Caring for Trees in Long, Dry Heat

Knowing if a tree is drought-stressed

How do you know if your tree is suffering? Leaves lose their shine, change colour, wilt or curl up at the edges. They might go yellow or be smaller than usual, drop prematurely, or turn brown and stay on the tree. Sometimes we mistake this for ‘Autumn coming early’. A tree might appear to be surviving drought stress, but an extended dry period sets trees up for secondary insect and disease infestation. Check for signs of an insect attack, like the insects themselves and holes in leaves.

Caring for trees in heat

It’s easier for established trees to withstand drought, but most trees can use a little help in very hot, dry times. It’s important to eliminate anything that might further stress the tree including ivy, mistletoe and creepers. Clear an area around the base of the tree and avoid fertilizers. When it comes to watering, methods which apply water slowly, directly and at soil level are best. Sprinklers tend to soak the topsoil, but soaker hoses are an effective way to water trees. Being porous, they release water slowly. Create a dripline of soaker hose in a circle around the tree and allow it to run for a minimum of 1 hour at a time. The water needs to penetrate down to at least 6 inches. Trees prefer a good, deep soaking about once a week rather than superficial watering every other day. Shallow watering encourages roots to stay near the surface, whereas deep watering encourages strong, embedded, drought-resistant tree roots.

In addition to keeping the water up, it’s important to know that different tree species have different transpiration rates and react differently to drought stress. Australian trees are amongst the best at controlling water loss through their leaves during periods of low rainfall whilst maintaining fast growth rates. Species that have evolved in environments with more consistent and reliable rainfall patterns are not as well equipped to handle our hot dry weather and can be severely affected by drought stress.

Mulch is doing more work than you think

A 75-100mm layer of organic mulch applied around the base of a tree (keeping clear of the trunk) is one of the most effective things you can do to protect it during hot, dry periods. Mulch regulates soil temperature, retains moisture, suppresses competing weeds and gradually improves soil structure as it breaks down. In Canberra’s summer heat, it can make the difference between a tree that struggles and one that thrives. Avoid piling mulch against the trunk. It traps moisture and encourages rot and pest activity at the base. Keep a clear gap of at least 100mm around the trunk and spread the mulch out to the drip line where possible.

Tips for planting and maintaining new trees

While some trees are far better suited to hot conditions than others, remember that no tree is truly drought resistant. Any newly planted tree is more sensitive to soil conditions and will require additional care through its first 2 years of life. Here are some useful tips for looking after newly planted trees in hot, dry conditions.

• Water every 2 or 3 days for the first month until established.
• Water early in the morning or late in the evening to prevent evaporation from strong sun.
• A deeper soaking less often is preferable to lots of light, superficial waterings.
• Beware of over-watering in clay soils, as the clay can trap moisture and rot the roots.

When to call an arborist

Heat stress can trigger or accelerate a range of secondary problems that aren’t always easy to identify without training. If your tree is showing signs of distress, it’s worth getting a qualified arborist to assess it. In many cases early intervention is straightforward and cost-effective. Left untreated, heat-stressed trees become vulnerable to insect attack and fungal disease, which can turn a manageable situation into a more complex one. Gold Leaf provides tree health assessments in the Canberra region — contact us if you’re concerned about a tree on your property.