Trees in drought stress

Table of Contents

• Drought stress in trees: The most important points at a glance
• What is drought stress?
• Causes of drought stress in trees
• Which trees are particularly susceptible?
• Recognizing drought stress: The most important signs
• Recognizing drought stress and differentiating it from diseases
• When does drought stress become dangerous for trees?
• What to do against drought stress?
• Preventing drought stress: How to protect your trees in the long term
• Summary: Drought stress in trees

When did you first hear about drought stress in trees? For me, it was in the fall of 2020. And since then, I've been hearing the term "drought stress" again and again, and with increasing frequency. Perhaps drought stress has now become the new normal. At least since 2018, it seems that trees have hardly experienced a summer that didn't challenge them with heat and drought. It's time to take a closer look at the topic of drought stress in trees.

Drought stress in trees: The most important points at a glance

• Drought stress develops due to persistent water shortage
• First signs are drooping or discolored leaves
• Particularly at risk are young and urban trees
• Main measure: proper and sufficient watering
• 150-200 liter Each watering process helps effectively

What is drought stress?

Drought stress is a condition caused by a lack of water. Water is a vital elixir for trees, required for almost all biochemical reactions. Without water, they become diseased or die. For example, trees suffering from water shortages can no longer effectively defend themselves against pests such as fungi or bark beetles. Drought stress therefore makes trees susceptible to disease. 

If the trees lack water, the first reaction is to close their stomata, the small stomata, and thus no longer be able to carry out photosynthesis. If they did not close them, more water would evaporate from these small openings and the tree could dry out. However, without the sugar produced by photosynthesis, the trees lack the building material for growth, fruit and seeds.

If this immediate measure does not help enough, trees have other strategies. Some tree species can reduce solar radiation by drooping or curling their leaves. Other tree species start moving their leaves, such as the aspen. With even more severe water shortages, some trees will also begin to shed leaves. And some trees, such as oaks, poplars and willows, also shed whole branches.

If the lack of water lasts for a longer period of time, entire parts of the tree can eventually die. The tree prefers to sacrifice some parts in order to be able to continue living. If the tree can no longer save itself through this, it will dry out.

Causes of drought stress in trees

Drought stress is not solely caused by a lack of rain. In many cases, several factors combine to prevent trees from receiving sufficient water:

• In addition to prolonged periods of heat, soil composition also plays a role: compacted soils, such as those often found in cities or heavily used gardens, are less able to absorb water. The water runs off the surface instead of reaching the root zone.
• Sealed surfaces also play a significant role. Asphalt, paving stones, and concrete prevent rainwater from seeping into the ground. This makes urban trees particularly vulnerable to drought stress.
• Another factor is the tree species itself. Some species cope better with drought, while others are significantly more sensitive. It becomes particularly problematic when trees are planted in regions that do not correspond to their natural habitat.

Which trees are particularly susceptible?

In principle, all trees can suffer from drought stress in the hot summer months, including trees in forests. In most cases, however, trees in towns and villages as well as on orchards are much more affected by drought stress. In forests, trees cool each other's air, and the forest floor is covered with organic matter, making it much more sheltered than urban soil. In cities, on the other hand, there are higher average temperatures, additional pollution and compacted soils. The more urban a tree's environment is, the more susceptible it is to drought stress.

Another important factor is the type of tree, because each has its own climatic comfort zone. Some tree species cope better with drought stress than others. Here you can find an article about City trees of the future.

Young trees are particularly susceptible to drought stress. Their roots are not yet strong enough to penetrate the deeper soil layers to draw water. Young trees in particular should be watered in dry and hot weather.

Recognizing drought stress: The most important signs

Here are the most important signs of drought stress in trees:

• Dried, drooping, curled, or folded leaves
• leaf wagging or trembling
• shedding of leaves
• shedding of branches
• Formation of significantly smaller leaves
• Formation of excessively many and small fruits
• When trees are watered, there is often an immediate recovery

If a dry period lasts up to four weeks, most trees can still handle it reasonably well. A dry period of two to three months, on the other hand, is already critical for many trees. The more often dry periods occur in a growing season, the more difficult it becomes for the trees. They then lack the time in which they can regenerate.

Recognizing drought stress and differentiating it from diseases

Not every change in a tree is automatically a sign of drought stress. Therefore, it is important to correctly interpret typical symptoms:

• Drought stress is often indicated by drooping, curled, or dry leaves. These often appear limp and lose their elasticity. Premature leaf drop can also occur, especially during hot summer months.
• In contrast, many diseases manifest themselves through spots, discoloration, or localized damage to the leaves. Fungal infections often appear as clearly defined patterns or coatings on the leaf surface.
• Another distinguishing feature is the timing. If the symptoms appear during prolonged dry periods, the cause is usually a lack of water. If they occur regardless of weather conditions, a disease or pest infestation could also be the cause.
• If in doubt, it's worth checking the soil. If it's dry, drought stress is very likely the cause. If the tree's condition improves after thorough watering, drought stress was probably the cause.

