Tablet "Onion"

A Tablet “Onion” marks the row of five garden beds beside it for onions. A zombie gardener from a Gardener Stand plants 4 Onion seeds in an empty marked bed and harvests the onions when they are ripe; the seeds must be in an open chest in the garden. The tablet is free and comes with Zombie Gardening (60 green, 20 blue). It goes on one of the garden’s tablet spots: two at first, four after Garden Upgrade I, six after Garden Upgrade II.

Notes

Onion seeds come in three grades, and the gardener takes the first grade it finds four of. Unconfirmed: probably the lowest you have. Keep only the grade you want in the garden’s chests.
By hand, onions need Farming mastery 10 to 14 to plant; a gardener plants them regardless, since planting is a graded craft.
Onions go into the factory’s second preserves crate, on a Kitchen II with its Sealing Machine.