Many of us have already experienced the effect of caffeine on the human organism. Snails also react to the neurotoxin. Can this effect be used, does coffee grounds help against slugs in the garden?
Coffee grounds, made up of ground coffee beans, are a by-product of making coffee. It contains around 2% nitrogen, 0.8% potassium and 0.4% phosphorus, which are important plant nutrients, as well as tannic acids, antioxidants and caffeine. Therefore, it has certainly already been encountered by one or the other as a fertilizer. In addition, coffee grounds in the ground attract earthworms, which loosen the soil. Ants and cats, on the other hand, are kept away from the bed. You will now find out below whether this also applies to snails.
Does coffee grounds help against snails?
First of all, a distinction should be made between different applications. On the one hand you can sprinkle coffee grounds against snails, on the other hand you can spray plants with cold coffee or coffee grounds extracts. When used correctly, coffee and coffee grounds can help against snails - but they also have side effects. We will address these in the next chapter. The caffeine in coffee literally gets on the snails' nerves, after all it's a neurotoxin.
Dry coffee grounds against snails
As pure coffee grounds, it is only a deterrent and does not work completely reliably, because the concentration of caffeine in the coffee grounds is not high enough. If slugs have a particularly large appetite, the coffee grounds can hardly stop them.
Cold coffee or coffee extracts against snails
In the course of research at the University of Nebraska, substrate or leaves of plants were sprayed with caffeine solutions of various strengths. It was found that snails are deterred from a caffeine content of more than 0.1% and sometimes even killed from 1%. The caffeine content varies in different coffee beans. Arabica coffee has a content of 0.8 to 1.4%, Robusta coffeeone from 1.7 to 4%. However, brewed coffee has a lower caffeine content of around 0.06 to 0.1%. So if you want to produce a more concentrated caffeine solution like in the experiment mentioned above, you have to brew a very strong coffee. However, the high concentration of caffeine can also harm other creatures in the garden, as you will learn below.
Tip: What you should know about both methods: Caffeine, which provides the effect, is water soluble. That means it washes away when it rains.
How does coffee work against snails?
Physiological studies of mollusc neurons suggest that caffeine releases calcium from their internal stores, thereby prolonging action potential duration. The action potential is used to transmit stimuli. If it is elevated for longer than usual, in addition to increased oxygen and energy consumption, there are other reactions in the body that can ultimately lead to collapse. However, a slug crawling over soil mixed with coffee grounds is unlikely to ingest enough caffeine to die.
Other studies indicate that certain ingredients in coffee grounds stimulate mucus production and deter the snails, since they would fear increased water loss.
It is also believed that the smell of coffee alone deters the snails, as they have a sensitive sense of smell and they don't particularly like the smell of coffee.
Important: Highly concentrated caffeine has an undirected harmful effect on most living beings.
On the one hand, the nerve toxin caffeine also has a deadly effect on beneficial organisms such as snails, earthworms and insects or at least intimidating. On the other hand, according to a study, high concentrations can damage the plant.
Use coffee grounds against snails in the garden
In the garden, dried coffee grounds are used against snails. Coffee powder can also be used, it even has a higher caffeine content. However, it is questionable whether an expensive and resource-intensive stimulant like coffee should really be scattered in the garden.
We recommend spreading coffee grounds around susceptible plants. The intense smell inhibits the snails from crossing such a wide barrier. The ring should only be renewed once during the year in order tonot to damage soil life with caffeine.
Undiluted cold coffee can be poured on the soil near the plants. Most plants can also tolerate being sprayed directly with cold coffee. However, flowering plants should be excluded, since the coffee deters both snails and pollinators.
We recommend keeping an eye on the weather so that the coffee doesn't get washed away by the rain. Therefore, do not spray the plants if a shower is already falling on them afterwards. Since the application is still relatively new and unexplored, there are unfortunately no precise statements as to which plants could be affected by leaf damage from coffee and in what form. The motto here is therefore: try it yourself.
Conclusion: Unfortunately, coffee grounds do not work reliably against snails and can affect beneficial insects in your garden. If the snail population in the garden is too high, this is not a solution.
You can find out how to effectively prevent and get rid of these pests in our article on combating snails. There you will find numerous tips, such as the use of slug pellets.
If you don't drink coffee, don't want to harm beneficial insects with caffeine or have more than just one or two snails in your bed, you'll of course look around for alternatives and will find what you're looking for at snail grain. This remedy is effective when it comes to eliminating snails in the garden. Since conventional grain made from metaldehyde can cause harm to children, mammals and other living beings, we at Plantura offer a less dangerous, beneficial alternative. Our Plantura organic slug pellets consist of iron-III-phosphate and ensure that the slugs retreat to their hiding places after consumption without mucus formation and die there. You can find out how to use it correctly in our article on slug pellets.
In addition to various remedies that are available against snails, you can also rely on the support of certain plants. You can find out what these are in our articles on slug-resistant plants and plants against slugs.