To use coffee grounds is a much discussed method against snails in the garden.
Here it will be tested.
Now coffee has to show what it really can do against slugs and snails.
Does coffee help with snails?
It is often reported that coffee grounds on the beds and around the plants would help to deter slugs and snails.
But the question is if this really works or if it is part of a fairy tale, opinions vary widely.
There is no clear answer yet.
Some gardeners are convinced that for them coffee grounds in vegetable and flower beds are a valuable help and protection method.
But others report how the slugs damage the plants despite of the coffee.
There are reports on scientific results which should confirm the effect of caffeine and coffee, but unfortunately exact sources are missing.
How should coffee grounds work?
It is believed that caffeine is toxic to slugs in large doses and that it would slow them down in smaller doses.
In some sources it is noted that the smell of coffee alone could deter snails.
In addition, others state that ingredients in the coffee grounds would stimulate the mucus production of the snail, which in turn could deter them from crawling over it.
How should coffee grounds be applied in the garden?
Usually dried coffee grounds are used as wall.
They are distributed on endangered beds or scattered directly around endangered plants in the form of a wide protective ring.
In addition, some supporters of coffee against slugs advise spraying the plants with coffee concentrate would protect them from slugs and snails.
Coffee grounds the test
It was time for me to look into it and perform my own test.
Therefore I dried a lot of coffee grounds, then I spread them in a wide semicircle and placed about 20 different slugs and snails in its center.
What happened then, is shown in the following time lapse recording:
Video: Coffee against snails in the test
The recording shows how some snails, despite the dust-dry coffee, easily crawl over it.
Some are reluctant but others cross the coffee without hesitation.
It can be observed that some slugs immediately back away or turn around after contacting the coffee.
However, it can not be seen that alone the smell would deter the snails. On the other hand it seems to attract them.
Also the claim caffeine would make the slugs sluggish, seems not to be true.
While it can be witnessed that some tiny slugs are slowing down a bit, that is probably because the coffee grounds were super dry. Other larger slugs did not slow down at all.
So the experiment has shown that coffee is by no means a universal remedy.
Although it works slightly as a deterrent, coffee grounds are not effective enough to protect vulnerable plants.
Most of the slugs in this experiment were very young and small.
It can be expected that the protective coffee wall will not be an obstacle for them once they are grown up.
Conclusion: Advantages & Disadvantages
The experiment has shown that coffee grounds have a little effect on some slugs and snails, but clearly it will not be enough to protect the snails’ favorite plants.
Especially in a large garden with many snails it will not be sufficient to put out a daily portion of coffee to repel all snails.
This would be just too good to be true.
In addition, it is expected that rain will annihilate the protective effect, which is the biggest shortcoming of this method.
However, to put coffee does no harm to the garden, on the contrary the coffee feeds earthworms and the plants also like the minerals contained in the grounds.
Thus in the end it makes sense to distribute the coffee grounds in the garden, instead of disposing it on the compost or in the trash.
If anyone has experience with coffee as a spray, I would be very grateful for all comments on this topic and especially some evidence for or against its effectiveness.
Effective Slug Control Alternatives
There are some other slug control methods that might interest you:
slug fences (soon)