The Siberian elm generally needs about a gallon of water each schedule,With the potted plants, you might want to water them deeply until you see that the water is dripping at the bottom of the pot. Then, wait for the soil to dry before watering them again. You can use a water calculator or a moisture meter to determine the amount you've given to your plant in a week. Provide plenty of water, especially in the flowering period, but let the moisture evaporate afterwards to prevent root rot. If Siberian elm is planted outdoor with adequate rainfall, it may not need additional watering. When Siberian elm is young or newly planted, make sure it gets 1-2 inches of rain per week. As Siberian elm continues to grow, it can survive entirely on rainfall. Only when the weather is too hot, or when there is no rainfall at all for 2-3 weeks, then consider giving Siberian elm a full watering during the cooler moment of the day to prevent the plant from suffering from high heat damage. Additional watering will be required during persistent dry spells.