Alistair's Absorbtion

Choose a target within range to make a constitution saving throw against your Spell Save DC. On a failure, the target takes 3d6 necrotic damage, and is still subjected to the effects of the spell. On a success, the spell fades and ends its effect. This happens of subsequent rounds for up to 3 rounds. If the target is actively destroying or disrupting the forces of nature, they have disadvantage on the save. If the target fails all 3 saves and is brought to 0 hp by this spell, their body, mind, and spirit are absorbed into the rod needed to cast this spell. Any point within the next week, you can plant the rod onto the ground and use an action to release the energy stored inside. The release acts as a level 3 Plant Growth  spell. If a charge is not used within a week of absorbing the target, the energy fades. The rod can only hold 1 charge at a time. When energy is stored in the rod, it is enveloped with green, healthy vines. When there is no energy stored in the rod, it just appears as a dark wood.