It’s recommended that you grow zinnia from seed right in the garden bed, as they do not like to be transplanted and do not often thrive. From seed, they will grow very quickly in the right conditions.
Note:Zinnias can be started from seed indoors if you prefer—just transplant them while they’re young and do so carefully.
Zinnias are sensitive to frost, so do not seed until the last frost has passed.
Zinnias will grow in a minimum daytime temperature of about 60°F (16°C), though a range of 74–84°F (23–28°C) is preferred.
Sow a round of seeds every week or so for several weeks to extend the flowering period.
CHOOSING AND PREPARING A PLANTING SITE
Choosing a location that gets full sun is essential.
Good air circulation will help to prevent foliar diseases such as powdery mildewlater in the season.
Zinnias are adaptable to most soil conditions, but the ideal soil will be rich in organic matter and well-drained.
Soil Ph should be between 5.5 and 7.5.
If soil is amended with compost, the flowers will grow more quickly. Learn more about soil amendments and preparing for soil
HOW TO PLANT ZINNIAS
Space plants 4 to 24 inches apart, depending on variety. (Many common varieties are planted 6 inches apart within the row and 2 feet in between rows.) See back of seed packet for variety-specific advice.
Sow zinnia seeds only about ¼-inch deep.
You’ll see zinnia seedlings in only 4 to 7 days for most varieties, though it will be anywhere from several weeks to a couple months before blooms appear (depending on planting site and climate).
When seedlings reach three inches tall, thin them so that they’re 6 to 18 inches apart to maximize air circulation. This reduces the chance of powdery mildew developing.