Curse. This curse is a multi-stage curse that slowly takes effect the more the wearer uses it. This curse does not reset when the ring is taken off, and can only be removed with a Wish spell. Every 10 times the ring is used the curse progresses to the next stage, starting at the first stage after being used 10 times or being worn for 30 consecutive days.

Stages. These stages are cumulative and you keep all previous effects when you advance to the next stage.

Seedling
Suddenly you can no longer take the ring off, it feels as if the bones of the ring are becoming your own, and the moss begins to creep along the back of your hand. You gain advantage on rolls against magical plant-based effects that would limit your movement such as Entangle. Also, during sunny days if you spend at least 8 hours outside you only need half as much food.

Sprout
If you bleed, you notice your blood is no longer red but beginning to muddy, and you regularly find leaves and twigs in your hair. You gain the ability to move at your full movement speed in plant-based difficult terrain. However, you if you roll less than a 10 for your Initiative you start last.

Sapling
Your skin is darkening, and is rough to the touch, like bark. Your AC can no longer be less than 16, regardless of the armor you are wearing. However, you take extra damage from sources of fire. If you were immune to fire you are now resistant to fire. If you were resistant to fire, or had no resistance, you are now vulnerable to fire instead.

Spry Tree
Branches and leaves begin growing from your upper body, and your lower body is noticably thicker. If you spent at least 8 hours in the sun the previous day you sprout 1d4+1 goodberries after each long rest, as if you cast the spell Goodberry. However your base movement speed decreases by 10 feet and if you could naturally fly, you can no longer fly.

Ancient One
You are all but a plant yourself. If you stand perfectly still you are indistinguishable from a tree, and you can commune with plants around you. After standing still for 1 hour you can communicate an unlimited number of times with any plants within 30 feet, or plants who’s roots touch the roots of plants within range. This effect lasts as long as you remain still. Every long or short rest you must make a DC 12 Wisdom saving throw. On a failure you spend the rest unconscious, with your arms spread wide. At the end of the rest you must repeat the saving throw. On a success you regain consciousness. On a failure, you are petrified as a tree, though your ability to communicate with plants remains. This petrification can be ended in the typical ways such as Greater Restoration, but also with the spell Awaken.