To craft the powder, you will need:
1 Prismatic Shard
10 Solar Essence
10 Void Essence
To use, just select it in your toolbar and click on something that needs growing (crops, trees, fruit trees, tea bushes, farm animals, or children).
Not yet tested on children. Please don't sprinkle growth powder on your children in real life.
Technical
Requires SMAPI and JSON Assets, uses Harmony.
Compatible with Mod Updater for automatic updates.
Code is at https://github.com/aedenthorn/StardewValleyMods.
If you want to complain or ask for help or help me test my mods, you can visit my Discord server.
A list of all my mods for Stardew Valley is available at https://www.nexusmods.com/stardewvalley/articles/895.