• Excessive watering: an introduction
• Symptoms of overwatering
• Ensure an optimal planting site
• Dealing with wet locations
• Choosing the right tree species​

Weather extremes are making tree planting increasingly demanding. After dry years have come extremely wet years, with high groundwater levels causing waterlogging even on sandy soils. Overwatering caused by precipitation not only from rain, but sometimes also from excessive irrigation, leads to root rot, oxygen deficiency and reduced stability. Without oxygen in the soil, root growth is hindered and diseases increase. Good drainage, tailored to the soil type and climate, is crucial for healthy trees. A balance between moisture, oxygen, light, nutrients and soil life is essential. Excessive watering not only affects young planting; established trees can also suffer serious damage. We are happy to help you recognise the symptoms of overwatering more easily.

The first symptom of too much water is discolouration of the leaves, which become dull. The follow-up symptoms all closely resemble drought stress, simply because with root rot the tree can no longer take up moisture and therefore effectively dries out. In cases of drought, we see the damage starting in the outermost parts of the crown and moving inwards, whereas in an excessively wet situation this pattern is exactly the reverse. There, the damage spreads from the centre of the crown outwards, while the tips of the branches often remain fresh green.

Deciduous trees on a site that is too wet often show the following symptoms:

Wilted leaves: despite sufficient moisture, the leaves may still begin to droop. The cause is a lack of oxygen at the roots and possibly even root rot, making moisture uptake impossible. This leads to wilting of the leaves.
Leaf discolouration: the tree shows brown leaf margins and yellowing. Overwatering can lead to nutrient deficiency, mainly because essential nutrients are washed away from the roots.
Premature leaf fall and dieback: an important sign of decline is the dieback of young shoots, including the leaves. However, this can also be a sign of too much water. In both overwatering and underwatering, these are signs of a stress response by the tree.
Root rot: nearly all these symptoms are caused by poor condition of the root zone, resulting in root rot. By carefully digging away the soil around the roots, they become exposed; black roots are a sign that they have been affected by root rot. Fungi (such as honey fungus) are also often visible, having a negative effect on the roots and thriving under oxygen-poor conditions. Root rot can also be recognised by a musty smell, sometimes with the characteristic odour of rotten eggs.
Other diseases: diseases such as Phytophthora and Verticillium also frequently occur in cases of excessive watering. The first is a water mould and a precursor to root rot. The second is a wilt disease that blocks the xylem vessels and causes wilting.

In many places where trees are not surviving this wet year, the cause lies in the planting site conditions. This may be because work was still carried out in wet conditions, which has ruined the soil structure. It may also be because the tree was planted too deeply in relation to the ground level and/or the groundwater level. Because of the completely wet planting site and the lack of oxygen, the tree fails to root out from its root ball and produces too few or no fine roots, which are crucial for the uptake of water and nutrients. A root ball consisting of a different soil composition from the surrounding soil may also dry out because it does not take up water. Wet locations are often very localised, so the moisture content of the root ball should always be assessed separately from that of the surrounding soil.

The simplest way to take wet conditions into account is to plant the trees on a small mound: make sure that the bottom of the root ball is always planted above the highest groundwater level. This ensures that water always drains away from the root ball and that the roots always receive sufficient oxygen when the groundwater level is high.