the root ball (figure 5). In dry weather, check the moisture level next to the root ball 1 x per week and water as needed. When water is needed, apply a large amount at one time rather than a little every day. Soil moisture can be checked, for example, with a soil probe or by pushing a spade into the ground. Keep the root balls moist throughout the growing season, but not soaking wet! Trees can also die from too much water; there will then be too little oxygen in the soil and the roots will rot. In addition to a watering berm, there are other methods for watering trees.

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Pruning after planting

Healthy trees have a natural balance between crown and roots. This balance is disturbed when the tree is dug because every tree inevitably loses part of its roots during digging. As a result, the roots can supply less water to the crown, which causes stress. The tree will respond by producing fewer and smaller leaves, thereby reducing its leaf surface area. When the water shortage is too great, the tree will even shed wood in the crown, with the risk of affecting its growth habit. Watering is therefore necessary for the first two years, but this alone is often not enough. During long warm periods or at extremely high temperatures, leaves may dry out even though the root ball is moist. The root capacity is then simply insufficient to transport the required amount of water to the crown. Applying more water is not an option in that case and will only have adverse consequences such as oxygen deficiency and root rot. The only solution is to reduce the need for water by pruning the tree. Preferably immediately after planting, to prevent the trees from suffering severely during peak periods. During the first two years, the crowns will therefore have somewhat less volume, but the trees will experience less stress, establish more quickly, and develop better afterward.

Pruning is carried out in one- or two-year-old wood. The thick wood in the crown must be retained. It contains reserve nutrients that the tree needs to develop new roots. It is not necessary to prune all the existing one- and two-year-old wood from the tree. Trees with a great deal of wood in the crown need substantial pruning, but trees with little wood in the crown, such as an Ailanthus, are pruned minimally. To avoid adversely affecting the tree’s growth habit, it is advisable to retain the terminal buds and remove only lateral shoots.

Trunk protection against sunscald

Unfortunately, it is becoming increasingly common: cracks in the trunk caused by overheating. Water transport in the trunk normally protects the cells of the bark from overheating, but after planting, less water is transported to the crown and this cooling system does not work sufficiently. The trunk is therefore at risk of sunscald. The setting sun is the main culprit because it shines perpendicular to the trunk and can heat its cells so intensely that they are damaged. This is why sunscald is usually visible on the west side of the tree.
Trees with smooth, thin bark are particularly vulnerable and must be protected. This can be done by wrapping the trunk with coconut fiber or reed mats. Trees with rough bark and trees that branch from the base are less vulnerable and generally do not need protection.

Please note: burlap was often wrapped around the trunk in the past, but experience has shown that this can have adverse effects. Because the burlap is wrapped tightly around the trunk, heat can build up underneath it. The temperature can then rise considerably, with negative consequences for the bark and the rest of the tree