There are several different plants which can be planted on Empty Flower Pots by using Seeds or Ice Flower Seeds. Most seeds cannot be directly planted in a flower pot by the player. Seeds can be traded to Rosemarie in the month of June for a random plant. Ice Flower Seeds and Megasylvan Sapling can be directly planted by the player. Most plants need to be watered, otherwise they become dry, and then wither. There are 2 initial stages (something and sprout) common to all plants, and most of them have a growing, a grown and a permanent stage, the first two being susceptible to become dry and wither if not watered properly. See the table below for all existing flowers and their stages.
Plants should be watered with a Watering Can. They can be watered every 20 hours (applies to the plant, not the player) and watering the plant gives it a chance to grow to the next development stage. When a plant grows successfully, a message appears, "Your plant has grown to the next stage!", otherwise, "You watered your plant.", and if 20 hours haven't passed yet, "Your plant doesn't need water.".
When blooming, the plant does not need daily watering. However, after 5 days without water it will wither. During this Withered Plant stage the plant can be watered to recover it to the 2nd stage. When saving a withered plant you will receive the message "You finally remembered to water your plant and it recovered.". After 2 more days without water the withered plant will die and leave an Empty Flower Pot.
A single Flower Pot (Sprout) can be found after each Floor Reset in Bounac near the NPC Onfroi here. This may be the only place to obtain them outside of the month of June.
See also: Flower Pot/Statistics
Timers such as those on flower pots do not count down if they are stored in depots (while you are away) or in your inventory (while logged off). This will allow you to preserve the flower if you cannot log in to care for them. To allow the plant to grow you must store it in a house or carry it with you while logged in.
Water flowers to their final stage 100 times to receive the Green Thumb achievement. You can reuse flower pots by saving them when they wither, which will restore them to stage 2.
Use Ice Flower Seeds on any fully developed plant to receive the Preservationist achievement. The plant will no longer wither if you do this.