• The planting season
• Trees and bare-root planting stock
• Root-balled trees
• Trees in Air-Pots® or spring rings
• Advantages of the Air-Pot®
• Finishing the root ball after planting
• Non-biodegradable acrylic mesh cloths
• Root balls wrapped in coconut matting
• Pruning when planting
• Improving the planting hole with fungus-dominated humus compost
• Planting height: neither too high nor too low
• Filling the planting hole in three steps
• Damage during planting and wound care
• Root ball size
• Installing tree stakes
• Introduction to tree anchoring
• Above-ground anchoring
• Underground anchoring
• Crown anchoring
• Protecting the tree trunk against bark scorch
• Choosing tree stakes: wood type and length

The planting and lifting season for trees begins when they shed their leaves in autumn and ends when the new buds start to swell in early spring. We call this the dormant period, which runs roughly from early November to the end of March. Exceptions to this are a number of specific species and evergreen trees. There are also times when lifting and planting cannot take place. As a rule of thumb, to protect the tree and the soil, we apply the following:

-Trees are not lifted or planted when there is snow on the ground or frost in the soil.
-Trees are not planted when the ground is so saturated that water stands in the planting hole.
-Trees are not planted when there is a risk of damage to the soil structure.

Root-balled trees are what we trade most, and one of their major advantages is that the roots do not dry out quickly, which means the shock of transplanting is less severe. Especially in the case of large trees that have been transplanted several times, a good root ball is crucial for successful establishment. If the tree has a girth size of 16–18, it will almost always have a root ball. Even if the tree remains above ground for some time before transport and planting, and the planting is not carried out properly, a root-balled tree can still survive reasonably well. It is, however, important that the tree has been transplanted several times, especially in the case of large trees. This repeated transplanting during the growing process is necessary to create a root ball containing many fine feeder roots, keeping the tree adaptable and transplantable. As long as we continue transplanting a tree at the nursery, it remains transplantable and therefore saleable. The aftercare of root-balled trees after planting is also less intensive than that of bare-root stock. Whereas our advice is to plant bare-root plants preferably in autumn (late October / mid-December), a root-balled tree can be planted over a much longer period.

A few important reasons to choose a tree with a root ball:

Anchoring: A tree with a root ball stands more firmly in the ground immediately after planting, as the roots remain connected to the soil within the root ball. A bare-root tree always stands less firmly; when the new roots start to emerge during establishment, wind can cause slight root movement, which may break the young root tips. The larger the tree, the greater the effect of wind. With a heavy root ball at the base, the tree can also be anchored underground effectively, simply by tightening straps over the root ball.

For some trees, it is also important that certain soil fungi are carried along, the so-called mycorrhiza. This is a symbiosis between soil fungi and the root of the plant and occurs directly around the roots of the trees. These are essentially fungal threads that enable the root system to absorb nutrients as efficiently as possible. The symbiosis lies in the fact that, in return, the plant supplies sugars and other carbohydrates back to the fungus. The tree produces these substances through photosynthesis in the leaves. For a number of tree species, the presence of mycorrhiza is of decisive importance for successful establishment. An example of this is common beech (Fagus sylvatica) and Acer palmatum, which also depend on certain trace elements. The fungal threads also increase the root surface area, which is essential for good moisture uptake.

A final advantage is that root-balled trees also dry out less quickly during transport and storage, because moisture is retained within the root ball.

It may happen that a planting project has to be postponed while the trees have already been lifted and are lying at the nursery. In that case, an Air-Pot® is an ideal way to continue growing the trees above ground for a season. The use of Air-Pots®, also known as spring rings, is therefore mainly seen during the growing season before a tree is planted. This method is primarily aimed at allowing a tree to develop a good root system while it is above ground. An Air-Pot® also creates an extra layer of soil around the root ball in which the tree can root, while buffering nutrients and moisture. The tree should preferably be placed in an Air-Pot® before the leaves emerge, because once the leaves appear, root activity also begins. The earlier the tree is placed in an Air-Pot®, the stronger the root system will develop. It is essential to place the tree in the Air-Pot® in the location where it is to remain for the rest of the season. If you move a tree in an Air-Pot®, there is a very high risk that the vulnerable root system will break. The tree must also remain in the spring ring for at least 3–4 months in order to achieve full rooting that is strong enough for planting. During the growing season, the tree must be supplied with water daily by means of drip irrigation. Once planting is due to take place, it is advisable to enclose the tree in a wire basket as soon as the Air-Pot® is removed. This basketting ensures that the entire root system remains intact and distributes the loads during underground anchoring.

