Miniature zinnias display showy summer blooms that last well into fall. The fast-growing plants have single, double or semi-double flowers in a wide range of colors. Dwarf cultivars of the most commonly grown zinnia (Zinnia elegans) reach from 10 to 15 inches tall. Narrow leaf zinnia (Zinnia augustifolia) grows to only 18 inches tall and can overwinter in U.S. Department of Agriculture plant hardiness zones 9 through 11. Modern miniature zinnia varieties come from a wildflower native to Mexico and the Southwest, but grow well in all areas as annuals.
Remove weeds and spread a 3-inch layer of compost on the bed and till the soil with a shovel or cultivator to about 6 inches deep. Do this in spring after the chance of frost has passed. Choose a bed that receives full sun. Zinnias germinate once temperatures reach 70 degrees Fahrenheit.
Sow the seeds approximately 6 inches apart. Plant the seeds in rows or groupings. Cover the seeds with soil to a depth of twice the thickness of the seeds.
Water the seeds with a mist setting or drip irrigation. Keep the soil moist until the seeds germinate.
Spread a 2-inch layer of mulch over the bed once the zinnias form buds. The mulch helps reduce weeds and maintain soil moisture.
Pinch off spent blooms to encourage new flower buds to form. Water zinnias at ground level during drought conditions. Do not water zinnias from above. Check the plants for insects, such as aphids or mites, and treat as needed.