Buy mimosa at your neighborhood garden store. However, if you decide to start from scratch, several weeks before you intend to plant them, place the seeds in warm water overnight, and then throw away those seeds that don't enlarge. Place the remainder in potting soil and they will grow large enough to plant. If you'd prefer using cuttings, cut seedlings about 4-inches long from existing plants and dip them in rooting hormone that you can also get at your garden store. Place each one in flats with potting soil and you should begin seeing new growth by the time you intend to plant them. Cuttings will be larger than seedlings; so when they are planted, they will spread more quickly than seedlings.
Make sure you have enough plants or cuttings for the area you wish to plant. As a rule of thumb, you will need about 225 for every 10-foot-by-10-foot area.
Pick an area that gets lots of sun and work whatever compost you have into the soil. You do not have to dig too far into the soil because mimosa tends to grow well as long as there is direct sun.
Place strings about 8-inches apart, then dig a small hole about every 8 inches along each string. Into each hole you should place one of the cuttings or plants.
Water abundantly once you have planted the area because the new plants or cuttings are very delicate. You should keep it watered, for awhile at least, but first you'll need the ground to dry thoroughly. Fortunately, mimosa doesn't need fertilizer and it will grow hardily if you plant it in a sunny area.