When you have added a Sporchid to your inventory (pink balloon-like plants that fly upwards when touched), you need to plant two of them close together and grab each one simultaneously. Sometimes one may not shoot off at the same time as the other so it may take a few attempts to get right. If the Sporchid keeps flying off without any interaction, delete it by grabbing and pressing
or plant new ones. Make sure you have no obstacles above you. The achievement should unlock in the air when you have reached 400m.
The achievement was unlocked at 0:53 (save icon) in the attached video.