Bob’s new vegetable patch at the bottom of the garden is being sabotaged by slugs. They emerge at night to munch on his tender lettuces and fledgling bean plants. We know the slugs dislike crawling over certain things, so for a while we collected our coffee grounds and spread them around the plants, but rain kept washing them away. We tried gravel and expensive bands of copper, to little effect. Sometimes Bob goes out at night with a torch and a bucket of water to collect slugs, but he doesn’t feel like doing that very often. (When I first typed that sentence, I wrote ‘Bob goes out at night to collect slugs with a torch and a bucket of water’, but that conjured up an awful vision of torch-wielding aquiferous slugs.)
Now he’s moved the campaign into a new phase by building a little wooden barrier around the vegetable patch, and affixing sandpaper to the outside of the barrier. So far this prickly wall has defeated the slugs.
We’ve been discussing whether it’s enough to have a barrier above ground level. Slugs can also burrow, so it seems likely that on meeting the barrier they may simply dive (if that is the word) under it and rise up triumphant among the lettuces. Should the sandpaper barrier be extended downwards, under the ground? What depth would deter them, and whom else would it deter?