You can plant it now, but only if you do it one specific way: plant it in a pot. Only Plant in a PotIf you’re eager to plant a hydrangea now, be prepared to give it a lot of water to help it get established. Watering: Newly planted hydrangeas need frequent watering to get established. Pruning: Hydrangeas need to be pruned for maximum blooms, but the timing depends on the variety. Newly planted hydrangeas need slow, deep watering so moisture reaches the entire root ball.