When does drought stress become dangerous for trees?

Not every dry spell is automatically critical for a tree. However, if a dry period lasts for several weeks, the trees become increasingly stressed. After about two to four weeks without sufficient water, the first signs of reduced growth and vitality appear.

If the water shortage is not remedied over several months, permanent damage can occur. The tree loses leaves, its growth is reduced, and it begins to shed parts of its crown.

It becomes particularly problematic when several dry periods recur within a single year. In this case, the tree lacks the time to regenerate, which significantly weakens its resilience in the long term.

What to do against drought stress?

The most important and efficient means of combating drought stress is tree-friendly wateringKISSINGThe most important rules are:

• A lot of water at once, but not too often.
• During periods of drought and heat, trees should be watered 2-3 times a week with 150-200 liters of water each time.
• It is also important that the water is not released too quickly. If water is released too quickly, a large portion of it runs off the surface without being able to seep into the deeper root zones.

For example, the following are suitable: tree bath tree watering bagsThe bags are placed around the trunk, sealed, and then filled with 75 to 100 liters of water, depending on their size. The water is released drop by drop into the soil through small holes in the bottom over a period of 6 to 9 hours. Drip irrigation the soil in the root area of ​​the tree has enough time to absorb and store the water. Multiple bags can also be connected together, allowing 150 liters of water to be dispensed in one go.In addition to tree-friendly watering, you can also care for the root area of ​​the tree in such a way that it can absorb and store the water well. The following measures can help:

• Plant accompanying greenery: Other plants in the root area root through the soil and ensure that the water can seep away better.
• Mulching: A mulch layer This ensures that the soil can retain moisture better and stay soft for longer. Soft soil can absorb and retain water more effectively.

Preventing drought stress: How to protect your trees in the long term

The most effective approach is to prevent drought stress from occurring in the first place. With proper care, you can stabilize your tree in the long term:

• Regular and appropriate watering during dry periods plays a crucial role. If trees receive sufficient water early on, they won't even reach a critical condition.
• Soil care is also crucial: Loose, humus-rich soil can absorb and retain water much more effectively. Measures such as mulching or incorporating compost sustainably improve soil structure.
• Organic soil improvers are particularly effective for this, such as... Worm compostThey promote soil life, increase humus content, and ensure that water remains available in the root zone for longer. Baumbad liquid fertilizer It is based on high-quality worm compost and is particularly well suited to specifically support these effects and improve the soil's water retention capacity in the long term.
• Furthermore, appropriate planting in the root zone can be helpful. Companion plants promote root penetration into the soil and improve its ability to retain water.
• In this article you will learn more about the system of water, nutrients and soil for trees.

In the long term, it is also worthwhile to pay attention to suitable tree species when planting new trees, as these are better adapted to the respective site conditions.

Summary: Drought stress in trees

Trees suffering from drought stress show various signs and can develop significant health problems. Drought stress occurs when trees do not receive sufficient water to meet their physiological needs. Here are some signs and effects of drought stress in trees:

1. Leaf discoloration and fall: An early sign of drought stress is leaf discoloration. They may turn yellow, develop brownish edges, or fall off prematurely.
2. Wilting and drying out: Trees under drought stress often show signs of wilting, particularly of leaves, needles or twigs. The leaves can dry out and lose their elasticity.
3. Reduced growth: Drought stress can affect the growth of trees. The formation of new shoots and leaves may be reduced, and the overall development of the tree may be inhibited.
4. Cracked bark: If drought stress lasts for a long time, the bark of the trees can develop cracks. This happens because the tree removes water from cells to maintain vital functions.
5. Lower fruit production: Trees may produce fewer fruits under drought stress because water is necessary for flower and fruit formation.
6. Susceptibility to diseases and pests: Drought stress makes trees more susceptible to diseases and pests. Weakened trees often have difficulty resisting pathogens and insect attacks.
7. Reduced photosynthesis: Drought stress affects the ability of trees to photosynthesize. This process by which plants convert light energy into chemical energy is essential for their growth and energy production.
8. Changes in metabolism: Under drought stress, trees can adapt their metabolism to conserve water. This can lead to changes in the production of chemical compounds important for normal growth.
9. Increased susceptibility to extreme temperatures: Drought stress can make trees more sensitive to extreme temperatures, be it cold or heat.
10. Root loss and soil changes: Drought stress often causes trees to lose some of their roots. This not only affects water absorption, but can also stabilize the soil and contribute to erosion.

Measures to mitigate drought stress in trees may include providing adequate irrigation, adjusting tree care practices, mulching, selecting drought-resistant tree species, and minimizing soil compaction. It is important to understand trees' water needs and provide supplemental irrigation during dry periods to maintain their health and vitality.