A major advantage of the Air-Pot® is that it can easily be made to any required size, unlike a normal pot or container, which has a fixed size. In addition, an Air-Pot® is designed to encourage the tree to root outwards as much as possible, and air pruning creates a finely branched root system. This is achieved because the structure of an Air-Pot® consists of inward- and outward-facing cones that guide the roots outwards. This prevents roots from circling, unlike in a container, with all the associated disadvantages. The cones are open on the outside, so as soon as the roots grow through them, they die back under the influence of light. Growing a tree in an Air-Pot® is more labour-intensive than planting root-balled trees during winter dormancy, but it can be a good way to allow a tree to continue growing above ground over the summer season.

In exceptional cases, we can place trees in Air-Pots® on behalf of a client and only deliver them at the time of planting. Please ask your contact person about the additional costs.

After the tree has been placed in the planting hole and secured with underground anchoring, the finishing process can begin. This simply involves filling the planting hole with the planting soil. To ensure that the soil settles properly and that no air pockets form around the root ball, the soil should be firmly compacted by foot. Watering afterwards is essential, as it not only helps the soil make good contact with the root ball but also allows it to settle immediately.

When the tree was lifted from the nursery, the root ball was wrapped in burlap and fitted with a tree basket made of reinforced steel wire. The brown-colored burlap is a completely natural product and decomposes quickly, usually within one to two months. The wire basket is made of steel wire and will eventually decompose as well, although this will take several years due to the nature of the material.

One advantage of this in combination with underground anchoring is that the anchors rest against the compact root ball. If the wire basket is positioned against or very close to the tree bark, the wire can be cut at that location to prevent it from growing into the bark.

In some cases, we come across blue jute cloths. These are jute-acrylic mesh cloths. They consist partly of natural jute and partly of synthetic thread (acrylic). This type of wrapping is mainly used for trees whose root ball needs to remain intact above ground for some time, such as conifers that stand at a garden centre for a period before being sold. These jute-acrylic mesh cloths will not decompose and must be removed, otherwise the soil will become polluted. Very small trees are also sometimes fitted with root ball elastics. These are recognisable white elastics placed crosswise around the root ball. These too must be removed during planting to prevent pollution.

Towards the end of the lifting season, around March / April, we also come across root balls wrapped in coconut fibre. This material is often used for trees that are delivered well after the lifting season. Coconut fibre decomposes more slowly than jute and makes it possible for trees to remain on the container field for a season on drip irrigation. The coconut root ball wrap can retain some moisture and therefore helps to prevent drying out. It may happen that a landscaping project is delayed, and that the use of coconut fibre around the root ball still ensures a perfectly manageable root ball by the time the trees are eventually delivered. This coconut fibre can remain in place during planting; like jute, it will eventually decompose completely. In short, the advantage of coconut fibre is that it extends the planting season until June; if planting is to take place even later, we recommend the use of the Air-Pot®.

Once a tree has been planted, the crown should be pruned back to restore the balance between root volume and crown volume and to limit transpiration. Trees always lose roots during lifting and transplanting. If no pruning is carried out, there is a risk that the crown will become too large for the limited number of roots and that the tree will not be able to supply enough water for transpiration; this imbalance can lead to dieback of branches or worse. This risk occurs particularly with fast-growing species and in coastal areas.

When planting, we advise pruning back the crown by no more than 25%. The pruning should be aimed more at reducing the size of the crown (pruning on the outer edge of the crown) than at thinning the crown. If branches have been broken or damaged during transport, thinning is necessary or pruning back to a side shoot.

Branches that have been pruned start to grow much faster and are much more resistant to diseases and insects. By the end of the first growing season, they will have returned to the shape of the crown before pruning. During the second growing season, they will become broader than trees that were not pruned. After planting and the first pruning, it is not necessary to prune the trees for the next three years.

Many trees have their most favourable growing conditions in woodland. Forest soil contains a large amount of humus, nutrients and a complex variety of soil life, including many micro-organisms such as fungi. Soil improvement with fungus-dominated humus compost approximates the ideal growing conditions for trees as closely as possible and enriches biological soil activity, which ultimately ensures that nutrients become available to the tree. Humus compost can be mixed with poor topsoil at up to ten per cent to form a good growing medium. The remainder of the humus is useful for enriching the top layer (top 20 cm) of the planting bed so that it can be incorporated into the soil by the worms present, helping to maintain oxygen levels and increase the soil’s moisture-buffering capacity.

