You might want to put a garden hose at the plant base to ensure that you're promoting excellent root development. Avoid directly spraying the leaves, and know that the leaves will require more watering if they are outdoors and facing direct sunlight. You can also use bubblers that you can put on to each plant to moisten the roots. Also, use soaker hoses that can cover the entire garden or bed when adding or removing plants to push the roots deeply. Drain any excess water and wait for the soil to dry before watering. Water at ground level to prevent diseases. On a sunny day, you might want to spray the entire bush with water. Whether potted or in-ground, please remember Siberian elm prefers deep watering over light sprinkling.