About how old is a 10′ tall eastern redbud tree with 1.5″ caliper in a 20-gal nursery tub?
Just wondering how many years until it will bloom.
Certified GKH Gardening Expert
Their flowering habit is a bit unpredictable when it comes to age. Sometimes they only take a few years to flower, and sometimes they take many years to flower. It is also very difficult to guess a trees age (especially in container) without killing it.
With that being said, and knowing that it is in container, my guess is that it doesn't have enough nutrients. I would feed this once per year with an all purpose. They aren't heavy feeders, but they can lose nutrients in container by rain washout.
You may also want to take it out of container, and cut out the thickest roots, leaving the smaller feeding roots. They don't need stabilizing roots in container, since these are to keep it upright in the open ground.This will be done, either, right after flowering, or during dormancy.
Make sure that you replant with good topsoil mixed with compost, or mixed with potting soil.
This article will help you with the care of Redbuds: https://www.gardeningknowhow.com/ornamental/trees/redbud/caring-for-redbud-trees.htm