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Does Bottom Watering Prevent Gnats? Here’s how

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Bottom watering is an effective method in the fight against fungus gnats as it reduces the moist environment that gnats live in.

Bottom watering prevents gnats by reducing the moisture content at the surface of the soil. Fungus gnats live and reproduce in moist soil where they feed on damp, organic material. Watering from the bottom reduces the moisture content at the surface of the soil, hence deterring fungus gnats in potted plants.

Although fungus gnats are about ? inch long or less, these tiny creatures with long-legs can dramatically damage the healthy roots of your houseplants if not handled on time. 

This article describes how bottom watering can effectively prevent gnats from doing it correctly so that gnats will no longer want to nest in the soil.

How Does Bottom Watering Prevent Gnats?

How bottom watering prevents gnats

A house with houseplants is heaven to shore flies and gnats. 

Throughout the year, gardeners hear the buzzing or flying sound of these tiny yet annoying creatures all around their place. 

Fungus gnats belong to the family Mycetophilidae and Sciaridae, one of the pure insects.

These mosquito-like insects are considered one of the most dangerous pests of houseplants, both indoor and outdoor. 

Fungus gnats love moist and warm topsoil. Therefore, the best way to control them is by allowing the growing medium of your houseplants to dry up. 

One of the most effective strategies to prevent fungus gnats around your houseplants is by allowing the growing medium to dry up completely between watering, especially the topsoil.

The dry topsoil will minimize the survival of any eggs or larvae. 

Furthermore, dry topsoil will also reduce the attractiveness of your growing medium to future egg-laying female gnats. 

Bottom watering can significantly reduce the growth of these fungus gnats. 

In bottom watering, plants soak up the required water through capillary movements. 

Unlike top watering, where gardeners drench the topsoil with water. 

With bottom watering, your houseplants will only soak up the required amount of water against gravity. 

The topsoil of your houseplants won’t be drenched in water and prevent the growth of gnats. 

See our our complete guide for bottom watering plants which gives easy to understand details with step by step instructions.

What is Bottom Watering?

Bottom watering is done by placing the plant in a tray of water at approximately 1 to 2 inches high. The water is then absorbed into the soil from the bottom up after which it is allowed to drain freely leaving the soil moist and aerated.

Bottom watering :

  • Stimulates healthy root growth
  • Prevents pests such as gnats
  • Prevents overwatering
  • Allows fresh air into the soil
Bottom watering plants infographic

What Type of Soil Condition Gnats Thrive in?

Adult fungus gnats, especially egg-laying adult females, are highly attracted to moist growing mediums of houseplants. 

Most egg-laying adult female gnats lay their eggs in growing mediums that have high amounts of peat moss and ambient temperature between  65 F to 75 F.

Larvae of fungus gnats commonly feed on fungi, algae, and soft roots. 

Thus, making the growing medium of houseplants heaven for laid eggs or larvae’s growth. 

Fungus gnats’ growth rate significantly increases during fall and winter. Because during these two seasons, some plant species such as succulents usually go into a state of dormancy. Cooler temperatures and shorter day lengths slow plant growth and minimize water requirements. 

However, the growing medium of houseplants remains extra moist during winter and fall because people always water more than the plants require. 

Bottom watering can help prevent overwatering your plant by ensuring that the plant roots get the water they need while not drenching the topsoil. 

Damp soil conditions tend to attract gnats.

Fungus gnats also thrive best in old or degrading growing mediums as they tend to retain more moisture. 

Therefore, it is highly advisable to change the soil of your houseplants after every two or three years. 

I use this Miracle-Gro Potting Mix from Amazon, which ensures my plants stay healthy long after repotting. Take a look and compare it to other potting mixes.

Miracle Grow Potting Mix

What Region of Soil Do Gnats Live in?

As we mentioned earlier in the article, adult fungus gnats are highly attractive to the moist growing medium, especially egg-laying females. 

Females lay their eggs (which later hatched into larvae) in the top 2 to 3 inches (5 cm to 7 cm) of the growing medium, depending on the dampness of the soil. 

Fungus gnats larvae usually live on the surface or inside plant tissue where they can easily feed on plant roots’ hairs and organic matter. 

The moisture level is the critical factor in determining where the gnats will be located. 

