Thankfully, most houseplants don’t mind if you cut back on their water a bit. Truth be told, many plant parents are guilty of watering their plants more than they should. So much so, that overwatering is a common cause of death in houseplants!
In a similar method to hydrogen peroxide or Bti, a neem oil drench can also be applied to the infected soil to kill fungus gnats. Do not use straight concentrated neem oil though! Create and apply a dilute neem oil solution by following the manufacturer’s instructions on the neem oil product you select. Watering with a dilute neem oil solution can help to kill fungus gnats, and also repel them in the future.
After potting your houseplant, consider adding a layer of horticultural sand (not play sand!) to the top of the soil. You can water the plant through the sand, and meanwhile it will deter fungus gnats from laying eggs in the pot. In addition to sand, there are other soil-topping products like this one (made from crushed recycled glass) that are specially made to eliminate fungus gnats from your potted plants.
When potting up a new houseplant, use a reputable quality bagged potting soil. One that has been pasteurized or sterilized shouldn’t have live eggs, larvae, or flies in it. Avoid using soil from your yard, as it may bring unwanted pests inside along with it.
As we’ve already established, fungus gnats love moist soil – and need it to breed! Therefore, overwatering your plants can easily lead to a fungus gnat problem. To prevent and battle fungus gnats, avoid overwatering your plants in the first place. Only provide water when the top couple inches of soil has dried out. Remember, that top shallow soil is where the fungus gnats are drawn to!
When you bring home a new houseplant, look for the presence of fungus gnats. Unfortunately, only the flies will be obvious since the larvae or eggs are very difficult to detect. It is a good idea to keep new plants away from your other houseplants for several days to monitor, especially if you have suspicions that they may be infected. Remember, fungus gnats don’t typically fly long distances unless they have to!
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At the first sign of a fungus gnat issue, this should be the initial step. Allow the top few inches of the plant’s soil to dry out. This will make the soil unattractive to adult flies, preventing them from laying more eggs. If you’re lucky, this can kill a lot of the eggs and larvae too! Furthermore, eliminate standing water. This includes in the pot drainage tray, or even from other sources nearby – such as leaky pipes, condensate puddles, and so on.
Fungus gnats reproduce by laying eggs in the top couple inches of damp soil. The eggs hatch into larvae, the larvae feed on organic matter within the soil for 2 weeks, and then they pupate. A couple of days later, the adult flies emerge and start buzzing around. You’ll commonly see fungus gnats hanging out on the soil surface, edge of the pot, or maybe around the drainage holes of the pot. They most often only fly in short bursts, and otherwise crawl around.
Read along to learn 5 easy and non-toxic ways to get rid of fungus gnats in your houseplants, plus a few tips on how to prevent them in the first place!
While a wet soil can be a haven for Fungus Gnats, there are a couple of soil drenches that can be used to eliminate populations that are already in the soil.
As they say in the classics, prevention is always better than a cure, here are some tips to avoid a full-on “Gnat Attack”.
- Don’t overwater –Excessive watering can lead to the growth of algae in saucers and on the surface of the soil which fungus gnats will feed on. This is particularly important overwinter, when the irrigation requirement from indoor plants is much lower than other seasons. Overwatering can also lead to weakness or rot in plant roots, making them “soft targets” for fungus gnat larvae.
Remember, you can only use one of these methods, as the Neem-Oil drench may kill the beneficial nematodes also.
If you haven’t noticed the larvae in the soil, or the adults buzzing around but you think there may be gnats in your plants, before you undertake unnecessary treatment, there’s an easy gnat test that anyone can do – cut a slice of raw potato and leave on the surface of those pots potentially harbouring these houseguests. Leave overnight and check for the presence of the larvae on the potato the next morning – gnats are attracted to starch and cannot resist this tasty treat!
Most house guests are welcome, especially those that love and admire our indoor plants as much as we do, but there is one group of gate crashers that every gardener dreads. Fungus gnats (Bradysia sp.) are often first noticed in our houses or greenhouses in their adult form – small (about 3mm long) black to dark grey mosquito-like flies hovering in small groups around our beloved indoor plants. And while the adults can be an annoyance, it is the tiny (less than 5mm), black-headed, soil-dwelling larvae that can do some serious damage to the roots and stems of a huge range of indoor plants, chomping through the base of cuttings, soft stems and roots with a voracious appetite.
Fungus Gnats are the bane of many gardeners with indoor plants, especially over the cooler winter months. Jane gives us some tips on how to avoid a gnat attack at your place, and what to do if you already have these unwelcome house guests
Fungus gnats love rich, damp soils and given the right conditions, fungus gnats can complete their lifecycle from egg to adult in about three weeks, with female adults capable of laying between 100 – 300 eggs at once. Because of this, it is possible that your pot plant may indeed be playing host to overlapping generations of Fungus Gnats at any given time, meaning swift control is required to prevent serious infestations. Their lifecycles can be easily interrupted and broken by allowing at least the top 10cm – 15cm of potting mix to dry out between waterings.
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Jane shares her favourite tips and techniques for getting rid of an unwelcome house guest, fungus gnats