Blossom, bloom, flower, blow are comparable as verbs when meaning to become florescent and as nouns when meaning the period or state of florescence or (except for blow) meaning the florescent part itself.
Blossom may be used of a plant that reaches the condition of florescence, but typically it applies to trees, shrubs, and herbaceous plants (and to their florescent parts) that normally proceed to bear what is ordinarily (not technically) called a fruit.
Bloom, though sometimes employed interchangeably with blossom, is typically used of such herbaceous plants, shrubs, or trees (or their florescent parts) as have reached the height of their beauty during the period of florescence.
Flower in technical use as a noun refers to the part of a seed plant which normally bears reproductive organs; in popular use it is usually restricted to such part when its gross structure is showy and conspicuously colored or white. (see also: Yellow trumpet vs Yellow trumpet flower and Tudor flower vs Tudor rose)
Fragrance, freshness, shortness of life or of beauty are the implications in the popular use of the noun and the verb that distinguishes flower from bloom chiefly but also from blossom; also flower is often thought of as apart from the plant where it has grown.
Blow, in this sense, has an archaic or poetic flavor except in the combination full-blown. Usually it suggests a bursting into flower or bloom and often, especially in the noun, connotes a great display of blooms.
All of these words have extended use. Blossom usually suggests something analogous to a natural blossom (as in freshness or rich development).
Bloom usually suggests a time or period of perfection, vigor, or beauty.
Flower implies the choicest part, specimen, or product of something or its coming into being.
Blow, by far the least frequent of these terms in such use, implies a bursting into beauty or perfection.