Zinnias are a versatile plant, ranging in appearance and type from eight inches to four feet tall, and including single and double blooms. There are zinnias with dahlia-like, cactus-like, beehive and button flowers.
The flowers also range in color, including whites, yellows, pinks and reds, and even lavenders and greens. The pretty plants are favored for their attractiveness to butterflies, which help pollinate a garden. No matter what kind of zinnia you grow, it will need a full sun location, which will help the zinnia bloom more and grow healthier.
Zinnias prefer well-drained soil, rather than heavy, dense garden soil or clay soils. Prepare the soil in the bed where you want to grow zinnias by turning it and loosening it, mixing in peat moss and sand for drainage, and compost to add organic matter.
Most of the time, zinnias are planted by sowing seed outdoors, as they grow quickly in warm weather, and bloom for a considerable length of time across the growing season. They can be sown in the ground or the garden after the last frost date.
You also can start zinnias from seed indoors, planting them in flats or a seed starting medium 4 to 6 weeks before the last expected frost date. Keep them under artificial lights at a temperature between 75 and 80 degrees Fahrenheit. Seeds should germinate in 6 to 10 days.
Don’t put seedlings out until the temperatures are reliably warm in the spring, as they struggle in cooler weather. For most zinnias, you won’t need to worry about collecting seeds or replanting the following year, as they usually reseed themselves quite well.
Zinnias are heavy feeders, so plan to fertilize them regularly and often, as this will encourage lush, colorful blooming. Use a balanced 10-10-10 or 6-6-6 fertilizer, applying about one pound per 100 square feet for a first spring planting application.
You can apply another round of fertilizer in mid- or late summer, as zinnias will bloom well into the fall with fertilization. Deadheading, or pinching off dead flower blooms, is good for all types of zinnias, and if you want to encourage yours to grow into a bushy, compact shape, you can pinch off the growing tips that try to shoot upward.
Or, if you want to grow them long-stemmed for cut flowers, plant your zinnias closer together and pinch off lower shoots to encourage tall growth instead. Water zinnias regularly, keeping soil moist, but avoid overwatering. Water more in hot climates.
Zinnia Pests & Diseases
The most common problem for zinnias is powdery mildew. To prevent it, be sure there is good air circulation around the plants, and that they are not too close together. Mildew likes cool, wet conditions, so water during the day instead of at night.
Water carefully, directing the water at the base of the plant, into the soil, to prevent water from staying on leaves and stems. Some zinnia growers also use preventative applications of fungicide before powdery mildew develops, since it is so common.
There also are mildew-resistant hybrid cultivars of zinnia now available. Alternaria, or leaf spot, also can afflict zinnias, but can be prevented with good air circulation and regular deadheading. Also pinch off any diseased, dying or damaged parts of the plants and discard them to prevent disease spread.
Zinnias can suffer from insect pests as well, of which the most probably are aphids and spider mites. Pick them off by hand, or wash them off the pants with a targeted stream of water from a spray bottle. Do this during the day, so any residual water evaporates quickly. Regular watering and fertilizing can control insects.
The fertilizing strengthens the plant, and watering helps counteract hot, dry weather, which creates prime conditions for insect pests.
Want to learn more about growing zinnias?
Check out these Web sites chosen by us for more information on the subject.
PennState Extension covers Zinnias for the Home Garden
NC Cooperative Extension covers Zany for Zinnias