When is the best time to plant rootballed trees?

The best time to plant rootballed trees is, as a rule, the dormant period. At Diaplant, the main planting season runs from November to April.

During these months, many deciduous trees are leafless and the crown loses far less water. Lifting and transport become safer, and the tree can begin to recover its roots before facing the summer heat.

The window should not be used as an automatic calendar. A tree still active in November, a saturated soil or a very early spring may mean the operation has to be postponed or cut short.

When a tree is lifted, only part of its roots come with the rootball. Its capacity for uptake falls immediately.

In a leafless deciduous tree, transpiration is far lower. The roots that remain have less leaf area to supply while they begin to recover and explore the new soil.

Dormancy also makes it easier to tie in the crown for transport. The branches of many species become more flexible and are not carrying the weight of foliage.

That does not mean the tree is completely inactive. Roots can stay active, or resume activity, when soil temperature and moisture are suitable.

Some trees go dormant early. Others hold their leaves until late autumn, especially in mild years.

The team looks at the actual state of the plant before lifting. The calendar saying November is not enough if the crown is still active and conditions are not favourable.

The same care applies at the end of the season. A species that breaks bud in March runs out of margin sooner than one that stays dormant until April.

The location of the destination counts too. A tree may leave a colder nursery for a coastal site where spring is already under way.

Evergreens keep their leaves through the winter and go on transpiring. They benefit from the lower temperatures, but do not have the same drop in demand as a leafless deciduous tree.

Rootball moisture, protection during transport and watering after planting are particularly important.

Some evergreen species are sensitive to cold on recently disturbed roots. The choice of timing should balance the risk of heat against the risk of low temperatures.

The soil needs to allow a clean lift and a rootball that holds together.

When it is too dry, it can lose structure and crumble. When it is saturated, it deforms and gets heavier, and passing machinery compacts the fields.

The operation may be postponed even within the right season. Preserving the quality of the rootball matters more than meeting a delivery date when conditions are wrong.

The planting hole and the surrounding area also need to be in fit condition.

Planting into saturated ground destroys structure and leaves the roots without oxygen. In frozen or very dry soil, contact between rootball and ground is compromised.

Drainage should have been assessed before the tree arrives. A tree should not be left unloaded on site waiting for an improvised solution.

Rain can wet the surface and leave the rootball dry. Differences in texture between the rootball and the surrounding soil change the way water gets in.

After planting, a deep watering is given to settle the ground and confirm that water reaches the whole root mass.

In spells without rain, moisture continues to be checked. The need rises as spring advances and the crown becomes active again.

A container gives more flexibility because the roots are not cut when the tree leaves the nursery. Even so, planting in intense heat increases the watering required and the likelihood of stress.

A plant that has been in its pot too long may have deformed roots, whatever the season.

The production system should be assessed together with the climate and the capacity for aftercare.

Building works, events or access restrictions can create pressure to plant at another time. For field-grown mature trees, that decision should be exceptional and technically assessed.

You need to know the species, the stage of growth, the root volume, the transport distance, the availability of water and whether daily aftercare is possible.

In some cases, it is better to hold the tree at the nursery, change the programme or select suitable container-grown stock. Flexibility on site should not be bought at the expense of the specimen’s viability.

Large trees need to go in before walls, paving or structures close off the access. This dependency should be considered from the outset.

The programme cannot put planting at the very end simply because it is a visual finish. In many projects, it is a heavy operation that shapes the construction sequence.

The best time is where dormancy, soil conditions and logistical availability meet. When these three conditions line up, the tree begins its establishment at lower risk.

• Planting mature trees
• How a tree is prepared before dispatch
• How to water a mature tree in its first year

1. European Arboricultural Standards. European Tree Planting Standard.
2. Allen, K. S. et al. (2017). Review of production systems and the survival of urban trees.
3. Diaplant’s method for dispatch and planting.