Common issues with Australian native plants and how to treat them
While tough, native plants are not immune to problems. Issues can arise from environmental factors such as soil type, drainage or weather extremes; garden conditions including overcrowding or limited airflow; or well-intentioned gardener mistakes like overwatering or overfeeding. In some cases, what looks like a problem is simply a natural adaptation or stress response rather than a sign of failure.
The challenge for gardeners is learning how to tell the difference and understanding that while some issues resolve quickly, others require patience, persistence and ongoing observation rather than a single fix.
The issues below are among the most common faced by home gardeners. While some can be persistent, many can be managed naturally and at low cost with the right approach.
1. Scale insects on gum trees with ants and sooty mould
Scale insects are one of the most common and most challenging issues gardeners face with gum trees (Eucalyptus, Corymbia and Angophora species). Because gum trees are long-lived, woody and often large, scale problems can be slow to resolve and require patience rather than quick fixes.
How to spot it
On gum trees, scale insects appear as small, immobile bumps along stems, branches and sometimes leaf veins. They can be difficult to notice early, particularly when infestations begin high in the canopy.
Common signs include:
- Ants travelling repeatedly up and down the trunk or branches and increase in flies
- Sticky residue (honeydew) on leaves, bark, paving or surfaces below the tree
- Leaves looking dull, stressed or slightly distorted
- A black, soot-like coating may develop on leaves and branches known as sooty mould
Why it happens
Scale insects feed by drawing sap from the tree, gradually weakening it. They excrete honeydew, a sugary substance that coats plant surfaces. Ants are attracted to this honeydew and will actively protect scale insects from predators. On gum trees, scale outbreaks are often linked to stress factors like extended drought or heat, compact or waterlogged soil, root disturbance or reduced airflow.
Sooty mould grows on the honeydew left behind by scale. The sooty mould can block light and add to overall stress and make the tree go a dark, ashen colour.
What to do
Managing scale on gum trees is rarely a one-off task. It usually requires ongoing monitoring and layered responses, particularly on established trees.
Practical steps include:
- Interrupt ant access using physical barriers or strong tape applied in a band, sticky side out around the trunk
- Manually removing scale with a brush where accessible
- Gently washing affected foliage to remove honeydew and sooty mould
- Avoiding broad-spectrum insecticides, which kill beneficial predators and can worsen long-term imbalance
For large gum trees, complete eradication is often unrealistic. The goal is to reduce pressure on the tree, support its recovery and allow natural predators to re-establish over time. Progress is often slow and uneven and setbacks can occur during hot, dry periods.
How to tell if it’s improving or if intervention is needed
Signs of improvement include reduced ant activity on the trunk, cleaner new growth, fewer new scale deposits and a gradual decline in sooty mould.
Signs the issue may be escalating are widespread yellowing or drop of leaves, progressive branch dieback and scale continuing to spread despite ant control.
A gum tree showing some scale is not necessarily unhealthy. A gum tree under sustained stress is more vulnerable and addressing that stress is often more effective than treating the insects alone.
2. Yellowing leaves on native plants
Yellowing leaves are one of the most common concerns gardeners have with native plants. While it can look alarming, yellowing is often a response to conditions rather than a sign that something is fundamentally wrong.
How to spot it
Leaves gradually lose their green colour and turn pale yellow, often starting with older or lower foliage. Yellowing may appear evenly across the plant or in patches and can occur with or without leaf drop. In some cases, yellow leaves remain firmly attached. In others, they fall soon after changing colour.
Why it happens
In native plants, yellowing leaves are most commonly linked to water and soil conditions, rather than nutrient deficiency.
Common causes include:
- Overwatering, particularly in heavier soils
- Poor drainage leading to oxygen-starved roots
- Soil that is too rich or regularly fertilised
- Recent planting or root disturbance
When soils are too wet or nutrient-rich, roots of Australian native plans can struggle to function efficiently. In response, the plant sheds or discolours leaves to reduce demand and rebalance itself. Yellowing can also occur as a normal adaptive response, especially during establishment, seasonal change or periods of environmental stress.
What to do
The most effective response to yellowing leaves is often to do less, not more, but it helps to know what that looks like in practical terms.
Practical steps include:
- Check soil moisture before watering by inserting a finger or wooden skewer into the soil to a depth of several centimetres. If the soil feels cool and damp below the surface, watering can wait. Native plants generally prefer soil that dries slightly between waterings rather than staying constantly moist.
- Reduce watering frequency rather than volume. Water deeply, then allow time for the soil to dry before watering again. Frequent light watering is more likely to cause problems than occasional deep watering. Using a terracotta olla can ensure water to the roots where it's needed most.
- Improve drainage where water lingers. In garden beds, this may mean loosening compacted soil with a gardening fork, incorporating coarse sand or gravel, or slightly raising the planting area. In pots, ensure drainage holes are clear and consider switching to a free-draining native potting mix if water sits in the pot after watering.
