Scarborough's gardens sit on some of the most exposed residential land in Perth. Trees here can look settled from the street while coping with conditions that would test them anywhere. This guide explains what those conditions do, how to read the signs of stress, and what pruning, watering and planting choices make the biggest difference.
Three pressures on a coastal tree
Salt on the wind
Waves breaking along Scarborough and Trigg beaches throw fine droplets of sea water into the air. The afternoon sea breeze carries them inland, where they settle on leaves and stems. As the water evaporates, salt is left behind. It draws moisture out of leaf tissue and can damage the tips and edges of leaves.
The effect is strongest on the windward side of a canopy and on the highest, most exposed branches. You can often see it from the street: trees that are lush on the sheltered side and brown, thin or bare on the side facing the ocean. Over years, salt pruning shapes trees into a wind-swept profile, leaning away from the sea.
Salt also builds up in the soil if rain is light and watering is shallow. Winter rain usually flushes it through the sand, but in dry spells the root zone can become salty enough to stress less tolerant species.
Wind
Wind is the second pressure. The sea breeze that arrives most summer afternoons is steady and drying. Winter fronts bring stronger, gusty winds, often from the west and north-west. Both affect trees in several ways.
Wind dries out leaves faster than roots can replace the water, especially in sand. Constant movement also stimulates trees to put more growth into thicker trunks and roots and less into height, which is why exposed trees are often shorter and stouter than the same species inland. Large, dense canopies catch more wind, putting heavy loads on limbs and roots, particularly during winter storms.
Sand over limestone
The third pressure is under the ground. Scarborough sits on coastal sand dunes, ranging from pale, lime-rich sand near the beach to yellower sand further inland, all over limestone that can be close to the surface.
Sand drains quickly and holds very little water or nutrients. Roots spread wide to find what they need. Limestone limits how deep they can go, and the alkaline soil can make it harder for some species to take up iron and other trace elements, which shows as yellowing between leaf veins.
Together these factors mean coastal trees are often shallow-rooted, nutrient-poor and water-stressed through summer, then loaded by wind and wet sand in winter.
Reading the signs
Most problems are easier and cheaper to fix early. Walk around your trees a few times a year and look for:
- Brown or burnt leaf edges and tips, especially on the ocean side. A little is normal on the coast. Spreading damage or whole branches browning off is worth a closer look.
- Dead branches in the canopy, particularly large ones over roofs, paths or play areas.
- Thin canopies where you can see much more sky through the tree than you used to.
- Yellowing leaves with green veins, which often points to nutrient uptake problems in alkaline sand.
- Cracks, splits or loose bark on the trunk or main limbs, or a fork where two stems press tightly together with bark trapped between them.
- Lifting soil, cracked paving or a new lean at the base, which can indicate root movement.
- Fungal growths at the base or on the trunk, which can signal decay.
- Small round holes in the bark of susceptible trees, which may indicate borer activity. Perth is under a quarantine response to the polyphagous shot-hole borer; if you suspect it, report it to the Department of Primary Industries and Regional Development (DPIRD) rather than moving wood.
If you see something that worries you, a contractor can take a look while quoting other work, or you can engage an arborist for a formal assessment if you need a written report.
Pruning for the coast
Pruning is the main tool for keeping coastal trees safe. Done well, it reduces wind load and removes dead wood before it falls. Done badly, it can make things worse.
Clean out the dead wood regularly. Salt and wind kill twigs and small branches every year. Removing them every couple of years keeps the canopy healthier and safer.
Thin rather than top. Thinning removes selected branches from inside the canopy so wind passes through. Topping cuts branches back to stubs, which triggers dense, weak regrowth that catches more wind and burns in the salt. It is one of the most damaging things that can be done to a coastal tree.
Reduce end weight on long limbs. Long, horizontal limbs act like levers in strong winds. Shortening them back to a suitable side branch can reduce the risk of failure without changing the look of the tree much.
Keep the windward side. It is tempting to cut off the burnt, scrappy growth on the ocean side. But that growth shelters the rest of the canopy. Remove what is dead and leave live growth in place where possible.
Time heavy work sensibly. Late autumn, before the strongest winter fronts, suits a lot of preventive pruning. Very hot, dry periods are best avoided for heavy cuts.
Water, mulch and soil
Healthy, well-watered trees cope with salt and wind much better than stressed ones. In Scarborough's sand, the difference that water and mulch make is large.
Water deeply, less often. A long, slow soak that wets the sand well below the surface encourages deeper roots. Short, frequent sprinkles keep roots shallow and can concentrate salt near the surface. Follow Water Corporation's current watering rules and, if you have a bore, the rules that apply to it, including the winter sprinkler switch-off.
Mulch the root zone. A layer of coarse organic mulch over the root zone, kept clear of the trunk, slows evaporation, cools the sand, and slowly adds organic matter. Chipped material from tree work makes good mulch once it has aged a little.
Improve the sand gradually. Adding compost and soil improvers to planting holes and garden beds helps sand hold water and nutrients. A wetting agent can help water soak into sand that has become water-repellent over summer.
Go easy on fertiliser. Many WA native plants are sensitive to phosphorus. Use products suited to the species, and avoid heavy feeding that pushes soft growth into a salty wind.
Choosing trees that cope
If you are planting new trees, choosing species that tolerate salt and wind saves a lot of trouble later. Local nurseries in the northern suburbs can recommend options for your exact spot, but the following are commonly suggested for exposed coastal gardens in Perth:
- Rottnest Island pine (Callitris preissii), a hardy native cypress for windy sites
- Rottnest Island tea tree (Melaleuca lanceolata), a tough small tree that handles salt well
- WA peppermint (Agonis flexuosa), the familiar weeping street and garden tree, best a little back from the front line
- Coastal wattles native to the area, for fast shelter, although they are shorter-lived
- Norfolk Island pine, very salt-tolerant but very large; only for big spaces well away from buildings
Think about mature size before planting. A tree that suits a pot on the nursery bench may be twenty metres tall in a few decades. Allow room from the house, pool, pipes, paving and power lines, and check that the species is not an environmental weed in local bushland.
Planting a screen of tough shrubs on the windward side can shelter more sensitive trees behind it. Many Scarborough gardens use coastal hedges along front fences for exactly this reason.
A year on the coast
Late summer and autumn. Check trees for dead wood and drought stress after the hot months. Deep-water stressed trees within the rules. Book preventive pruning and reductions before winter.
Winter. Watch for wind damage after fronts. Keep clear of hung-up branches and call a contractor for anything loaded or broken. Plant new trees once the rains have soaked the sand.
Spring. Feed lightly where appropriate, refresh mulch, and check new plantings for salt burn as onshore winds pick up.
Summer. Water deeply and early in the morning, within the rules. Avoid heavy pruning in heatwaves. Keep an eye on dense hedges and screens drying out.
Good coastal tree care is mostly small, regular jobs: a deep watering, a top-up of mulch, a dead branch removed before it falls. If a tree has outgrown its space or is showing serious stress, the tree lopping, pruning and hedges and tree removal pages explain the options, and the cost guide has planning figures.