The Patch 3.4 Notes (Preliminary) have been released. It includes a few additions and updates to gardening:
New items can be grown via gardening.
New soil has been added (Potting Soil). While this new soil is inexpensive, it grants no bonuses to harvesting. It can be purchased from the Material Suppliers.
The time required to harvest plants from the elemental seeds has been reduced (Icelight, Firelight, etc)