AFAIK the only way to tell at what growth stage a plant/tree is at is through experience or comparing what you see with the images in the data files i.e.: crop_grapes.webp.

Can you make it easier to tell at what growth stage a plant/tree is by adding the following?

New line for a plant/tree's tooltip, under “Farming ##”.
Growth stages for plants=
1. Seedling (unwatered/unfertilized)
2. Growing Seedling (watered/fertilized)
3. “Plant name” Shoots
4. Young “Plant name” (can be harvested)
5. Mature “Plant name” (can be harvested, highest yield)
6. Hay (exclusive stage for flax/rye/barley/weeds)
7. Withered “Plant name”

Growth stages for trees=
1. Sapling (unwatered/unfertilized)
2. Growing Sapling (watered/fertilized)
3. Young “Tree name” Sapling
4. Young “Tree name”
5. Mature “Tree name” (can be harvested)
6. Picked “Tree name” (already been harvested)
8. Withered “Tree name”
9. Dead “Tree name”

Or something like it.

And if there’s still enough space, a “Growth stage 1 of 4” below it, unless it’s redundunt.

0_1527064939593_Growth stages.jpg