This is a losing battle I'm afraid, as every gardener will tell you. Putting down a mulch layer of grass cuttings or bark chippings will help, but never put these down unless your soil has been thoroughly soaked beforehand, especially in this hot dry weather, as it will prevent rain from penetrating down into the soil and your plants could die. Yes, bulbs should be able to grow through the bark provided the layer is not too thick, although a very thin layer will not smother strong growing persistent weeds. Slugs don't particularly like bark, so this would act as a deterrent. However, blackbirds particularly seem to like forest bark. It can provide a safe haven for insects like wood lice and they will often flick it all over your lawns and paths with their beaks in the search for a tasty snack.