Mimosa trees grow quickly, attaining heights of 30 to 40 feet in five or 10 years. Although somewhat fragile, they're cold hardy only in USDA zones 6 through 10. But mimosas are fairly easy to grow and virtually care-free once established. Copious clouds of fragrant pink flowers bloom on mature trees from May through July and are followed by flat, 6-inch-long straw-colored pods. These contain from five to 10 flat, ½ inch-long, light-brown oval seeds that begin ripening in August. While many remain on the tree through December, many more are dropped generously under the tree, scattered by weather and wildlife. Many gardeners don't like this habit that's sure to give vigorous life to many new mimosa tree seedlings the next spring.
Gather a couple of heaping handfuls of mimosa seed pods when they've fallen from the tree in the fall. Cover a shallow pan with several layers of paper towels. Spread the pods in a single layer on it so that they aren't touching each other. Place it in a cool, dry spot to air at room temperature for two weeks.
Crack open the pods and remove the brown, hard and dry seeds. Seal them in a plastic bag and refrigerate in the crisper drawer until four to six weeks before the last spring frost is predicted for your area.
Fill a 4-inch pot with all-purpose potting soil to about ½ inch from the top. Plant the mimosa seed ½ inch deep and water just enough to evenly moisten the surface of the soil.
Set the pot in a warm room with plenty of bright light but out of direct sun. Keep the surface of soil evenly moist but not soggy. The mimosa tree will sprout in two to four weeks.
Plant the mimosa in a well-drained spot outside in full sun when all danger of frost has passed and the seedling is at least 4 inches tall. Keep the planting area evenly moist until late spring or early summer.
Water the established seedling only during dry spells during the summer and only enough to evenly moisten the soil. Otherwise, natural rainfall will be a sufficient water source for this plant.
Feed the mimosa seedling an all-purpose fertilizer early next spring before new growth emerges. Follow the dosage directions on the fertilizer's label.