What a tree’s rootball is and why it matters

The rootball is the volume of soil and roots that goes with a tree when it is lifted from the field. In a mature tree, it is not just earth clinging to the roots. It is the part of the root system that has been prepared for transport and that will have to sustain the tree while it adapts to its new site.

The quality of the rootball depends on earlier transplanting, the distribution of the roots, the cohesion of the soil, moisture and the way lifting is carried out. It also determines the weight of the tree, the choice of machine, the transport, the size of the planting area and the equipment needed on site.

When a tree grows in the field, its roots extend beyond the zone that can be transported. That is why mature trees are transplanted within the nursery during the production cycle.

Each transplanting cuts part of the roots that have grown away from the trunk. Once replanted, the tree forms new roots closer to the cut. Over time, the amount of root increases within the area that may come to form the rootball.

At Diaplant, trees in the mature range are transplanted at least twice. By the time of final lifting, root preparation has already been under way for several years.

The rootball is formed on that day, but its quality comes mainly from the earlier work.

A rootball has to keep soil and roots together during lifting, loading, transport and planting.

Cohesion depends partly on the type of soil. Soils with some clay fraction tend to hold their shape more easily; very sandy soils may call for more care because they fall apart more readily. Moisture also influences behaviour. A soil that is too dry loses cohesion; when saturated, it can deform and add even more to the weight.

The roots help to bind the mass of soil. A well-rooted rootball stays more stable than a volume with little root distributed through it.

There is not, however, a single appearance for all specimens. The form and density of the roots vary between species, ages and production cycles. The assessment has to consider the actual tree.

The size of the rootball must be compatible with the size of the tree and with the amount of root that needs to go with the specimen.

The girth of the trunk is an important reference, but on its own it cannot define a universal measurement. The species, the architecture of the root system, the soil and the transplanting history also count. Two trees with the same girth may need different rootballs.

Logistics bring further limits. As the diameter increases, volume and weight grow quickly. A small increase in the measurement can change the machine needed, the crane capacity, the type of transport and the conditions of access to the site.

For that reason, the dimensions are defined case by case and coordinated with the planting. It makes no sense to select a tree and only then discover that the rootball cannot reach the intended site.

For most trees, lifting is done with a specialised rootballing machine. The blade cuts the soil and the roots around the specimen and forms a volume with controlled geometry.

The blade size is chosen according to the size of the tree and the needs of the species. With very large trees, especially when the rootball exceeds about 120 cm in diameter, it may be necessary to bring in an excavator and more work by hand.

After the cut, the team firms and trims the rootball so that it stays as a single unit. The operation has to preserve the roots and avoid cracks that could open up in transit.

The specimen is then wrapped in hessian and wire mesh. These materials hold the soil together and allow the tree to be handled without putting direct pressure on the trunk or on exposed roots.

Diaplant uses materials from suppliers who specialise in the sector, with biodegradability certification for both the hessian and the wire mesh.

The team forms, firms and wraps the rootball so that the materials stay in place during planting. We do not recommend removing or loosening the mesh on rootballs prepared by our method.

Taking the wrapping apart can lose the cohesion achieved in the field. The soil can open up, the roots can be left unprotected and, in extreme cases, the rootball can break up enough to compromise the viability of the tree.

This procedure refers to rootballs prepared by Diaplant and to the materials we use. It should not be applied automatically to trees from other suppliers without knowing how they were produced, the type of mesh and the specification of the material.

When a specification requires a different method, the matter should be reconciled before dispatch and not decided only at the moment of planting.

A rootballed tree should be handled by the rootball itself or by the lifting points prepared for the operation. The trunk must not bear the weight of the specimen.

With large trees, the combined weight of the soil, roots, trunk and crown can be very high. The team defines in advance the lifting equipment, how the tree is secured on the vehicle and the order of unloading.

The rootball must be kept protected from drying out and from knocks. A crack that looks small during loading can grow with the vibration of transport. It is also important to limit the time between dispatch and planting.

The crown and the trunk are given their own protection, but neither should be used to make up for inadequate lifting of the rootball.

The first point is to confirm that the rootball has held together and that the wrapping shows no significant breaks.

Moisture should be checked, especially in dry weather or after a long journey. The root collar of the tree also needs to be located. The top surface of the rootball does not always correspond to the correct planting level, because soil may have built up against the trunk.

The size should match what was planned for the planting hole, the crane and the anchoring system. With a mature tree, improvising at this stage can cause damage or lead to planting too deep.

The rootball carries the roots the tree has available at the moment of planting. It does not replace the soil in which those roots will have to grow.

If the surrounding ground is compacted, water can be held at the surface and fail to reach the inside of the rootball. It can also collect around the tree without draining, reducing the oxygen available. In both cases, the roots struggle to grow out into the new soil.

Preparation of the planting area should therefore consider the ground and not just the size of the rootball. At Diaplant, we recommend as a basic rule an opening prepared to a width and depth of at least twice its size. In compacted or little-cultivated soils, the greater the volume that is loosened, the better the conditions for establishment.

For a large tree of medium maturity, a general guide is to prepare about 8 m³, equivalent to 2 × 2 × 2 m, where the site and the species allow. This figure represents a volume of prepared soil, not the depth at which the tree should sit. As a rule, the root collar stays level with the finished ground or slightly above it, depending on the soil and the species.

After backfilling, a deep, soaking watering is needed. The water should pass through the rootball and wet the surrounding soil.

This first watering helps to reduce air pockets, settle the soil and improve contact between the roots, the rootball and the prepared ground. It should not cause excessive compaction or leave the tree permanently saturated.

In the days that follow, it is useful to confirm how the moisture is distributed. A simple way is to open small inspection holes of about 20 cm beside the rootball, to see how far the water is reaching and how the ground is draining.

The aim is not to keep the surface constantly wet. Deep waterings are preferable, with sufficient volumes and intervals adjusted to the climate, the soil and the species.

Preparation in the nursery gives the tree a more favourable root base, but the work on site remains decisive.

An intact rootball can fail in a soil without drainage, with shallow watering or with the root collar buried. Equally, a well-planted tree will struggle more if the rootball has dried out, lost cohesion or been damaged during unloading.

Selection, transport, soil, planting and aftercare are part of the same process. The rootball is what makes it possible to take the roots from the nursery to the new site, but adaptation depends on what happens afterwards.

The size of the rootball, the transport and the planting equipment should be assessed together with the specimen and the site conditions.

Talk to Diaplant about a mature tree Get to know the nursery

• How a mature tree is formed
• Why we transplant trees within the nursery
• Planting mature trees: from rootball to adaptation
• Size of the planting hole

1. European Arboricultural Standards. European Tree Planting Standard, 2025 revision.
2. Watson, G. W.; Sydnor, T. D. (1987). “The Effect of Root Pruning on the Root System of Nursery Trees”. Journal of Arboriculture, 13(5), 126–130. DOI: 10.48044/jauf.1987.027.
3. Gilman, E. F.; Paz, M.; Harchick, C. (2016). “Effect of Liner Container Size, Root Ball Slicing, and Season of Root Pruning in a Field Nursery on Quercus virginiana Growth and Anchorage After Transplanting”. Arboriculture & Urban Forestry, 42(4), 234–245. DOI: 10.48044/jauf.2016.022.