Zinnias are one of the classic summer flowers that even new gardeners love to include in their yard. Even though zinnias appreciate every bit of sun they can get, they are still a viable option even for gardens that get less than a full day’s worth of sun,
Zinnias can grow in partial shade, where they receive only six hours of sunlight per day. Zinnias planted in partial shade may be shorter and have fewer blooms than those planted in full sun, but they will still produce flowers for pollinators and cutting for bouquets.
If you have a garden or spot in your yard that gets only partial sun and still want to include beautiful zinnias in your spring and summer plantings, keep reading for some tips to help your flowers reach their full potential.
How much sunlight do zinnias need?
Zinnias thrive in eight hours or more of sunlight per day, though they can still grow and perform reasonably well in less sun. The minimum amount of sun they should get each day is six hours. Whether these hours consist of morning sun or stronger afternoon sun doesn’t matter, as long as it’s there.
Because zinnias are native to Mexico and the southeastern United States, they are accustomed to growing in hot and sunny weather. This also explains why they are warm-season annual that can only be planted after all risk of frost has passed.
The last risk of frost in spring is when the temperature is sure to stay above freezing, which will kill zinnias. For most gardeners, this is sometime in April or May.
Zinnias are sun and heat-loving plants
Given that zinnias prefer long days of sun and warmth, wait to plant out seedlings or sow seeds until the soil is consistently at least 50 degrees Fahrenheit. If it’s any colder than that, the zinnia seeds won’t sprout. 60 degrees Fahrenheit or warmer is better and will result in quicker germination.
If your growing season is on the shorter side, then starting zinnia seeds indoors about a month before you plant them in the garden will help ensure you have zinnias ready to grow as soon as the weather warms up and the sun gets stronger.
Direct sowing is also an easy way to get started with zinnias as long as you keep the seeds moist during the germination process. Once they get growing, regular water throughout the season will also help them put on healthy growth and produce continuous flowers.
Whether you decide to start seeds indoors or right in the garden, be sure to choose the sunniest site you have. If your entire yard is shaded for a good portion of the day, you can try planting zinnias in pots.
Sometimes it’s easier to find a patch of sunlight for a pot or two than to make a garden bed that may or may not get the best amount of sunlight for full-sun flowers.
If you need a primer on growing zinnias in pots and containers, this article is right for you: Grow Zinnias in Pots For Container Cut Flowers.
Disadvantages of growing zinnias in partial shade
Strong sunlight will yield long, strong stems for any flower, including zinnias. However, if your zinnias are in partial shade, they likely will be shorter. This doesn’t have to be a deal-breaker, though. You can still enjoy the blooms and cut them for bouquets, albeit shorter ones.
The more sunlight zinnias get, the more flowers they produce because they can produce more energy. So if maximum production is your top goal, choose a sunny location for your zinnias over one that is partially shaded.
Less robust growth
Full sun zinnias can get very bushy with lots of leaf production, whereas those grown in partial shade may be taller without branching out quite as much. Just as with less bloom production, the reason is simply a matter of energy.
Less sun means the zinnia has less opportunity to photosynthesize, or make energy. Less energy equals smaller growth. If you find your zinnia plants are leggy and tipping over, use this article for some tips on standing them back up: 8 Ways To Stop Your Zinnias From Falling Over.
Increased risk of mildew and disease
Zinnias are known for succumbing to powdery and downy mildew by the end of the growing season, no matter how healthy they were before. Similar to zucchini plants, it’s almost inevitable.
For partial shade zinnia patches, it’s possible the powdery mildew will set in sooner. The less light zinnias get, the more shade there is around their leaves. Since sunlight will help kill the spores of fungal diseases like mildew, partial shade may increase the likelihood of them setting in earlier than in full sun.
Best zinnia varieties for partial shade
You can grow any variety of zinnia in partial shade, from taller Benarys Giants to diminutive Short Stuff. Dwarf and compact varieties may fare better with less sunlight because they’re genetically programmed to stay short. They won’t waste energy trying to grow stems as long as the taller varieties.
That being said, you never know how your zinnias will perform in partial shade until you try, so why not include a few standard varieties alongside some shorter ones and see how they turn out?
To read more about the different types of zinnias, check out this article, 5 Types of Zinnias Flowers (Which are the best for cutting?).
Thumbelina zinnias produce single and semi-double blooms in shades of orange, pink, red, purple, yellow, and white. The dwarf plants, which stand 12 to 18 inches tall at maturity, can begin to blossom as early as three inches tall.
Star Starbright zinnia has single flowers that reach about two inches in diameter. The plants themselves top out at about 14 inches on open, bushy plants. This variety has great disease resistance, so you might be able to postpone the arrival of powdery mildew longer, even in partial shade.
The open growth habit of Star Starbright makes them a great choice for hanging baskets. Keep an eye out for hummingbirds!
Large, three inch blooms sit on dwarf plants that don’t quite reach a foot tall. Blooms are in classic zinnia colors of coral, red, white, scarlet orange, and golden yellow. Plant these ones close together to fill in flower beds.
Another dwarf option, the Preciosa series is available in mixes or individual colors such as red, white, orange, and yellow. Even though these plants are compact, the blooms are huge at four inches across. These make a great punch of color in a shady garden area.