"Now that lilacs are in bloom..."

Perhaps the most famous poem about lilacs is Walt Whitman's When Lilacs Last in the Dooryard Bloom'd. It was written as an elegy for Abraham Lincoln, right after he was assassinated in 1865. Once upon a time, every schoolchild read it, or (heaven forbid) had to memorize all sixteen stanzas.

An old and beloved shrub on farms, ranches and in city gardens, lilacs are mentioned in many works of literature.

But my favorite "lilac lines" are from a T.S. Eliot poem called The Portrait of a Lady. This poem has a story of sorts. A young man is visiting an upper class English lady of a certain age, with whom he's had a relationship. He tells her he's leaving to take an extended trip abroad. She listens and puts on a brave face, but she has a few sharp words about "youth."
Here's the lilac stanza:

Now that lilacs are in bloom
She has a bowl of lilacs in her room
And twists one in her fingers while she talks.

'Ah, my friend, you do not know, you do not know
What life is, you who hold it in your hands';
(Slowly twisting the lilac stalks)
'You let it flow from you, you let it flow,
And youth is cruel, and has no remorse
And smiles at situations it cannot see.'

I smile, of course, And go on drinking tea.

from,
Portrait of a Lady
T.S. Eliot