Orange has a fantastic collection of street trees. In dry times these trees need some extra care. When needed, Orange City Council’s tree team concentrates its efforts on watering the youngest which are the most at-risk of damage. Strategies such as placing slowly-dripping water drums alongside young trees are used.
Residents can help preserve their local streetscape by ‘adopting’ a tree near their home. Mature trees can have large water requirements and may lose hundreds of litres of water every day (transpiration) through their leaves. Trees will experience stress if there is not enough water in the soil to replace the water lost through the leaves. Continued stress can lead to serious problems for trees. Supplementary watering can assist in maintaining a tree’s health. Landscape trees commonly grown in Australia originate from many different climate zones and have different water needs.
How can I tell if a street tree is ‘stressed’?
Signs of water stress include:
- wilting foliage
- marginal leaf scorch
- lack of new growth in spring
- dieback of leaves, twigs and branches.
The premature shedding of leaves without the appearance of the wilting or leaf scorch is another response to water stress.
How should I water a street tree?
The majority of a tree’s fine, water-absorbing roots are located in the top 10 to 30 cm of soil. As a rule of thumb, watering mature trees deeply every week or two during dry periods throughout the growing season (September through to April) can be beneficial, especially for stressed trees, and may assist in keeping trees alive during times of drought. However, excess water is just as bad for trees as too little water.
The adage ‘water deeply, less frequently’ is correct. Slow watering that provides an even coverage and targets the absorbing roots is the key to successful watering and encourages a deep root system. Frequent, light watering encourages shallow root development. Shallow roots are more susceptible to summer heat stress, winter cold injury and drought stress.
Watering is best with a low pressure system such as :
- drip irrigation
- a soaker hose
- water poured slowly from a bucket.
Apply enough water to moisten the soil to a depth of 40cm. Depending on the trees’ size, method of irrigation and soil type, this may take several hours. Avoid creating water runoff as this wastes water and doesn’t allow the water to reach the targeted area.
How close to the tree should I water?
Watering near the trunk isn’t efficient. For most trees there are generally few water absorbing roots in this area. The best place to put water is in the ‘drip zone’ or ‘drip line’. The drip zone is an imaginary ‘doughnut’ shape on the ground under the branches directly under the outer edge of the leaf canopy. Trees like water in the same position every time. Don’t try to wet the entire root area. Instead concentrate the water in a shaded area and the tree will maintain its root activity there.
Using mulch is the most effective way to conserve water. Maintaining a 7cm to 10cm layer of mulch over the root zone can reduce the amount of water that is lost from the soil through evaporation. Mulch can conserve water by up to 70%, reducing the need for watering. Some organic mulches also have the benefit of adding nutrients to the soil as they break down and improving the soil structure, aiding in water and air penetration.
Keep mulch a minimum of 20cm away from the trunk. This space will allow for air circulation around the base of the plant and help avoid potential disease problems. The greater the area of root zone that is mulched and free of other plants, the less competition for water, air and nutrients and the more benefit to your tree. A properly mulched tree will have a layer of mulch in a doughnut shaped ring. The ring should extend out to the tree’s drip line if possible.
Download Orange Street Trees fact sheet which outlines its local street tree strategies.
Orange has 12,500 street trees. Download Orange Street Tree Master Plan which outlines a long term strategy for managing this valuable resource.