Zinnias are very easy to grow.
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One of the sunniest faces of summer, the zinnia is an easy-to-care for annual. Zinnias, which bloom pink, yellow, white, orange, red, purple and even green, grow in all USDA hardiness zones. They range from 1 foot to 3 feet tall, can spread up to 2 feet wide and are fast growers. Zinnias are among the easiest summer annuals to grow.
Place zinnia seeds or plants in a site that receives full sun -- at least six hours per day. If zinnias don't receive enough sunlight, they will grow leggy, flop over and bloom poorly. Make sure the plants are at least 12 inches apart so they receive good air circulation.
Amend the soil with manure or well-rotted compost. While zinnias are not picky (they'll grow in almost anything), balanced, light soil will ensure good growth.
Water your zinnia plants when the top 2 inches of soil is dry. Zinnias like hot weather; too much water or watering the plants from above can lead to mildew problems. Consider using a soaker hose to keep water near the roots.
Pinch back zinnias when they are between 8 to 15 inches high, depending on whether they are dwarf or standard cultivars. This will encourage branching. Cut off dead blooms to spur new flowering. At the end of the season, leave the final blooms on the plants if you'd like your zinnias to reseed.
Feed your zinnias with Osmocote, Miracle-Gro or another multipurpose 20-20-20 fertilizer once a month.