Homestead Arcana

You'll find a few seedlings in each area of the game:

1. Canyon - corn
2. Canyon - cotton
3. Canyon - tomato
4. Canyon - cabbage
5. Canyon - lavender
6. Forest - pumpkin
7. Forest - pepper
8. Forest - rose
9. Forest - sunflower
10. Forest - soybean
11. Swamp - broom
12. Swamp - artichoke
13. Swamp - date
14. Swamp - hemp
15. Swamp - blackberry
16. City - eggplant
17. City - watermelon
18. City - gardenia
19. City - rhubarb

Plant one of each of these in your garden (you'll need to expand it via mini-dusteaters) and you'll unlock this achievement. Most of these seedlings are required for story progression anyway, but if you miss one you can always go back. If you use a Ripple Potion, seedlings are highlighted in yellow and it appears there are three of each type.