After preparing the planting hole and carrying out any necessary soil improvement, the trees can be planted. The trunk of the tree is wrapped in jute, after which the tree can be lifted either with a sling around the root ball and trunk or with a root ball hook. The tree is placed in the planting hole with the top of the root ball about five to ten centimetres above ground level. This is because the soil in the planting hole will still settle, especially with heavy trees. The tree settles with it and will eventually stand lower than the planting height. It is better to plant the tree too high than too low. Trees planted too low have a high risk of oxygen deficiency, with associated root rot and dieback. Since the roots of a tree grow to just below the soil surface, planting too high is also not desirable. Trees planted too high dry out easily, because the roots will eventually protrude above ground level. Adding soil to cover the roots in the form of a mound can also lead to drying out, because the water runs off the mound during watering.

“It is better to plant the tree too high than too low. Trees planted too low have a high risk of oxygen deficiency, with associated root rot and dieback.”

When the tree is standing in the planting hole, aeration must first be installed, particularly in paved soils and soils with a high organic content, such as peat soils. This aeration is needed to supply oxygen to the roots. Once the aeration has been installed, the planting hole can be filled.

First, the planting hole is filled to one third and firmed down. Take care that no organic materials such as turf enter the planting hole, as these materials deplete oxygen.

Secondly, the planting hole is then filled to three quarters, and the wire around the top of the root ball must be loosened. If a wire lies tightly against the trunk, there is a risk that the tree will be constricted at that point as it grows in girth.

Lastly, the planting hole can then be completely filled and firmed down once again. Never remove the wire from the top of the root ball before the tree is placed in the planting hole, as there is a high risk of the roots breaking.

Despite all careful handling, a tree can still be damaged during planting. Especially towards the end of the delivery season, in early spring, the sap flow in many species has already started and they are extra sensitive to damage. As long as it concerns minor damage (max. 10 to 20% of the bark circumference), this can be treated well with tree wound balm (brand name Lac Balsam), available from suppliers in the green sector. If the trees are delivered by our own lorry, our driver sometimes has it with him and may be able to offer a helping hand. If the damage is no greater than 30% of the bark circumference, the tree may eventually grow over it. The speed of this process depends on the species, and not all species close wounds well without leaving a visible scar. The greater the damage, the more effort (and energy) it will cost the tree to recover. Where possible, it is advisable to turn the wound out of sight so that it is less noticeable when the planted space is used. It can also help to turn the damaged side to the north, so that the wound grows over more easily because of the shade and cooler conditions. Whether the tree will eventually grow over the wound completely depends on tree-biological factors (and, in the case of pruning, also on correct pruning practice). This recovery must come from the cambium (wound tissue), which grows over the wound from the remaining bark tissue. The tree therefore needs time to recover a wound. If the tree has been completely girdled during unloading, and the bark has been entirely stripped away, it will not survive. In that case, the advice is to reorder the tree from the nursery as soon as possible to avoid delays in carrying out the project.

The size of the lifted root ball depends on a number of factors. The most important factor is the trunk circumference of the tree and the volume of the crown. In addition, the shape of the tree also has an influence; for example, an avenue tree is given a different root ball size when lifted than a multi-stemmed tree. The tree species also has some influence: some species can be lifted with a smaller size, while others require a relatively larger root ball. When preparing for planting, it is important to know what size the planting hole should be, so that the tree can be placed in the planting hole as quickly as possible after or during unloading. Please consult the Root Ball Information Table for the dimensions. In addition to the diameter, this table also gives a good indication of the height and weight of the root ball. Because different lifting machines and different soil types are used, there will always be some variation. If the exact dimensions and weight are particularly crucial, please consult your contact person about the available options before ordering.

Drive the stakes firmly into the ground, if necessary with the aid of an auger. It is preferable to drive the stake twenty centimetres into the firm ground beneath the planting hole. As a general rule, at least one third and no more than half of the stake should be buried. Secure the tree to the stake or stakes with tree ties. Let the tie cross itself between the tree and the stake to prevent friction and, with it, damage to the trunk. Check the ties and stakes at least once a year so that the ties can be adjusted in good time if constriction occurs. When a tree with a bare root system is planted, the stakes should be positioned before planting to prevent damage to the roots. It is advisable to check the tension of the tree ties a few weeks after planting, as settling of the tree due to soil cultivation may reduce the tension. If the soil allows, the tree stakes can also be pushed into the ground using the bucket of an excavator, after which the trees can be planted.

