Blot the paint immediately from the plant leaves with a soft cloth or paper towel. Latex paint, especially, is easy to remove if you move quickly. Once the paint dries, though, it will be harder to work with.
Wash the plants using a gentle flow from a garden hose to remove the latex residue. Be careful not to wash away the soil or wet a recently painted surface.
Snip leaves that are coated with paint with pruning shears to remove the paint. However, if the plant is covered with paint, your best bet may be to wait until new growth emerges and the old, paint-covered leaves fall off on their own. Pruning perennials and shrubs severely, especially in mid-to-late summer may promote disease or winter injury and may also result in an unattractive plant.