Frondescence

Frondescence (n.) The time at which each species of plants unfolds its leaves.

Frondescence (n.) The act of bursting into leaf.

I prefer to interpret the word a bit more generally to include flowers. Maybe there is a different word for the act of bursting into flower, but I do not know it.

This is one of my favorite times of the year in the garden, when plants are just coming into leaf or flower. It reminds me of one of my favorite poems, Nothing Gold Can Stay, by Robert Frost.

Nature's first green is gold,
Her hardest hue to hold.
Her early leafs a flower;
But only so an hour.
Then leaf subsides to leaf.
So Eden sank to grief,
So dawn goes down to day.
Nothing gold can stay.