Zinnia Growth Factors

Sunlight

• Zinnias do best in full sunlight. Because the range where these flowers will grow is wide, ones grown in the deep south -- Zones 9 through 11 -- or in the desert will benefit from some midday or afternoon shade to prevent them from suffering from heat and water stress. Full sun is defined as six or more hours of direct sunlight.

Spacing and Air Circulation

• It's very important that zinnias be spaced properly and not planted to the point of overcrowding. While zinnias are very low-maintenance and prone to few pests or disease problems, they will succumb to powdery mildew if planted too closely together. Spacing plants properly -- as recommended on the seed packet or the planting tag -- will increase air circulation and allow plants to dry off after watering, preventing fungal diseases.

Soil

• Zinnias require well-draining soil to thrive. If the soil in your garden is heavy clay, or you know it to be generally poor, amend it with compost to make it drain better and provide supplemental nutrients. If the soil hasn't been worked in a while, rent a rototiller and make a few passes to break up any soil clods. This step is especially important if you're planting zinnia seeds because they require a well-worked, loose soil in order to germinate.

Moisture

• Zinnias are pretty drought-tolerant, but they do need some regular moisture, especially if they're container plants, which dry out much more quickly than zinnias growing in the ground. Water zinnias at ground level. A drip irrigation system is perfect for watering zinnias because it keeps the water off the foliage, but if not, watering with the hose or a watering can is fine, as long as the foliage isn't dampened in the process.

Trimming and Staking

• Zinnias will generally look better -- they'll be bushier -- and will produce more blooms if the flowers are routinely trimmed. That shouldn't be a problem because they make excellent additions to flower arrangements. Taller varieties of zinnia should be staked to keep them from leaning, especially if they're part of a cutting garden and you want straight stems for bouquets. The heads can get heavy for the stems on tall varieties and metal hoop staking around plants can help.