Zinnias actually must be planted from seeds unlike many others that grow well from starts. Zinnias are very popular amongst American gardeners because they are easy to grow and they produce big, bright blooms from springtime until winter's first frost. They are an annual flower, which means that you need to plant seeds every year. They come in a lot of saturated colors like white, yellow, orange, red, rose, pink and purple. They also sometimes bloom in multi-color and range in size from about a foot to over three feet tall. Zinnias come in regular variety, with big, flat flowers and they come in cute miniature versions as well. There are over a dozen species of zinnia, some with ruffles of petals and some that more closely resemble daisies. Horticulturists are to thank for all of this variety. Until the nineteenth century, zinnias did not come in many colors and weren't much to look at. Mexicans even knew them as "mal de ojos," meaning sickness of the eye. Today's zinnias are quite another story; in fact, they are the National Garden Bureau's Flower of the Year for 2011.
Zinnias need to be planted from seed. You can pick up zinnia seeds at any place that sells gardening supplies, as they are very common. Sow your seeds indoors four to six weeks before you anticipate the last frost in your area. If you are lucky enough to live somewhere where there is no frost, sow the flowers four to six weeks before you plan to plant your tomatoes. Start by filling a shallow container like a flat, milk carton or individual peat pot with a commercial seed starting mix. Get the mix wet and let it drain. Place your seeds in rows approximately four inches apart. Place three seeds together at every four inch mark. This will make your zinnias easier to transplant later. Cover the zinnia seeds with one quarter inch of seed starter. Spray the mix with enough water to make it slightly moist.
Cover your shallow, planted container loosely with a sheet of clear plastic wrap or place the container in a plastic bag if it is small enough to fit. This plastic will keep your mix from drying as the seeds germinate. Place the container in a bright, sunny location like a window sill. You need to keep the container at 75 to 80 degrees Fahrenheit, so if your window sill is chilly get a heat mat.
Expect to see your first seedlings about one week after you plant your seeds. Once the seedlings sprout, take off the plastic cover. Keep your mix moist by watering from the bottom but don't allow the mix to get soggy or to sit in a puddle. Once all of your seedlings have two sets of leaves, transplant them into larger pots. Place these larger pots in the sunniest place you can find in your house. Otherwise, the plants' stalks will grow too long while stretching for sun and will collapse when the heavy flowers bloom.
Move your zinnias outside once the weather starts to warm up. The zinnias can go out at about the same time as you would plant peppers. Plant your zinnias so that just their roots are covered about 12 inches apart for large flowers and half a foot for dwarf varieties.