Hydrangea macrophylla Magical Amethyst Tiny Black Flies - Causes & Fixes

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Fungus Gnats

The tiny black flies are likely fungus gnat adults, which breed in the moist organic matter of the potting soil. Their larvae feed on the fine root hairs of the Hydrangea, which can lead to reduced vigor and nutrient deficiency.

Very Common

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How to confirm: Set a yellow sticky trap near the soil surface to confirm the presence of flying adults.

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1 Deploy yellow sticky traps to capture the adult flying gnats and break the breeding cycle.

Super Ninja Fungus Gnat Traps - 30 Pack

30 pcs

In Stock

2 Allow the top inch of soil to dry out completely between waterings to disrupt the larvae's moist breeding environment.

GROWIT Analog Soil Moisture Meter

Water Meters

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3 Apply a microbial-based liquid drench to target larvae in the soil and promote a healthier root zone.

FoxFarm Bush Doctor Microbe Brew 1 Gallon

3.8 L

$115

In Stock

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Overwatering and Soil Compaction

Hydrangeas require consistent moisture, but excessively wet or poorly draining soil creates the perfect aerobic environment for fungus gnat larvae to thrive. This constant dampness can also lead to root suffocation in this specific cultivar.

Very Common

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How to confirm: Stick your finger two inches into the soil to check if it remains saturated even days after the last watering.

build How to fix it

shopping_cart Recommended Products

1 Reduce watering frequency and allow the top inch of soil to dry out completely to disrupt the fungus gnat life cycle.

GROWIT Soil Moisture Meter SMM-V3

Water Meters

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2 Apply a biological control to eliminate existing larvae and adults, such as Bonide Captain Jack's Neem Oil.

Bonide Captain Jack's Neem Oil 32 oz

0.9 L • 1 pcs • Organic

$10

In Stock

3 Repot the hydrangea in a well-aerated, fresh medium containing perlite to improve drainage and prevent future soil compaction.

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Decomposing Organic Matter

High levels of uncomposted peat moss or decaying mulch in the Hydrangea pot provide a nutrient-rich breeding ground for flies. As this organic material breaks down, it attracts moisture-loving insects.

Common

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How to confirm: Inspect the top layer of the soil for any visible mold or heavy accumulation of decomposing leaf litter.

build How to fix it

shopping_cart Recommended Products

1 Remove the top layer of decomposing organic matter or mulch from the soil surface to eliminate the breeding ground for the flies.

2 Apply a biological control like Bonide Captain Jack's Neem Oil to treat the larvae and adults, and ensure the soil surface is clean.

Bonide Captain Jack's Neem Oil 32 oz

0.9 L • 1 pcs • Organic

$10

In Stock

3 Use yellow sticky traps to capture the adult flies and prevent further reproduction cycles.