Zinnia (Zinnia elegans) is a dependable summer bloomer that will thrive with very little care, in hot, dry conditions and nearly any soil type. A versatile plant, zinnias are available in single and double forms, in sizes ranging from tiny button blooms to gigantic plate-sized flowers and in heights from 6 inches to 3 feet. Zinnias are available in many colors. The seeds may be sown directly into your flower garden in early spring.
Prepare a spot in your garden where your zinnias will be exposed to at least six hours of sunlight every day. Soil can be any type, but it must drain well. Spade the soil to a depth of 6 to 8 inches, then spade in 2 to 3 inches of compost to improve soil quality and drainage.
Scatter zinnia seeds over the prepared soil, then cover the seeds with no more than 1/8 inch of soil. Spray the seeds lightly, using a garden hose with a spray attachment. Zinnia seeds may also be planted in rows 6 to 18 inches apart, depending on the variety.
Water the zinnia seeds regularly after planting, keeping the soil constantly moist. Once the plants are 6 to 8 inches tall, the zinnias will be drought-tolerant and will need to be watered only when the top of the soil feels dry. Water deeply enough to saturate the roots, then allow the soil to dry before watering again. Water zinnias early in the day, as watering in the evening will create conditions that may invite mildew and disease.
Thin the zinnias when the plants are 2 to 3 inches tall. Refer to the seed packet for spacing, which will vary from 6 to 18 inches, depending on the variety.
Fertilize your zinnias two or three times during the growing season. Use a water-soluble fertilizer or a dry fertilizer with a balanced ratio, such as 10-10-10 or 20-20-20.
Pinch, or deadhead, the wilted zinnia blooms throughout the season. Without regular deadheading, the plant will go to seed early and blooming will decrease. Deadheading will encourage the zinnias to bloom until the end of the growing season.