Q.Crabapple hedge
We have planted several crabapple trees for a hedge approx 4 years ago and they haven’t given any flowers or fruit yet. How long does it normally take and can I do something to improve the situation?
Lack of flowering or fruit can be due to inadequate sunlight, warm winters,
drought stress, planting errors, tree age and disease.
Your trees are still young and actually produce a chemical that stops them from blooming while the roots develop. In some cultivators this can last 10 years, before the tree begins to produce flowers.
https://www.gardeningknowhow.com/ornamental/trees/crabapple/flowering-crabapple-trees.htm