Seed Cache contains seeds which can be planted in the Sacred Grove.
Clicking a Seed Cache, it advances a growth cycle and drops Tier 1 seeds.
In the Harvest league, each zone will contain a seed cache.
If entered from a zone, the Sacred Grove will be part of the instance you entered from, which means map modifiers and such will apply within the Grove as well.
Entering the Sacred Grove from a different zone or from the waypoint will create a new instance of the Sacred Grove, so do not enter the Grove from anywhere other than how you first spawned it, or you will lose any unfinished harvests.
You can put a Seed Stockpile in your hideout.