How to keep mould off your mandevillas and frangipanis in the humid Australian Summer

Backyard Basics with Paul Green

As the mercury soars and humidity wraps around our gardens like a damp doona, Australian gardeners face the perennial challenge of mould on tropical favourites. Both mandevillas and frangipanis are renowned for their lush blooms and vibrant displays, but they are especially susceptible to fungal issues in these sticky conditions. With the right approach, however, you can protect your plants and keep your garden looking a million bucks all summer long.

Why Does Mould Flourish in Summer?

Mould loves warm, moist environments. When summer brings high humidity and regular downpours or heavy morning dew, it creates the perfect storm for fungal spores to settle and multiply on leaves, stems and even flowers. The result? Unsightly powdery coatings, leaf spots, and sometimes, leaf drop. Prevention is the key.

Top Tips to Prevent and Treat Mould

Improve Air Circulation

Start by pruning. Remove crowded branches and spent flowers to open up the canopy of your mandevillas and frangipanis. Good airflow dries out moisture quickly, making it less inviting for mould. If your plants are close together, consider spacing them out or trimming foliage to allow the breeze through.

Water Wisely

Water at the base of your plants early in the morning. Avoid wetting the leaves, especially in the evening, as lingering moisture overnight is a mould magnet. Install a drip irrigation system or use a watering can with a long spout for precision.

Mulch with Care
A healthy layer of mulch helps retain soil moisture and suppress weeds, but mulch piled too close to stems can trap humidity and risk fungal problems. Leave a gap around the base of your mandevillas and frangipanis to promote drying.

Choose the Right Fertiliser

Overfeeding can lead to lush, soft growth that is more vulnerable to mould. Use a slow-release, balanced fertiliser and avoid high-nitrogen formulas during humid periods.

Monitor for Early Signs

Check your plants weekly for powdery patches, yellowing, or black spots on leaves. Remove any affected foliage promptly and dispose of it in the bin, not your compost heap, to avoid spreading spores.

Natural Remedies

Spray leaves with a homemade solution of one part milk to nine parts water, or use a commercial eco-friendly fungicide. Neem oil is also a good option, but always follow the label instructions and avoid spraying during the heat of the day.

Keep the Garden Tidy

Fallen leaves and flowers can harbour mould. Regularly sweep up plant debris from the footpath, garden beds, and under your ute if you’re carting garden waste around. Dispose of it properly.

Extra Aussie Tips

Position your mandevillas and frangipanis where they’ll get plenty of morning sun, which helps dry foliage quickly.

If humidity is especially persistent, consider running a small fan (outdoor rated) near your plants for a few hours each arvo. Sounds a bit over the top but it does work.

Don’t forget to inspect your plants after storms or heavy rain – these are prime mould moments.

Visit your local nursery or chemist for fungicide advice tailored to the conditions in your area.

When to Call in the Experts

If mould persists despite your best efforts, it may be time to consult a professional. Local garden centres or horticultural experts can recommend specific treatments suited to your climate and garden setup.

With a proactive approach and a few simple tweaks to your gardening routine, you can keep mould off your prized mandevillas and frangipanis—even in the stickiest Aussie summer. The key is vigilance, good hygiene, and timely action. Happy gardening!