coffee grounds and mosquitoes

Do Coffee Grounds and Mosquitoes Get Along?

I’m a big coffee drinker and fan of really great coffee so I’m always on the lookout for a use for coffee grounds. For example, I know worms treat them like candy and prefer them to most other foods (I have worm farms).

And I know that caffeine is a great slug killer but coffee grounds don’t contain enough left-over caffeine to really do anything to slugs except “maybe” deter them a bit. (it’s not the grounds the slugs don’t like, it’s the caffeine contrary to published Net blogs.)

Mix This Up

What I didn’t know was that coffee grounds are pretty potent mosquito larva killers.

Four heaping tablespoons or big soup spoons of coffee grounds – when mixed with 250 ml of water offer 100% control of larva. Kills ’em dead!

From a practical point of view – making sure this amount of used coffee grounds in water to get the right concentration is a standing pool of water is going to take a ton of grounds so it might not be practical there.

It may work as a spray if you can isolate a section of long grass where mosquito larva are living.

Dusting The Grounds

Where it is going to be practical is in the garden itself. So when you have leafy plants (Southern gardeners take note!) where water sits in the leaf axils (where the leaf hits the stem) and mosquitoes breed there, dusting plants with coffee grounds will put enough grounds into the axils to control breeding mosquitoes and eliminate one source of these bloodsuckers.

How To Make It More Potent

I also note the longer the caffeine mix sits around – the more potent it becomes so don’t wash it out.

Day-old caffeine solutions took 20 days to kill 100% of the larva while a 25 day-old solution killed 100% in 1 day.


So you can feed them to the worms in compost bins or dust plants in the garden.

You can read other articles about compost here

7 thoughts on “Do Coffee Grounds and Mosquitoes Get Along?”

  1. Very interesting…. as a big coffee drinker …. i have been composting the grounds for the high Nitrate qualities or so i read ….. Great to have another usage….. keep up the good articles…. so learner, but a fast reader.
    I will test this new bug soup starting this week…. got to love the organic side of this article…
    Bill

  2. So how many pounds of grounds would I need for a 45 gallon rain barrel? At 4 Tb per cup….anybody got a calculator?
    The cover I have is not doing the trick so I reckon hanging them in a net bag in the barrel might help.

  3. LOL! Jane – 4 tablespoons is roughly equivalent to .002 604 166 666 7 gallons.
    or 45 gallons contains 69 119.999 999 tablespoons.
    How are we doing from there?
    http://www.onlineconversion.com/cooking_volume.htm is one such conversion site where you can convert darn near anything to anything
    For a rain barrel – try putting a small amount of cooking oil into the barrel. Just enough to put a film on the surface. The oil spread on the surface preventing the larva from breathing (they come to the surface and stick a “nozzle” across the air-water divide to breathe at one point in their development) works like a charm.

  4. For those who need more coffee grounds, just check with a local coffee shop. I put 2 – five gallon buckets at our local shop. I pick those up and put in new/clean buckets every 3-4 days, which yields 3-4 buckets full per week. The buckets make it easy to handle both in the shop and in the garden. I do screen out the filters as they do not decompose very fast.
    Does the espresso yield a lot more caffeine?
    Have not had a mosquito problem here at all the last few years and now I know why!
    The coffee grounds also acidify soils for plants who need that.

  5. Doug: Thanks for the information. Since I am not good at math I will try the oil then.
    Moni: Regarding caffeine sources check out this Wikipedia article. en.wikipedia.org/wiki/Caffeine –
    Here is an excerpt from a much lengthier article “One of the world’s primary sources of caffeine is the coffee “bean” (which is the seed of the coffee plant), from which coffee is brewed. Caffeine content in coffee varies widely depending on the type of coffee bean and the method of preparation used;[18] even beans within a given bush can show variations in concentration. In general, one serving of coffee ranges from 40 milligrams, for a single shot (30 milliliters) of arabica-variety espresso, to about 100 milligrams for a cup (120 milliliters) of drip coffee. In general, dark-roast coffee has less caffeine than lighter roasts because the roasting process reduces the bean’s caffeine content.[19][20] Arabica coffee normally contains less caffeine than the robusta variety.[18] Coffee also contains trace amounts of theophylline, but no theobromine.
    Tea is another common source of caffeine. Although tea contains more caffeine than coffee (by dry weight), a typical serving contains much less, as tea is normally brewed much weaker. Besides strength of the brew, growing conditions, processing techniques- and other variables also affect caffeine content. Certain types of tea may contain somewhat more caffeine than other teas. Tea contains small amounts of theobromine and slightly higher levels of theophylline than coffee. Preparation and many other factors have a significant impact on tea, and color is a very poor indicator of caffeine content.[21] Teas like the pale Japanese green tea gyokuro, for example, contain far more caffeine than much darker teas like lapsang souchong, which has very little
    J

  6. Jane – thanks for passing this along – great info for those of us who drink coffee 🙂

  7. Doug – I, like a lot of other people, thought that if it was very dark coffee it was full of caffeine, until some coffee purveyors told me different.
    Info not so great for the mosquito larva though eh Doug? It probably has them quaking in their tiny boots about now.

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