Your garden may be too small for a hedgehog ... most gardens are ... but if gardens are linked up (as the ones in our neighbourhood are) your local hedgehogs can roam around all the gardens, meeting each other and making hedgehog families, and while they're doing that they're eating your garden pests.
According to the Guardian pure coffee grounds badly inhibit plant growth. So, if using for slugs, put them on something, so it doesn't get into the soil in high concentrations.
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https://www.hedgehogstreet.org/help-hedgehogs/link-your-garden/
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
Apparently Newcastle University found garlic oil kills slug eggs too, so that is worth trying.
Anyone know the cheapest source of caffein? There is a high caffein berry from South America used in energy drinks but don't know what it is called.