Give Zinnias a Head Start Indoors To Enjoy Blooms From Summer Into Fall

Last week we began looking at the once maligned zinnia as an ornamental garden plant and flower that is showing a resurgence in popularity due to breeding work done in the past decade.

When discovered by a German professor of medicine in the 18th century he referred to them as the Brazilian marigold, but in fact, zinnias can be found throughout the Americas with native species also found in the American Southwest. They were undoubtedly found in your grandmother’s garden but may have been avoided by a generation as being passé. It’s time though to bring them back into the garden as they’re easy, versatile and colorful annuals.

Aside from their color, zinnias also attract butterflies and hummingbirds and will also attract beneficial insects that assist in reducing the populations of the baddies such as aphids and mites. Keep in mind that this is not considered to be a valuable pollinator plant.

One of the other great things about this plant is that the seeds are rather large and easy to handle. This makes them easy to start from seed both indoors and out, and because of their size the seed is easy to handle by children as well as older adults. Those who wish to get a jump on the season can start them indoors, on or after March 13. If you want an extended season of bloom you can start them indoors with several seedlings 10 days apart or in situ outdoors with seeding starting in late April. Succession sowing outdoors every two weeks until mid-Summer guarantees plants in bloom well into the fall garden. This plant is frost tender though it may continue to bloom into late October or early November.

For children or grandchildren, the seed is easy to handle and can be sown in a number of ways. If they want to grow lots of them make sure they’ve thought about where they’ll be planted (they can go into large pots instead of into the garden). The seeds can be sown into small cells and then you get the chance to teach the kids about transplanting as they get moved into larger pots or the garden. A great experiment could be to start some plants indoors then also start some seeds outdoors and do an ongoing comparison to observe the differences. Will the outdoor seeded ones catch up to the ones started indoors weeks earlier? Show them that even the ones that only grow a foot tall still have the same flower form as the ones that grow 3 feet tall. The size of the flower may be different, but the flower itself looks the same when size isn’t considered.

You can wait until May and buy your zinnias as potted plants or in flats, but if you go this route you’ll be seriously limited to the most popular varieties, which may not be the best or the ones you want. That’s why I’d encourage you to at least grow some of your zinnias at home so you can make your own choices — and there are many.

These are plants that grow rapidly from seed and should be started four to six weeks before our last frost, which means starting them indoors in this area any time from late March onward. The seeds can also be sown directly in the garden after the threat of frost late in April. Simply fill a shallow container (flat) or individual peat pots or peat pellets or plastic cells and moisten appropriately. Sow the seeds individually or in rows so they will be easy to separate when it comes time to thin or transplant. In pots, sow three to four seeds in each pot. Cover the seed lightly with a layer of starting soil and mist the top to moisten it. The soil needs to be kept warm and moist but not wet — a trick some never quite learn.

The seeded flat can be covered with a clear plastic dome, or a tent can be made with clear plastic that will retain heat and moisture. If kept in bright light but not sunlight at room temperature the soil should stay warm enough for the seed to germinate though some use heating mats to warm the soil. Keep the flat moist — not dripping wet — and when you water use warm, not cold, water while the seeds germinate.

The flat or pots should be in a bright, warm spot or under grow lights, but always out of direct sunlight, which will just cook them. That is, unless you have a sunny, warm window and choose not to enclose the flat/pots in plastic. Seedlings should emerge in six to 10 days. Remove the plastic or dome and keep the soil evenly moist, not soggy and don’t add any fertilizer.

When the seedlings have at least two sets of true leaves, transplant them into pots that are 2 ¼ inches or larger. Provide as much sunlight as possible so the young plants don’t get leggy from stretching for sun. Plant outdoors when the weather and soil are warm, preferably on a cloudy day in May, at just about the same time you’d plant peppers or impatiens.

As the plants mature and begin to bloom, always remove the spent flowers to keep the plants robust and blooming. Even those types that don’t need deadheading always look better when the spent blooms are removed. Water regularly and feed twice during the growing season with a balanced liquid feed such as 10-10-10 or use a timed release product such as Osmocote at planting. If using an organic fertilizer use one with the highest phosphorous number (the middle number) that you can find. As the season progresses use an organic liquid fertilizer or add an organic granular fertilizer to the soil as per the product’s instructions. Remember that an organic granular fertilizer is naturally longer lasting than the expensive commercial liquid fertilizers such as Miracle-Gro. Blooming will continue well into the fall until we get a frost.

One of the biggest problems with zinnias has been their susceptibility to powdery mildew, which is a fungus. And no, the zinnias can’t get it from other plants such as lilacs or roses as this disease is host specific, meaning it can’t spread from one plant family to another. As just about every East End gardener knows, our warm and humid summers are the perfect breeding ground for powdery mildew. The best way to keep them mildew free is to keep the foliage dry (avoid overhead, automatic irrigation systems), provide good air circulation and remember that the angustifolia and haageana types are more mildew resistant than elegans.

The interspecific crosses of elegans and angustifolia such as Profusion will provide the very best mildew resistance (and is an All-American Selections winner) while the varieties Old Mexico, Orange Star, Pinwheel Star, Profusion Cherry, Profusion White and Star White are also noted as having good mildew resistance.

Other varieties that show good mildew resistance are the Benary Giant Series, which have 4-to-6-inch flowers, and the Double Zahara Brilliant mixture, which are 15 to 20 inches tall with double-type flowers.

Johnny’s Selected Seeds has a great range of varieties and types of zinnias with about 30 or so offerings of every type and size included. Check these out either online or in their print catalog. Johnny’s has seed packets with as few as 15 seeds but most start around 50 seeds to a packet and cost about a dime a seed and up. For large cutting gardens there are packets of 250 and 500 seeds.

While there are chemical controls for powdery mildew there are also effective biological and organic controls, but they must be used at the first sign of powdery mildew. Light horticultural oils such as SunSpray are effective as are fungicidal formulations of neem oil extract and potassium bicarbonate. All are available at the better local garden centers. Never spray the plants when it’s very hot and very sunny.

There is a zinnia relative that’s a look-alike referred to as the creeping zinnia, Sanvitalia procumbens. You may have seen it being grown in hanging baskets, on slopes or used as a creeping ground cover in very hot and dry locations. The flowers are daisy-like golden yellow with brown eyes or centers. Growing 6 to 8 inches tall and spreading as much as 30 inches, they resent being transplanted as seedlings so they’re best grown directly in pots then moved to the garden or purchased in packs at the garden center. Mandarin Orange and Gold Braid are two of the most popular varieties. Keep growing.