Get It Growing: Plant happiness in your garden with zinnias

By Clallam County Master Gardeners • March 16, 2022 1:30 am
Zinnias have a variety of blossom shapes including daisy-like flowerheads with a single or double row of flat petals (as shown here), flowers with multiple rows of petals and no visible center, and dome-shape blossoms that look somewhat like a beehive.
Zinnias have a variety of blossom shapes including daisy-like flowerheads with a single or double row of flat petals (as shown here), flowers with multiple rows of petals and no visible center, and dome-shape blossoms that look somewhat like a beehive.

Zinnias are an old-fashioned flower that remain popular in many home gardens. Why is that?

You may not know that zinnias:

• are low maintenance plants; once established, zinnias are drought tolerant and resistant to most pests, and need minimal attention from the gardener

• come in a variety of plant sizes; the low-growing, creeping varieties are great for borders, flower beds and containers, and the taller varieties produce big blossoms that make a statement in the garden and are ideal for bouquets

• bring an explosion of color and pizzazz wherever they are planted, with their rainbow of colors and interesting shapes.

Planting

Plant zinnias in the garden when soil temperatures reach 60 degrees or higher (typically May or early June on the North Olympic Peninsula).

Zinnias usually are grown from seed; some nurseries, however, sell starter packs and potted zinnias. To save money and have the greatest selection of varieties, plant zinnias from seed.

You can start your own seeds indoors, but you will need a warm spot and supplemental lighting such as grow lights or fluorescent light bulbs. Plant seeds early enough so starts can be transplanted outdoors as soon as the weather warms. On average, zinnias take about a week to sprout and another three to five weeks to reach a transplantable size.

Zinnias have a variety of blossom shapes including daisy-like flowerheads with a single or double row of flat petals (as shown here), flowers with multiple rows of petals and no visible center, and dome-shape blossoms that look somewhat like a beehive.

Zinnias have a variety of blossom shapes including daisy-like flowerheads with a single or double row of flat petals (as shown here), flowers with multiple rows of petals and no visible center, and dome-shape blossoms that look somewhat like a beehive.

Zinnias will adapt to many soil conditions but do best in soil that drains well and is rich in organic matter.

To increase blooms and minimize diseases, plant zinnias in full sun (six or more hours of direct sun daily).

Sow seeds about a quarter-inch deep. Space seeds as recommended on the seed packet, usually 8-18 inches apart. If zinnias are planted too closely, they will produce tall, skinny plants with small flowers.

Care

Because the seeds are planted relatively close to the surface, they will dry out quickly. Mist the planting area frequently (as opposed to watering it with a hose or watering can) to minimize disturbance of the seeds.

Once the seedlings are 3-4 inches tall, switch to an occasional deep soaking. Zinnias need about 1 inch of water a week. Water plants at soil level to keep leaves and flowers dry. Once established, zinnias are relatively drought tolerant.

To encourage branching, snip the top 3-4 inches off the plants when they are 8-12 inches tall. Prune just above a set of leaves. Tip-pruning can delay the production of flowers, which might be an issue in cooler growing areas. If you do not tip-prune your zinnias, be prepared to stake taller varieties.

Zinnias do not require much fertilizer. When plants are a couple of inches high, with multiple sets of leaves, apply a water-soluble balanced fertilizer (one with similar amounts of nitrogen, phosphorus and potassium) once a month following the manufacturer’s directions.

Harvest zinnias for bouquets when the petals are open, and the stem is firm. To tell if a flower is ready for cutting, grab the stem about 8 inches below the flowerhead and wiggle it; if it bends, that flower is not ready for harvest. Wait a few more days.

If you don’t harvest your zinnias, remove (deadhead) spent blossoms regularly to promote more flowering. Cut the stems just above a set of leaves to encourage additional blossoms.

A common problem

Powdery mildew (a fungal infection that produces white spots on the surface of leaves) is a common problem among zinnias. Unlike other fungal diseases, powdery mildew is spread by wind, not surface moisture. As a result, powdery mildew often occurs late in the growing season when the weather is drier.

Many newer varieties of zinnias have resistance to powdery mildew. Adequate spacing between plants and judicious use of fertilizers will help further discourage the disease.

If you see powdery mildew in your garden, you can limit its spread by removing affected leaves and shoots as soon as possible. Spraying plants with selected fungicides can also help. See pnwhandbooks.org/plantdisease/host-disease/zinnia-powdery-mildew for recommendations.

With proper spacing and good watering practices, problems will be limited and your zinnias will add not only a burst of color to your garden, but a bit of happiness.

Jeanette Stehr-Green is a WSU-certified Clallam County Master Gardener.

‘Harnessing the Power of Heat Units’

Make sure to join us for the upcoming Green Thumb presentation “Harnessing the Power of Heat Units for Your Garden’s Success,” by Laurel Moulton, Clallam County Master Gardener Program Coordinator, from noon-1 p.m. on Thursday, March 24, on Zoom. Find the link at extension.wsu.edu/clallam/master-gardener-calendar. Presentations cover basic gardening topics relevant to most home gardeners. Seminars are free, but donations to help support the WSU Clallam County Extension Master Gardener program or Master Gardener Foundation of Clallam County are appreciated.