Long ago, I discovered the value of french drains in preventing standing water in a yard. This is especially true when the lawn has a significant amount of clay in the soil.
As great as french drains are for moving water, the water basins that serve as inlets are perfect breeding grounds for mosquitos. They are dark, wet, and usually undisturbed except during a rainfall.
There are three essential strategies for getting rid of mosquitoes in yard drains:
- Prevent entry with a screen or by removing the inlet drain
- Eliminate the standing water in the catch basin
- Prevent mosquito eggs from maturing with mosquito larvae specific toxin
Let’s have a look at the advantages and disadvantages of each of these approaches so that you can determine the best approach for your yard.
Prevent Mosquitoes From Entering A Yard Drain
The most obvious approach to getting rid of mosquitoes in yard drains is to stop them from getting into it in the first place. Unfortunately, this is not as simple as is sounds.
Mosquitoes are very small and can find their way in if a desirable habitat exists. Still, any effort to prevent entry is a smart place to start. I’ve seen a couple of approaches to this that are effective.
Apply A Screen To Your Catch Basin
The first way to stop mosquitoes from entering your yard drain is to use plain old window screen or very permeable landscape fabric over the catch basin. This will still allow water to flow through but will help prevent mosquitoes from getting in.
The process is pretty simple. Remove the catch basin’s cover and place the screen or fabric over the opening. Replace the catch basin cover and secure in place.
Next, using a razor or scissors, carefully cut the screen or fabric so that its edges are flush with the catch basin cover.
This process is effective but it has inherent issues. First, the purpose of a catch basin is not only to serve as a water inlet but to catch leaves and other debris and keep them out of the drainage system. The basin ensures that water flows freely without clogging the drains.
By adding a screen or fabric to your catch basin, you may risk stopping up the inlet. Debris will get caught on the surface and can pile up, reducing water flow.
Cover The Catch Basin Completely
The second approach to prevent the entry of mosquitoes into your french drain is to completely cover the inlet. This can be done by filling the catch basin with large stones.
The stones serve as an aggregate that still allows water to flow through. A square of grass sod is then placed directly over the catch basin so that the turf is flush with the surrounding soil.
Over time, the grass interweaves and an indistinguishable drainages system is established. While this is clearly the “cleanest” look and should significantly prevent mosquito growth in the drain, it still prevents debris from passing into the basin.
That’s not necessarily a bad thing since it is effectively keeping debris out of the drains but it will also impede the flow of water into the drain. If you have an area that requires rapid movement of water to prevent flooding, this may not be your best solution.
Eliminate Standing Water In The Catch Basin
We know that standing water is the culprit of our mosquito growth. Why not simply eliminate it from the equation?
By drilling holes in the bottom of the catch basin, you can create a path for standing water to leach into the ground. This will reduce the amount of standing water in the catch basin.
This is good practice in any french drain installation and it’s peculiar that most basin’s don’t come with these leaching holes pre-drilled.
One problem that you may have is if the basin is in clay soil it can have difficulty leaching excess water. Additionally, over time, debris can clog the holes, also preventing leaching.
Kill The Mosquito Lavea Before It Matures
The final approach to getting rid of mosquitoes in yard drains is by preventing them from breeding. Mosquitoes lay their eggs on hard surfaces near standing water (source). The water is essential to the growth and survival of the larvae.
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A homegrown approach to this is adding dish soap to the catch basin. The soap creates a film in the standing water that prevents the larvae from being able to breathe (source).
The only problem I foresee is having to add more dish soap after each rainfall.
A longer-term strategy is to apply a slow-release product. Summit Chemical Company produces a product called Mosquito Dunks. These are non-toxic to other wildlife but kills mosquito larvae. One application lasts up to 30 days. All you do is drop them into the standing water in your catch basin each month.
The Bacterium That Kills Mosquito Larvae
What’s really cool about the Mosquito Dunk product is that it isn’t using some highly dangerous chemical. Its key ingredient is Bti which is a bacterium that is found naturally in soil.
Bti is deadly to mosquito larvae, black flies, and fungus gnats but harmless to humans other animals as explained by this article from the Environmental Protection Agency. It can be used in and around natural bodies of water as it does not pose harm to aquatic animals (source). It’s even labeled for organic gardening by the EPA.
You can download the Safety Data Sheet for Mosquito Dunks from the manufacturer’s website by clicking here.
I purchased some of these Mosquito Dunks recently. I was a little concerned that with heavy rainfall the treatment discs may be pushed out of the catch basin into the french drain system.
But I figured out a handy way to prevent this with a pair of my wife’s old pantyhose.
Cut about 6 inches of pantyhose legging. Tie a knot in one end. Insert the Mosquito Dunk into the pantyhose along with a large rock or two. Tie a knot on this end but not so tight that you can’t loosen it later.
This ensures that the treatment disc doesn’t float away.
Pretty nifty, right? 🙂
What’s The Best Way To Keep Mosquitoes Out Of A Yard Drain?
Each of these solutions offers potential benefits and downfalls. Which one you choose will likely depend on your particular situation. I have been very pleased with the results of the Mosquito Dunks but I did have to add a reminder to my phone to replace them each month.
I’m considering filling the basins up with rock and covering with grass sod as explained earlier. I believe that will be the best longterm solution in my case, at least with one of the basins.
But the primary catch basin moves a lot of water from my front yard so I’m not too keen on covering it up. For that one, I’ll likely stick with the treatment discs.
If you have no concerns about debris potentially clogging the inlet, using a screen or fabric will likely do the trick. But if that’s a concern for you then applying dish soap or purchasing Mosquito Dunks may be your best bet. Mosquito Dunks are available on Amazon. Click here for the latest pricing.
Having mosquitoes breeding in your yard can ruin your outdoor experience. Remember that standing water is a prime breeding location and be mindful of items left in the yard that collect and hold water.
When it comes to your french drain system, take the time to do at least one of the steps outlined in this article to prevent mosquitoes from breeding in your yard drain.
And don’t stop there. Look for other areas prone to mosquitoes and take steps to address those as well.