How to properly water city trees: Why they suffer from drought and how you can help

Our urban trees play a vital role in regulating the urban climate and making our cities more livable. When the trees are healthy, we humans are healthy too. However, the living conditions of urban trees differ significantly from those in forests or rural areas.
And in this article you will learn more about the Challenges of urban trees. 

Key facts at a glance

• Urban trees suffer more from drought than trees in natural locations.
• Compacted and sealed soils make water absorption more difficult.
• Young trees in particular need regular watering.
• Slow and deep watering is more important than frequent small amounts of water.
• Watering the surface often doesn't reach the roots sufficiently.
• Mulch and healthy soils help to retain moisture for longer.
• Irrigation bags can release water slowly and in a targeted manner to the soil.
  Acting early helps to avoid long-term damage.

Why city trees suffer particularly from drought

Urban trees grow under significantly more difficult conditions than trees in natural habitats or forests. The available root space in cities is often severely limited. Streets, sidewalks, buildings, and underground utilities leave little room for the roots.

In addition, sealed and compacted soils contribute to the problem. This makes it harder for rainwater to seep into the ground, and it often doesn't penetrate deep enough into the root zone. At the same time, asphalt, concrete, and building facades heat up considerably in the summer, further increasing the ambient temperature.

As a result, many urban trees are more susceptible to drought stress than trees in more natural soils. This becomes particularly problematic during prolonged periods of heat with little rainfall.

How can you recognize drought stress in urban trees?

Many trees show Drought stress Initially, it develops gradually. Typical signs can include:

• brown or withered leaves
• rolled leaves
• premature leaf fall
• dry branches or shoot tips
• smaller or limp leaves
• light crowns
• weak growth

It is important to note that not every weakened tree is necessarily sick. Often, trees initially react to persistent water shortages or poor soil conditions.

How often should city trees be watered?

How much water a tree needs depends on various factors. These include:

• Age of the tree
• Tree species
• Location
• Ground Condition
• Temperature and precipitation

Young trees, especially in their first few years, require regular watering because their root systems are not yet deep enough. During prolonged dry periods, a young tree can need significantly more than 100 liters of water per week. Older trees usually need less frequent watering, but they also benefit from additional watering during periods of extreme heat.
The general rule is: it's better to water less frequently but thoroughly than to distribute only small amounts of water daily. 

How do you water city trees correctly?

The amount of water is not the only crucial factor; the method of watering is equally important. Many people water too quickly or too shallowly. As a result, the water remains in the upper layers of soil and often evaporates after only a short time.

Slow and deep watering is better. This allows the water to penetrate deeper into the soil and reach the actual root zone. The following are helpful:

• slow irrigation
• larger quantities of water at longer intervals
• Watering in the early morning or evening
• Watering over a large area around the base of the tree
• Mulch layers to reduce evaporation
• It is also important not to water exclusively directly at the base of the trunk. Many fine roots are located in the outer area around the tree.

In this article you will find more information about the geeßen of trees.

Why superficial watering is often not enough

Short, superficial watering offers limited help to many urban trees. Especially on hot days, water evaporates very quickly from the surface. While the upper soil layers may appear moist, deeper roots remain dry. At the same time, small amounts of water often encourage shallow roots near the surface, which are particularly sensitive to heat and drought.

Deeper and slower watering, on the other hand, supports the development of more stable roots in deeper soil layers.

Which watering methods are suitable for urban trees?

There are various ways to water urban trees. Even simple methods can help reduce drought stress. Suitable examples include:

• Watering cans
• bucket of water
• garden hoses
• Irrigation rings
• irrigation bags

Particularly irrigation bags These can be helpful because they release water slowly into the soil over several hours. This allows the water to reach the root zone more evenly and be absorbed more effectively.

How much water does a city tree need?

The water requirements of a tree cannot be determined in general terms. Young trees usually need water much more frequently than older trees.
As a rough guide, young urban trees often need between 75 and 200 liters of water per watering during dry summer months. However, the actual soil moisture and the duration of the dry period are always crucial factors.

Typical mistakes when watering city trees

Many damages are caused not only by drought itself, but also by improper irrigation. Common mistakes include:

• Watering too frequently with small amounts: Small amounts of water often do not reach deeper roots sufficiently.
• Water only directly at the base of the trunk: Many fine roots are located further out in the area of ​​the tree disc.
• Water at midday: Water evaporates faster in high heat.
• Ignore compacted soils: Even regular watering only helps to a limited extent if water can barely penetrate the soil.
• Reacting too late: Many damages only become visible when parts of the crown are already affected.

How mulch and soil care help city trees

Not only is water itself important, but also the soil's ability to retain moisture. Healthy soil is therefore a crucial foundation for resilient urban trees. Mulch For example, the following can help:

• to reduce evaporation
• to protect the floor from overheating
• to promote soil life
• to retain moisture in the soil for longer

Suitable materials include wood chips, leaves, or other organic mulch. However, some space should be left between the trunk and the mulch layer to prevent the bark from remaining constantly damp. Complementary greenery around the base of the tree can also help to shade the soil and reduce drying out. At the same time, plant diversity and organic material promote more active soil life.

Additionally, organic soil improvers such as worm compost can support soil structure and contribute to long-term water retention. Organic matter improves the soil's ability to retain moisture and nutrients more readily.

Supporting city trees together

Many cities and towns are now calling on residents to help water city trees during dry periods. Especially in hot summers, community involvement can help preserve trees in the long term.
Often, simply watering individual trees in the neighborhood regularly is enough to significantly reduce drought stress. Young street trees, in particular, benefit from additional watering.

Use rainwater for city trees

Especially in cities, a large portion of rainwater is quickly drained away through sewers. At the same time, many urban trees suffer from water scarcity. Therefore, it is worthwhile to use rainwater locally whenever possible. Rain barrels, cisterns, or shared water tanks can help to temporarily store precipitation and use it later for irrigation. This saves valuable drinking water and improves the water supply for trees during dry periods.

You can find more information in the article. Using rainwater for trees: Why every drop counts. The following are also very inspiring: Watering can heroes, which provide water tanks for the trees in some cities.