Gnats in Orchid Soil

Fungus Gnats

• Fungus gnats themselves do not harm orchid plants. However, their larvae feed on root systems and leaves. Gardeners may find their fungus gnat problem escalate quickly, because females lay up to 200 eggs during their one week lifespan. Also, gardeners make their fungus gnat problem worse by improperly watering their plant. Female fungus gnats prefer to lay eggs in soil that is moist. It is important for gardeners to treat their fungal gnat problem and employ different orchid care practices.

Bacterial Management

• Treat fungal gnat larvae with soil drench that contains bacillus thuringiensis israelensis. Bacillus thuringiensis israelensis causes a bacterial infection in the larvae's gut, which prevents the pest from eating. Eventually, the larvae dies in the potting medium. To use a soil drench, make sure that the insecticides absorbs into at least the first 3 inches of top soil where most of the larvae live. Because this drench is effective for 48 hours, gardeners may reapply several times during the year.

Repotting

• Repot your orchid after killing fungal gnat larvae. Fungal gnat larvae eat the organic material out of potting soil, so it is important to replenish the nutrients taken out of the medium with new soil. Mix up your own orchid mixture based on the type of orchid you are growing. For example, gardeners should mix up a fine mix of potting soil for slipper orchids, most oncidiums or miltonias, according to the National Gardening Association. Blend together one part fine charcoal, four parts fine-grade fir bark and one part perlite. A medium mix for mature orchids is made with one part medium charcoal, one part perlite and four parts medium grade fir bark.

Prevention

• Allow the top of your orchid's potting soil dry out in between watering. To know when to water your orchid, push your finger into the first inch of top soil. If the soil is dry, apply water until it drains out from the draining holes. Keep a saucer filled with pea gravel underneath the pot to aid in drainage and humidity. In addition, reduce your fertilizer applications until your orchid gets used to the new potting medium.