Zinnia elegans has lance-shaped, rough leaves, but other varieties have broader, less scratchy leaves. Flowers are rounded and may be daisy-like, double, cactus-flowered, or a formal-looking dahlia-type. Zinnias flower all summer and often into fall, lasting in the garden from two to five months. Zinnias are most robust during the hot summer and the warmest spring and autumn months. Zinnias don’t need to be deadheaded, but your plants may have a longer bloom period if you do. As the weather warms up in the spring, start planning a day when you can plant your zinnias. Zinnias are one of the few plants that are true annuals, meaning they do not come back every year. You will need to plant new seeds or starts every growing season. They can withstand some of the worst growing conditions but make sure to give zinnias full sun. Zinnia plants can take a few weeks to become established, but once it warms up, expect them to bloom from late spring through fall. The vibrant, tropical colors of zinnias work well in a hot border, picking up the hues of other reds and oranges. They are also nice for adding dramatic color to a container. The tall Zinnia elegans is still a favorite for the back of the border, but new varieties, like the ‘Thumbelina’ series, grow only about 6-inches tall and make great choices as edging plants or in containers.
Planting and Soil
Zinnias are best planted in the spring. Zinnias are not picky about their soil but need their space. So, if you’re planting a smaller variety of zinnia seeds, leave at least 6 inches between plants. Larger types of zinnias need at least 12 to 18 inches between plants for proper air circulation and disease prevention. When sowing zinnia seeds, you can put two or three seeds in each hole to increase your chances of a seed germinating in that spot. However, if two or three plants sprout, remove the weakest seedlings once they’ve grown two to three inches. Keep only the most robust one. The soil you use must be well-draining. If your soil is poor, you can add some compost to give the plants a boost, but zinnias will grow in even bad soil. Zinnia roots can’t tolerate damp soil. Excess moisture can lead to the flowers getting a fungal infection, like powdery mildew. It helps to have a soil pH in the neutral range, but it’s not mandatory.
Light
Plant zinnias in a spot with full sun. You will get the most prolific blooms in a sunny spot, and it will help to keep the leaves dry and thwart powdery mildew before it starts.
Water
Zinnias are very drought tolerant and don’t usually need any supplemental watering.
Temperature and Humidity
It doesn’t matter how hot the summer gets; zinnia plants just keep on blooming.
Fertilizer
Zinnias are easy-going plants, needing only occasional feeding with a well-balanced fertilizer. For the amount to use, follow product label instructions.
Types of Zinnias
Some varieties are spreading, dwarf zinnias only grow about 6 to 8-inches tall, and the classic zinnia elegans can reach 4 feet tall. Here are some types to try:
‘Thumbelina’: Multi branching flowers that reach 12 to 18 inches tall with semi-double and double 2-inch blossoms in rich pink, salmon, lavender, purple, pumpkin, crimson, and yellow ‘State Fair’: Tall stems with large dahlia-type blooms, ranging from 3 to 5 inches wide, with double and semi-double blooms that come in red, purple, salmon, yellow, white, and lavender ‘Zahara’: Mildew resistant with large flowers ‘Dreamland’: Double flower heads on a compact dwarf plant ‘Envy’: Semi-double chartreuse flowers that are 30 inches tall ‘Orange Star’: Orange flowers; bushy dwarf Creeping Zinnia (Zinnia angustifolia): Also called narrow-leaf zinnia, these compact and bushy plants have branching stems and smooth, thin-leaved foliage with bright orange, yellow, white, red, and pink blooms
Pruning
Zinnias make great cut flowers for bouquets. The more you pick, the more they bloom. Or you can deadhead zinnias for a longer blooming period, but it’s unnecessary. They may pause flowering for a while, but they’ll start up again.
Propagating Zinnias
There are several ways to propagate zinnias: by division, using already established plants, or with cuttings.
How to Grow Zinnias From Seed
This plant is extremely easy to start from zinnia seeds. You can direct sow as soon as the soil has warmed, and there is no chance of frost. Sow seeds about 1/4 inch deep. You can also start seed indoors, about four to six weeks before your last frost date. Every garden center has zinnia seedlings for sale if you don’t have seeds saved; however, you will have less choice of varieties.
Potting and Repotting Zinnias
You can start all zinnia seeds in small pots, but only shorter zinnia varieties can remain in pots. Tall zinnias do not do well in pots. If you must stick to a container garden, consider using hybrid bedding zinnias that tend to have a short, spreading growth habit.
Overwintering
Zinnias are annuals. The only way to keep them going through the winter is to dig them up and bring them inside.
Common Pests and Diseases
It is rare for zinnias to be bothered by insects and most four-footed animals show no interest in them. Some varieties can be very prone to powdery mildew. It’s ugly, but it’s unlikely to harm your plants. To cure, clip back the parts of the plant that are affected. Then, apply a fungicide with neem oil, potassium bicarbonate, copper, or sulfur.
