Ageratum (Ageratum houstonianum), a popular annual and one of the few true blue flowers, is easy to grow from seed.

How to Plant Ageratum. Ageratum plants may be started from seed when the soil has warmed outside. Cover seeds lightly, as seeds of ageratum plants need sunlight to germinate. For an early start to blooms of the ageratum flower, start seeds indoors eight to 10 weeks before planting in the spring garden.

Ageratum, also known as floss flower, is an easy-to-grow summer annual with fluffy purple flowers. It is one of those special plants that will re-seed itself without becoming particularly invasive, making it a great choice for cottage gardens.

To gather ageratum seeds, pick a dried blossom and slowly roll it between thumb and forefinger over a sheet of paper. For easier separation of the tiny petals and the small, slate-gray rectangular seeds, blow lightly on the pile. This will scatter most of the petals and leave the heavier seeds.. . . . .364011236350!]0000000000000009783314147658!]