As with nearly all of these Eternal Achievements - you can set up a deck to target this achievement and play Gauntlet mode. In Gauntlet mode - you can set up a scenario where you prevent the AI from doing anything meaningful by setting up a defensive wall of units that will not be killed if the AI units attack. This creates a stalemate that will let you continue to draw cards and set up the necessary requirements.
This specific achievement relates to using the Hermit Gardener card to trigger Little Seeds into transforming. This can be done with any Little Seed card, but the easiest is to use two Hermit Gardeners - play the first one and it will spawn two Little Seeds - wait two/three turns and play the second one (the counter on the Little Seeds must be at 3 or higher).
Achievement will unlock at the end of the battle.
NOTE: As of 08 JAN 2021 - there is a bug with Milestones (in game achievements) and Xbox achievements. The Milestones for In Bloom / Ascension / Brilliance are mixed up, so while the in game milestone pops up correctly - you will be awarded the following achievements Brilliance / In Bloom / Ascension.
TLDR: This achievement will pop when the Milestone "Ascension" pops.