Above-ground anchoring is used most often and is the cheapest and quickest way to secure a tree when planting. In most cases, this consists of anchoring with two or more tree stakes braced with tree ties. This anchoring remains in place for around two to three years, until the tree has rooted sufficiently to support itself. After that, the stakes are removed in phases. If only one tree stake is used, it must be placed on the side of the prevailing wind direction. The tree will then ‘blow’ in the opposite direction to the stake. If this is not done, the tree will strike the stake too often, causing damage through which parasites can enter the tree. In the case of swirling or downdraught winds around tall buildings, or with larger trees, several stakes are required. If two or more stakes are installed, the advantage is that a so-called watering rim can be attached to them, helping it to stay in place more effectively. Do note that the tree ties should not be fixed too rigidly; a certain amount of play encourages rooting and, ultimately, quicker establishment. It is also important to check the tension of the anchoring a few weeks after planting. The soil often settles somewhat after planting, which affects the anchoring and the tension of the tree ties.

Underground tree anchoring, also known as root ball anchoring, provides stable and reliable anchorage for trees that remains invisible after installation, unlike the more common above-ground anchoring. It is a slightly more labour-intensive method during installation, but a highly effective solution. The anchoring can be achieved by placing tension straps or a seatbelt strap over the root ball and securing these to underground stakes or horizontal steel anchors. The tree tie is then properly tensioned using a ratchet. The advantage of underground anchoring is that there is no visually intrusive support, the bark cannot be damaged by rubbing tree ties, and the tree roots are free to develop evenly without interference from stakes. With this method too, it is important to check the tension of the anchoring a few weeks after planting. The tree may settle slightly after planting, which can reduce the tension on the anchoring. When anchoring a large-sized tree, crown anchoring will also need to be applied. Please consult your contact person for this.

When planting large trees, proper anchoring is essential to ensure stability during the first few years. In addition to traditional tree stakes, crown anchoring with guying is also often used. Crown anchoring consists of cables installed in the crown, usually between the main stems or heavy branches, which keeps the tree stable in strong winds. It is important that the materials used cannot rub or become embedded and cause damage. After three years, the system must be removed to prevent ingrowth.

The major advantage of crown anchoring during planting is that the tree can develop more freely. The roots are given the opportunity to establish themselves naturally, while the crown is still sufficiently protected against wind loading. Installing crown anchoring requires expertise: the straps must be fitted at the correct height, without damaging the bark, and must retain enough flexibility to allow the tree to move naturally. After a few years, once the tree has established well and is standing firmly, the anchoring must be removed. In this way, crown anchoring contributes to successful planting.

A number of tree species are becoming increasingly sensitive to bark scorch. This mainly occurs on the side where the late afternoon sun shines on the bark. It arises because the tree already has a moisture deficit during the day, the sap flow slows down considerably, and the bark then heats up intensely in the strong evening sun. For species with thin, smooth bark growing in a sunny position, trunk protection is usually necessary during the first three years after planting. Acer (maple), Castanea sativa (sweet chestnut), Cercidiphyllum japonicum (katsura tree), Fagus (beech), Liriodendron (tulip tree), Tilia (lime) / (linden), Carpinus (hornbeam) and Magnolia are particularly susceptible to bark scorch, which can cause the bark to detach from the trunk. This can be prevented by protecting the branch-free part of the trunk after planting with jute, reed mats, coconut mats or by applying Arboflex. After a few years, these materials will have decomposed and the tree will have built up resistance to sun scorch. By then, the crown will also have increased in width, so that the trunk will be more shaded. Painting the bark with a white lime-based paint can also be an effective solution. Would you like to know more about protecting the tree trunk against bark scorch? Read the article: Trees need protection against sunburn too. 

For the tree stakes, a choice can be made between treated wood (painted, impregnated or tarred) and untreated wood from species that do not rot quickly, such as Castanea sativa (sweet chestnut) or Robinia hispida (bristly locust). Treated wood contains harmful substances that remain in the soil and can be absorbed by the tree roots. This is not beneficial for either the environment or the tree. It is therefore advisable to choose untreated wood. Preferably use short above-ground tree stakes that protrude no more than eighty to one hundred centimetres above ground level. When short tree stakes are used, trees have more freedom of movement and therefore develop stability roots more quickly. The tree will then anchor itself sooner and more effectively. Longer tree stakes, by contrast, make the tree static and ‘lazy’, resulting in poorer anchorage in the short term. In addition, long stakes have a negative effect on the thickening growth of the trunk. Below the tie point, the trunk increases in thickness less quickly than above the tie point, because part of the bending stress is absorbed by the stake.