Zinnia

Zinnias (Zinnia elegans) are upright, flowering annuals in the aster family, originally from Mexico. They’re colorful, easy to grow and attract pollinators.

Height depends on the variety and on growing conditions, from dwarf bedding types about 8–10 inches (20–25 cm) tall to cut-flower varieties over 3 feet (1 m). The taller varieties make excellent cut flowers. Zinnias flower from summer into early autumn.

Wait for warm weather. Zinnias can’t take cold, so sow them in spring, not autumn. Outdoors, sow seeds directly in the ground after your last frost date, about ¼ inch (6 mm) deep. For a long supply of cut flowers, sow again every 2 weeks.

Starting indoors. Sow in trays about 4 weeks before you plan to plant out, and cover the seeds. At 80–85 °F (27–29 °C) they sprout in 3 to 5 days; at 70–75 °F (21–24 °C) it takes 5 to 7 days. Don’t start too early: young plants set out while nights are still cool tend to sulk and catch diseases. Try not to let seedlings become root-bound or to disturb their roots.

Plant out after frost. Move plants outside only once all danger of frost has passed.

Sun and soil. Zinnias grow best in full sun all day; in partial shade they’re more prone to leaf spot diseases. They like fertile soil rich in organic matter and a warm, sheltered spot that drains well. In cold places or heavy soils that stay cold and wet, they struggle.

Spacing. Gardening experts space plants 9–12 inches (23–30 cm) apart, while gardening experts suggest about 12–16 inches (30–40 cm) when growing them in a block. Check your seed packet for your variety.

Pots. Zinnias grow well in containers too. Put them in a sunny spot and use a good-quality potting mix.

Watering. Water zinnias in hot, dry weather, but try to keep the leaves dry, since wet foliage encourages fungal disease. Water at the base of the plants; if you do water from above, do it early in the morning so the leaves dry quickly.

Feeding. Plants in containers benefit from a high-potassium feed, such as tomato feed, once they’re in flower.

Pinching. When plants are about 8–12 inches (20–30 cm) tall, pinch out the central growing tip just above a pair of leaves. You may lose the first flower, but you’ll get more flowers in the long run.

Deadheading. When a flower starts to lose its color, cut it back to another branch so the next bud can open.

Support. Gardening experts say no support is necessary, but gardening experts suggest netting for taller varieties grown in a block.

Zinnias have few insect pests, but aphids, spider mites and whiteflies can damage plants, especially in hot, dry weather. Aphids and spider mites can be hosed off with a strong stream of water. Japanese beetles may also show up, and slugs can ravage seedlings.

The main diseases are powdery mildew (a grayish-white, powdery coating), Alternaria leaf spot, bacterial leaf spot and aster yellows. Seedlings can damp off in cold, wet weather, and older plants can get gray mold (botrytis). Keeping the leaves dry and clearing away plant debris at the end of the season helps prevent problems, and some cultivars have shown good resistance to leaf spot.

Because zinnias feed many beneficial insects, gardening experts recommend using no insecticide other than insecticidal soap.

Cut zinnias for the vase before the flowers are completely open, once the stem feels firm from the cut up to just below the bloom. Handle them gently: the stems are hollow and crush easily, which shortens vase life. Cut zinnias last about 7 to 10 days.

Saving seed isn’t always worthwhile. Many zinnias are F1 hybrids that don’t come true from seed, and seed from plants that had leaf spot diseases can carry the disease, so don’t save it.

Keep cut stems cool, at 40–50 °F (4–10 °C), but no colder: zinnias are sensitive to cold damage.

Pet poison experts list zinnias as non-toxic to dogs, cats and horses, and gardening experts also tags them as non-toxic for cats and dogs.