Holey Pelargonium

slugs,snails? check the undersides of leaves for caterpillers

It'll be small green caterpillars, Lily, and you need to look very carefully under ALL the leaves and down the stems as well, as they're very well camouflaged! I had the same thing on one or two of mine last year. If it's slugs, you'd see the silvery trails on the leaves. Give them a spray with a systemic insecticide, but better still find the little blighters and stamp on them, then you won't kill other insects with the spray. Annie

Many thanks for your replies Kev and Annie. I had already discounted slugs or snails as slug pellets produced no results. I couldn't find any caterpillars but it was very hard to check everywhere properly so I've given it a spray as you suggest. Tomorrow I'll remove the holey leaves and hopefully I won't get any more! Thanks again.