Slugs love hostas, and it is rare that a garden has one without the other. Hostas are so persistently targeted by slugs, that some varieties of hosta have developed a mild resistance to the pest. But this is rarely enough to ward off an attack. And eventually, almost every hosta grower will notice small round slug-holes in the hosta’s leaves or slime trails in the garden. Unfortunately, it can be quite difficult to permanently control slugs in hosta gardens. To keep their population down, keep a number of control methods going in your garden as long as your hostas are around.
Spread mulch around your hosta beds. Cedar, oak bark or gravel chips will irritate the slug's skin and dehydrate them. The best time to spread mulch is once the soil has temperature has reached above 75 degrees Fahrenheit.
Spread diatomaceous earth over the ground. Diatomaceous earth is made up of the sharp, fossilized remains of diatoms. When the slugs slide over it, it will pierce their skin and eventually dehydrate them. A light dusting of the powder is sufficient for control. But it will have to be replaced whenever it rains or you water the plant.
Sprinkle Epsom salt over the soil. Salt dehydrates slugs, and the magnesium that it leaches into the soil will deepen your hostas' color, thicken their petals and strengthen their roots.
Spread slug pellets containing iron phosphate or metaldehyde over the soil. However, be aware that some of these pellets can be toxic to other garden birds or animals that may ingest them.
Leave a few layers of wet newspaper over the ground around your hostas overnight. The slugs will take cover under it. Early the next morning, pick up all the slugs and drop them in a bucket that contains a 20 percent solution of ammonia. Chopsticks are a great tool for this if you do not want to touch them. Sprinkling salt on the slugs will also kill them.