Question
Hello Tom,
Mimosa seeds are they flat, hard come from the color part of the flower the beginning of the flower, do they resemble the leaves when they dry? Please give me what you have be specific about what the seed looks like. Any picture that you have or where I can see the seed only?
THanks
Doug Recher Long Island ny

Answer
Hi Doug,
Thanx for your question.  It just so happens I have a mimosa tree (Albizia julibrissin)growing in my backyard.  They are hardy to Zone 6 and some parts of Zone 5b.  The plant usually doesn't put out leaves in the north until May and then a profusion of silky pinkish or whitish blooms cover the canopy-like tree in July and August.  After the tree flowers it forms a seed pod like a locust because the plant is a legume (related to peas and beans).  The seed pod is brown and almost flat and eventually turns a yellowish/brownish color.  In the pod are about 10 seeds.  The seeds  are flatish, brown, hard, but they germinate readily like bean and pea seeds.

Mimosa (silk tree) seed pod picture
http://images.harc.edu/Sites/GalvBayInvasives/Species/Photos/ALJU_0016012.jpg
Mimosa (silk tree) seeds
http://upload.wikimedia.org/wikipedia/commons/7/70/Albizia_julibrissin_seeds.jpg

Start the seeds in the spring a few weeks before the last frost and plant about 1/2 inch deep.  Keep moist but not soggy.  Germination occurs in 10-20 days.  Plant in separate pots when about 3 inches tall.  Put outdoors after the last frost in the shade for 10 days and then in full sun in the desired location.  

Some states consider this tree invasive and its cultivation may be banned or restricted.  Check with your local County Extension office.  If you need contact information for your local extension office, let me know.  I hope this helps.
Tom