They may be living throughout your potting soil, even near the drainage of holes in your pots. 

Some gnats may also come out of the potting soil to feed on the dropped leaves lying on the surface of topsoil. 

Some gnats even tunnel into plants’ crowns to feed themselves. 

Fungus gnat larvae are highly attractive to growing mediums with “high” moisture levels and need decaying vegetation and fungi as the main food source to fully develop into healthy adults. 

As gnats mostly live in the top 2 to 3 inches of the growing medium where the soil is mostly moist, keeping this region dry or being moist for long periods can significantly decrease the growth of gnats.  

If you can keep the topsoil region from being overwatered or damp, new adult gnats, especially females, wouldn’t be attracted to your houseplants. 

That’s the prime reason why bottom watering is one of the most effective methods to prevent gnat infestation. 

How Are Gnats Bad For Plants?

Male adult fungus gnats don’t bite humans or leaves, however, they may drink water residing on the topsoil of your houseplants or on the leaves of your plants. 

In short, their presence is considered nothing other than a nuisance. 

However, adult egg-laying females can damage your houseplants by laying hundreds of eggs on the growing medium. 

During their short lifespans, female gnats can lay up to two hundred eggs into cracks and crevices of your potting soil. 

These eggs then hatch into translucent and legless larvae which can dramatically damage your plant’s development. 

Fungus gnats larvae can damage your houseplants in the following way:

They have a Voracious Appetite

Fungus gnat larvae have a voracious appetite and they can feed on a wide range of ornamental plants. 

The most common ornamental flowers that fungus gnats larvae prefer to devour includes:

  • Sweet And chili peppers (Capsicum spp), 
  • cyclamen flowers (Cyclamen spp)
  • poinsettia (Euphorbia pulcherrima), 
  • Transvaal daisy (Gerbera jamesonii), 
  • tropical rhizomatous herbs (Gloxinia spp), 
  • geraniums or cranesbills flowers (Geranium spp)
  • vegetable transplants
  • bedding plants

Seedlings and young plants are more vulnerable to fungus gnat infestation more so than adult plants. Larvae can seriously injure the seedlings and young growing plants. 

Can Damage The Root System

If there is an extremely high number of fungus gnat larval population present, it can even seriously injure your mature houseplants. 

As we mentioned earlier in the article, larvae prefer to feed on roots’ hairs. 

Thus, fungus gnat larvae feeding can directly damage the developing root system of your houseplants, resulting in affecting the natural ability of your houseplants to absorb water and nutrients from the soil. 

In the long run, the fungus gnats infestation will stunt the growth of your houseplants or may even kill the plant. 

Can Introduce Plant Pathogens

Fungus gnat larvae can also indirectly introduce plant pathogens to your houseplants. 

When larvae feed on your houseplants, they create multiple wounds on the plant body, creating opening points for soilborne plant pathogens. 

Furthermore, both adults and larvae are potential vectors of fungal diseases. 

Fungus gnats can transmit a number of fungal infections such as Pythium spp., Verticillium spp., Botrytis spp., Thielaviopsis basicola, and Fusarium spp from infected houseplants to unaffected houseplants. 

All these plant pathogens can cause root rot diseases and other serious fungal infections in houseplants. 

Therefore, it is necessary to prevent the growth of fungus gnats around your houseplants. 

Bottom watering Plant

How Long After Will Gnats Leave After Bottom Watering

Gnats are attracted to moist soil. So, if you can prevent your potting soil or growing medium from being moist for long periods, it can reduce the growth of gnats around your plants. 

With bottom watering, the topsoil usually stays dry, especially the 1 to 2 inches of growing medium surface where fungus gnats larvae thrive best. 

Using the bottom watering technique, one week or ten days would be enough to force gnats out of your growing medium. 

The Takeaway:

Fungus gnats can stunt or kill your young seedlings as well as mature plants. Therefore, it’s crucial to prevent the growth of these gnats around your plants, especially vulnerable seedlings. 

Bottom watering can help you greatly in preventing gnats. 

Thanks to bottom watering, your houseplants will only soak up the required amount of water against gravity. 

The topsoil of your houseplants won’t be drenched in water and prevent the growth of gnats.

With bottom watering, you don’t have to worry about overwatering or underwatering your plants as well. The plants will take whatever amount of water they want on their own.

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