Watering Newly Planted Trees - Part 1

By far the most critical aspect of tree establishment is the correct application of water.

When a new tree is planted, the only place it has roots is in the rootball.  We therefore need to keep that rootball moist, until such time as the tree has grown new roots out into the surrounding site soils, far enough for it to be able to function on soil moisture levels, rather than rootball moisture levels.

The water applied to new Urban Trees needs to be placed carefully.  During the initial establishment period all water must be directed to the rootball: the only place where roots are to be found.  This can be done using drip irrigation, where the drippers are concentrated on top of the rootball, or by containing the water applied manually so that it must pass into the rootball and not run off (e.g. Using well-maintained watering rings).

Note: It is essential that the amount or water applied relates to the size of the tree/rootball, at the time of planting. 

However, as the new roots develop, water must be applied in such a way that it “encourages” new root development out into the surrounding site soils.  Once the new roots have begun to occupy the surrounding site soils, the frequency of water application needs to be reduced, but the amount of water applied, per application, increased.  This allows for the water applied to “wet-up” site soils surrounding the rootball, and for the rootball itself to dry out a bit, between waterings, encouraging roots to grow outwards.

See Field Guide for Watering Newly Planted Trees for suggested application rates and frequency.

It is important to remember that the surface area of the root system of a newly planted tree is very small.  That means that the amount of water that falls onto the top of the rootball, during a rainfall event, is minimal.  Don’t think that because it has rained that the tree has been watered adequately: keep watering. Similarly, irrigation designed for grass, or garden beds, is unlikely to provide enough water for the newly planted tree: additional water will need to be applied, directly to the rootball, in the short to medium-term.

See New Plantings – Early Watering Requirements and the Impact of Rain.

Where mulch is to be applied to newly planted trees, it is important that it is relatively thin (say less than 40mm thick) and kept off the top of the rootball (e.g. only mulch outside the watering ring), so that it does not inhibit water penetration.

Just like tree stock quality, and correct planting techniques, high-quality establishment and maintenance practices, particularly watering during establishment, are critical to the success of the newly planted tree.  Establishment can take several months for smaller sizes, and up to 2-3 years for bigger trees.  However, to short-change this work is to risk both squandering the opportunity the new planting represents, and wasting all the time, effort, and money, expended.