- Avoid fertilisers unless a clear deficiency is present. Many native plants are sensitive to excess nutrients, particularly phosphorus. Feeding a stressed plant often increases leaf yellowing rather than correcting it.
3. Slow or stalled growth in native plants
Slow growth is one of the most misunderstood behaviours in Australian native plants. Many gardeners assume something is wrong when a plant appears unchanged for weeks or even months, but in most cases, this is part of a normal establishment process.
How to spot it
The plant remains alive and upright but shows little to no visible growth above ground. Leaves may look healthy, stems remain firm and there are no obvious signs of decline — just a lack of progress. This is especially common in the first year after planting.
Why it happens
Many Australian native plants prioritise root development before above-ground growth. This allows them to anchor deeply, access moisture and survive long-term environmental stress.
Other contributing factors include:
- Seasonal growth patterns, where plants grow in bursts rather than continuously
- Cooler weather or shorter days
- Low-nutrient soils, which slow visible growth but support longevity
- A sign the plant is investing energy where it matters most
What to do
In most cases, the best response is patience.
Practical steps include:
- Maintaining consistent care rather than changing conditions frequently
- Avoiding unsuitable fertilisers, which can force weak growth
- Allowing the plant time to establish before expecting visible progress
Resist the temptation to “fix” slow growth. Many native plants respond poorly to being pushed.
How to tell if it’s improving or if intervention is needed
Signs of healthy establishment include firm stems, leaf retention and eventual bursts of new growth when conditions suit. Intervention may be needed if slow growth is accompanied by wilting, leaf yellowing, dieback or signs of root stress.
4. Leaf drop after planting
Leaf drop shortly after planting can be alarming, but it is one of the most common and least understood responses in native plants.
How to spot it
Leaves fall soon after planting, sometimes rapidly, leaving stems sparse or bare. The plant may look worse before it looks better.
Why it happens
This is usually transplant shock. When roots are disturbed, the plant reduces leaf area to lower water demand while it re-establishes underground. This response is common in trees and shrubs and does not necessarily indicate failure.
What to do
The key is to stabilise conditions rather than intervene aggressively.
Practical steps include:
- Watering consistently but not excessively
- Avoiding fertiliser and heavy pruning
- Allowing time for roots to re-establish
Frequent changes to watering, feeding or position can prolong stress.
How to tell if it’s improving or if intervention is needed
Signs of recovery include new buds forming, fresh shoots emerging and stems remaining flexible and green. Concern is warranted if stems dry out completely, snap easily or show no signs of regrowth over time.
5. Sawfly larvae on native plants
Sawfly larvae are one of the most common and confronting chewing pests gardeners encounter on Australian native plants. Because they feed quickly and visibly, they often cause panic, but many native plants can recover well when the issue is managed.
Sawfly larvae are soft-bodied, caterpillar-like insects that feed in groups. They are most commonly found on new growth and along leaf edges.
Common signs include:
- Rapid defoliation, sometimes occurring overnight
- Clusters of larvae feeding together on the same plant
- Larvae raising their tails in unison or releasing a fluid when disturbed
The speed and coordination of their feeding is often what alerts gardeners to their presence.
What they are
Despite their appearance, sawfly larvae are not caterpillars. They are the larval stage of sawflies, which are more closely related to wasps than butterflies or moths.
Many sawfly species found in Australian gardens are native and their life cycles are closely tied to native plants such as grevilleas, bottlebrushes, lilly pillies and eucalypts. As part of the ecosystem, they play a role in food webs and are prey for birds and predatory insects.
Why it happens
Sawfly larvae are attracted to soft, fresh growth, which is easier to feed on. Outbreaks often occur in spring or after rain when plants produce new shoots.
Heavy infestations are more likely when plants are already under stress, there is limited predator activity and conditions favour rapid larval development
What to do
Sawfly larvae are best managed with targeted, low-impact action rather than chemical control.
Practical steps include:
- Manually removing larvae by hand or with a gloved finger
- Monitoring plants daily during active periods
- Encouraging birds and beneficial insects by avoiding broad-spectrum sprays
How to tell if it’s improving or if intervention is needed
Signs the situation is resolving include feeding slowing, larvae disappearing and new growth emerging after damage.
Intervention may be needed if plants are repeatedly stripped before they can recover, young or newly planted natives are affected and overall plant health begins to decline.
Learning when to act and when to wait helps keep both plants and ecosystems in balance.
The issues covered here are some of the most common challenges gardeners encounter with native plants. They’re also among the most manageable. In most cases, once you understand what’s causing the problem, the response is straightforward and doesn’t require expensive products or drastic intervention.
Knowing what can go wrong — and why — helps build confidence. It allows you to recognise when a plant is simply adjusting, when it needs a small change in conditions and when patience is the best response. Over time, this understanding leads to stronger plants, fewer interventions and a more resilient garden overall.
