The watering of large planted / transplanted trees, especially during the summer months, is critical to the survival of trees and speedy establishment of new roots. Lack of, or incorrect / ineffective application of water can lead to the death of trees within a period as short as 7 days during conditions of extreme heat and wind.

These newly planted / transplanted large trees should be regarded as trees that are growing in small containers / pots without side walls positioned in the ground. Water applied at the top of the container, can freely drain away in the surrounding (less dense and more permeable) soil, at the cost of penetration and saturation of the “container” soil (root ball).

Successful watering is only achieved when the root ball is being saturated with water. Achieving this is easier said than done. It is also difficult to measure and check effectiveness with the root ball being underground. The main problem in achieving complete root ball water penetration is, in most cases due to the fact that the surrounding backfill soil is less dense and more permeable than the root ball ( where all the tree roots occur).

In the case of the tree being planted in a heavy clay soil, a serious danger of over watering and the resultant fatal drowning of the tree can occur. In this case the walls of the clay planting hole create an almost water tight container (without drainage holes at the bottom of the “clay pot”). This planting situation makes it very tricky to achieve successful watering whilst avoiding over watering. In these situations, it is most desirable (almost essential) to have a water drainage outlet installed as low down in the planting hole as possible.

How to achieve effective watering of the root ball post planting:

• Slow low volume watering over long periods of time
• Apply water as close to the stem (inner one third of root ball surface) as possible. Apply on 2 to 3 sides of the stem, simultaneously or by moving the water supply from the one to the next side around the tree.

The above procedure will ensure that the water will first gravitate downwards, and once saturated, water will start to radiate laterally through the root ball to areas of lower water saturation, until excess water finally drains away at a faster rate in the surrounding back fill soil. If you have no other option than to water in a shorter than desired period of time, a dam wall must be constructed on top of the outer border of the root ball (not beyond the root ball perimeter).

Volume and of water required:

• 5 to 8 % of the root ball volume. In the case of a 1.1 meter diameter ball (+- 1000liter bag / ball) that will be 50 to 80 litre and in the case of 1.8 meter diameter ball (2500 litre) that will be 130 to 200litre of water. BEWARE OF TO MUCH WATER IN HEAVY CLAY SOILS.
• In the case of the surrounding soil having very good drainage (e.g.sand and alluvial rock substrates) you can safely water up to 10% thereby reducing the probability of under watering without risking the drowning of the tree.

Frequency of watering:

• During periods of high water demand (summer), the tree depletes the relatively small volumes of water available in the root ball or “container “ volume in a short period of time (within 3 to 5 days). It is for this reason that the frequency of watering is just as critical to tree survival during the early stages following planting.
• Frequency depends on one or more of the following: season, species (water requirements and whether deciduous or evergreen), soil type, foliage density, and time elapsed since planting (volume of new roots established).
• General guide lines for frequency of watering:

YEAR TWO AND THREE following planting:
For optimal tree recovery, growth rate and health continue to water as recommended for the first year following planting. Increase watering volume to 2 times the volume prescribed for year one. The trees will, in terms of tree survival, become less sensitive to the skipping of watering sessions but are still very dependant on regular artificial watering during the summer months in the winter rainfall areas.

YEAR FOUR AND FIVE FOLLOWING PLANTING:
For optimal tree growth rate and health continue to water at half the frequency (every second time) recommended for the first year following planting. Increase watering volume to 2 to 3 times the volume prescribed for year one. During the hot and windy periods in the summer, trees do still require deep watering once every 3 weeks and more regularly in sandy soils.

MORE THAN 5 YEARS AFTER PLANTING
Deep water all established trees under the drip line of the tree canopy once a month during hot and dry summer months.