If you’re over fungus gnats, mealybugs or mites chewing through your pride and joy, diatomaceous earth (DE) is one of the simplest low-toxicity tools to add to your kit. Used properly, it’s effective, doesn’t create resistance, and slots neatly into an integrated pest management (IPM) approach. This guide shows you exactly how to use it in Australian conditions — safely, and without clobbering pollinators.
What DE actually is (and why the type matters)
Diatomaceous earth is a powder milled from fossilised diatoms (hard-shelled algae). For plant use, choose amorphous silica — not the calcined pool-filter grade that contains higher crystalline silica and is unsuitable for plants or people. Even food-grade DE is a fine dust: avoid inhalation and protect your eyes during use.
Key point: Choose amorphous DE for plants. Never use pool-grade DE on or around plants, animals, or people.
How DE works (and its biggest limitation)
DE works by physical contact. It abrades the insect’s protective cuticle and absorbs oils so the insect desiccates. It’s not a poison, and insects don’t develop resistance to it.
Limitation: it only works when dry and must contact the pest. Keep treated surfaces dry and re-apply after watering, heavy dew or rain.
When DE shines (and when it doesn’t)
Great for: soft-bodied crawlers — fungus gnats (top of soil), aphids (contact), mealybugs, spider mites, thrips (on surfaces), ants, cockroaches, slugs (when dry).
Not great for: pests shielded under thick waxy coatings you can’t reach, situations that stay wet, or flying pests that don’t land on treated surfaces. Re-apply after watering.
Pollinators & beneficials: DE is non-selective — it can harm beneficial insects on contact. Keep it off open flowers and avoid broadcasting dust on blooms. Target only the pest zones.
How to apply DE (two proven methods)
Target first (so you use less product and spare the good bugs), then choose one of the methods below.
1) Dry dusting (fastest)
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Isolate the plant if feasible.
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With a puffer or shaker, dust a light film on upper/lower leaf surfaces where pests crawl, stems, and the soil surface (for gnats).
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Leave dry for 24–48 hours; re-dust after watering or if the powder gets disturbed.
2) Micronised spray/slurry (best coverage on ornamentals)
Micronised DE can be mixed into water, sprayed for coverage, then allowed to dry so it leaves a fine film.
Nursery-tested recipe
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1 tbsp DE per 1 L water + 1 tsp soft/horticultural soap
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Shake and keep agitating (DE settles).
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Spray to full coverage, including undersides of leaves and the soil surface.
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Let it dry completely so the film forms.
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Repeat twice weekly for 2–3 weeks.
This slurry works because the kill happens after it dries — a fine film remains on surfaces the pests crawl over. Micronised, sprayable DE is designed for this.
Pest-by-pest playbooks (indoor & outdoor)
Fungus gnats (houseplants)
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Top-dress 2–3 mm of DE on the soil. For two weeks, bottom-water so the top stays dry.
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Add yellow sticky traps to catch adults; re-apply DE after any top watering.
Mealybugs & scale (citrus/ornamentals)
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Use the micronised slurry; spray to full coverage (leaf undersides, petioles, stems, soil).
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Repeat twice weekly for 2–3 weeks; wipe off dead residue after 3 days.
Spider mites & thrips (leaf undersides)
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Combine targeted dusting of leaf undersides plus the slurry to reach crevices.
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Allow plants to dry quickly in shade; re-treat weekly until pressure drops.
Aphids (veg & roses)
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First hose off colonies with water.
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Then dust stems/leaf undersides or apply slurry; keep away from open blooms.
Ants, roaches & slugs
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Perimeter dust where they travel (patios, pot feet, thresholds).
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Refresh after dew or rain and keep the powder dry.
Safety & compliance (Australia)
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Follow the label. Use only products sold and labelled for pest control; follow all directions and local regulations.
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Respiratory/eye protection: Wear a P2/N95 mask and eye protection when handling fine DE; avoid creating airborne dust; use outdoors or in well-ventilated spaces.
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Keep it off flowers to protect bees and beneficials. Target only pest pathways.
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Store sealed & dry. DE clumps when wet; efficacy returns once fully dry.
Why our Micronized & Sprayable DE is different
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Micronised particle size for smooth slurries and even films once dry.
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Works brilliantly for soil top-dress against gnats and as a dust for mealybugs/aphids/mites/ants.
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Free shaker with 5 L for easy perimeter dusting.
Shop: Dr Greenthumbs Diatomaceous Earth – Micronized & Sprayable (Pure Silica)
FAQs
Does diatomaceous earth really work on houseplant pests?
Yes — when it stays dry and contacts the pest. It kills by desiccation. Re-apply after watering.
Is it safe around kids and pets?
Use food-grade DE, avoid inhalation, and apply targeted amounts. Wear a mask/eye protection and keep out of reach of children and pets during application.
Can I spray DE? Doesn’t it need to be dry?
You can spray a slurry for coverage (micronised DE helps). The effect begins after it dries and leaves a film on surfaces.
Will DE hurt bees?
DE is non-selective and can harm beneficial insects on contact. Keep it off flowers and use it where pests travel (soil, stems), not on blooms.
How quickly does it work?
Expect results within about 48 hours when it’s dry and in contact with the insect. Coverage, humidity and pest pressure all play a role.
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