I've had several e-mails from friends of this website mentioning using coffee to deter slugs.

The Today programme on Radio 4 reported research in Hawaii suggesting that spraying caffeine on plants was much more effective at killing slugs than metaldehyde (the active ingredient in many slug pellets).   Since then, I've seen multiple testimonies to its efficacy; ideas of using coffee and coffee grounds are all over the internet now.   An "organic" cure to our slug problems?

But I have too many niggles, doubts and questions that bother me - so I'm not going to get excited yet, and I'm not going to use it either!

• If the caffeine mixture (at a concentration of 1 or 2%, apparently) is so effective against slugs, what does it do to any other organisms --- earthworms? beetles? fungi? etc?
• And what effect does the caffeine have on growing plants?   I don't know.
• Interesting - it seems that the slugs have to eat the plant to get the caffeine.   But I want to eat my cabbages!

• The research involved pure caffeine mixed (I think) with soaps.   Not quite the same thing as coffee.
• What about using coffee?   A normal mug of instant coffee only contains about 0.05% caffeine.   Hmmm, that means putting 20-40 teaspoonfuls of coffee per mug of water!!!   With real coffee, about half that.
• Caffeine is accepted for human consumption - but at that sort of concentration?   I don't believe it.
• Apparently, concentrations as low as 0.1% can act as a deterrent.   But that's still a lot of coffee, 1 teaspoonful of real coffee per mug of water, or 2 of instant.   Firstly, I can think of better things to do with real coffee; and secondly, I still don't know what it does to other beneficial creatures and organisms.

• What about the acidity of coffee?   I believe normal black coffee has a pH of between 4.5 and 5.5, so what effect does this have on my plants or my soil?
• How persistent is the caffeine in the soil - I don't know.

• I've seen claims made for using coffee grounds - but since the caffeine has already been extracted into the brew, I suspect there's some other process going on; perhaps it's as simple as improving the condition and structure of the soil?

Funny thing this writing business - I started by simply wanting to list my doubts and niggles.   But I've surprised myself by argued myself into categorically deciding NOT to use coffee, and NOT to be distracted by the "noise".

I'll stick to drinking my coffee; it'll sustain me as I control my slugs without really having to think about it.