When comparing zinnias in pots or ground, in-ground planting produces larger plants with more blooms and less daily maintenance. But container growing works just fine if you pick the right varieties and give your pots a bit more attention. Neither option is wrong, and both can fill your space with color all summer long.
I ran a side-by-side test with Benary's Giant zinnias two seasons ago. One group went into garden soil. The other went into 14-inch (35-centimeter) pots with premium potting mix. My ground-planted zinnias grew 40 inches (100 centimeters) tall and gave me over 30 blooms each. The potted ones topped out at 28 inches (70 centimeters) with about 18 blooms each. I also had to water the pots every day during July. The garden plants handled three days between waterings just fine.
Container zinnias demand more work because of the limited soil volume. Your pots dry out fast in summer heat since there's less soil holding moisture. Nutrients run out quicker too. Frequent watering washes your fertilizer right out through the holes. Root space puts a ceiling on growth, which is why tall types get stunted in containers. The plants aren't unhappy. They just can't reach their full size.
NC State Extension lists containers as a good way to grow zinnias. Dwarf zinnias for containers solve most of the sizing problems you'll face. These compact types were bred for small spaces and don't fight against pot limits the way tall ones do.
Thumbelina Series
- Mature height: Grows just 6-8 inches (15-20 centimeters) tall, making it perfect for window boxes and small balcony pots.
- Pot size: Thrives in pots as small as 8 inches (20 centimeters) wide since the short root system doesn't need deep soil.
- Bloom style: Produces clusters of small double flowers in mixed colors that create a dense carpet of blooms.
Zahara Series
- Mature height: Reaches 12-18 inches (30-45 centimeters) tall with a compact bushy shape that fills containers well.
- Disease resistance: Fights off powdery mildew and leaf spot better than most varieties, which matters in the humid microclimate around pots.
- Low maintenance: Blooms without deadheading, so you get continuous flowers even if you forget to remove spent blooms.
Profusion Series
- Mature height: Stays around 12-15 inches (30-38 centimeters) with a spreading habit that drapes over container edges.
- Heat tolerance: Handles 100°F+ (38°C+) temperatures without wilting, which is critical for pots sitting on hot patios.
- Bloom count: Produces up to 100 flowers per plant across the season without any pinching or training.
To grow zinnias in pots, start with a container at least 12 inches (30 centimeters) across. Use a potting mix that drains well and make sure every pot has holes in the bottom. Water every day when it's hot outside. Feed your plants a liquid fertilizer every two weeks through the growing season. Don't use garden soil in your containers because it packs down and chokes the roots.
Ground planting wins on ease and plant size. Containers win on being flexible and saving space. Pick based on what you have to work with. A deck full of potted Zahara zinnias puts on just as good a show as a garden bed full of towering Giants. Match the variety to your setting and you won't be let down either way.
I grow zinnias in both spots every year now. My garden beds give me tall cut flowers for the kitchen table. My deck pots give me color right outside the back door where I can enjoy them with my morning coffee. You don't have to choose one or the other. Try both and see which spot makes you happier as a gardener.
Read the full article: How to Grow Zinnia Seeds Successfully
