Steps for How to Grow Zinnias

Prepare the Soil

• Zinnias grow best in well-drained, moist soil that is rich in organic matter. Cultivate the soil to a depth of 12 inches and amend it with compost or other organic matter. Add sand or peat moss to soil that is compacted, such as heavy clay. Peat moss does not absorb water well when it's dry, so make sure the peat moss is moist before adding it to the soil.

Plant the Zinnias

• Plant the seeds or transplant young plants in an area that receives full sun once the ground temperature reaches 70 degrees Fahrenheit and all danger of frost is past. A soil thermometer put into the ground and left there for five minutes is the best way to know what the soil temperature is. Most varieties of zinnia seeds emerge within seven days of being planted.

Water and Fertilize

• Keep the soil moist, especially right after transplanting young plants or sowing seeds. Water at least once a week at ground level early in the morning, since zinnias are prone to powdery mildew. Fertilize zinnias on a regular basis to encourage larger blooms. Follow the label directions on the fertilizer of your choice in regard to how much to use and how often to apply it.

Stake Taller Varieties

• The taller varieties of zinnia often require staking to keep them upright, especially if you live in an area prone to high winds. Insert a stake at the base of each individual plant when it's young, so you can train the stem on the support as the plant grows, or use several stakes and twine to stake a bunch of zinnias up as a group. The number of plants you're growing as well as how close together they're growing is the determining factor for deciding which staking method is best.

Deadheading and Seed Saving

• Deadhead the faded flowers to encourage zinnias to continue blooming all season long. Deadheading is the term gardeners use for cutting off the faded flower heads. At the end of the growing season, be sure to leave some of the faded blooms on the plants. Once the flower head and the stem turns brown, remove the seed heads. Break the seed heads open to reveal the zinnia seeds inside. Lay these out in a single layer to dry for two weeks, then put them in a sealed container to plant the following spring.