Hi Chantenay !
Hugh appears to have gone fishing ...( again ! ) ;D
But while we await his return, maybe this will help ? Happen to have saved it as a reminder !
Hope it helps ! :)
The coffee I used was not intended to kill the slugs - a 2% caffeine solution would have been required for that - but was used as a deterrent at normal drinking strength of 50 gms per 2 gals of water, and was the cheapest I could find (Aldi at 37p per 100 gms)
Without setting out the full details of the tests, the conclusions I finally reached were:-
1. The coffee was an excellent deterrent, and, once treated (thoroughly drenched) the soil remained cleared of slugs for up to 2 months unless there was excessive rain
2. Coffee applied to growing plants, especially young carrot seedlings could cause chlorosis and retard growth in some cases
3. Coffee applied to mature carrots in September did not adversely affect the plants.
4. The most beneficial way to use coffee is to drench the bed some two or three weeks before sowing to clear slugs out, and then to re-apply around the edges of the bed only at intervals throughout the season to maintain a barrier. I always overwinter my maincropcarrots in the ground, so once they had matured in September they were drenched, and this was repeated in November to keep the crop clean - there were no ill effects on the carrots.
The coffee was also used around (not actually on) Hostas at a radius of about 6inches from the plant stems -once in late spring and again in midsummer. Not one plant was attacked and the plants showed no ill effects.
As to the matter of the pH levels, 50gms of coffee used in this manner will have no more effect than a bucket of garden compost dug in over the same area.
