Possible Clues:

• Fragrant purple flowers
• Fragrant spring blooms
• The call is for shrubs
• 'Thou art not lovelier than ___, — no' (Millay sonnet start)
• Flowering shrubs
• Large fragrant flowers of white and mauve
• Elizabeth's hiding account of shrubs
• Nosegay contents
• Flowers with the Latin name Syringa
• Eliot said they are bred in April