Zinnia Plant Guide
1. Zinnia Types & Varieties
Zinnias come in a fantastic range of forms, from small, single daisies to large, dahlia-like blooms. They are typically classified by their flower shape and height.
Flower Shapes:
Single-flowered: Have a single row of petals, with a visible center. (e.g., 'Profusion', 'Starfire')
Semi-double flowered: Have multiple rows of petals, but the center is still somewhat visible.
Double-flowered: Have many rows of petals, completely obscuring the center. (e.g., 'California Giant', 'Benary's Giant')
Dahlia-flowered: Large, dense, double blooms resembling dahlias.
Cactus-flowered: Petals are rolled and pointed, giving a spiky appearance.
Pompon/Lilliput: Small, compact, double blooms.
Scabiosa-flowered: A dome of small petals surrounded by a ring of larger petals.
Height Categories:
Dwarf (6-12 inches): Great for edging, containers, or front of borders. (e.g., 'Thumbelina', 'Profusion' series)
Medium (1-2 feet): Versatile for borders and cutting. (e.g., 'State Fair', 'Oklahoma' series)
Tall (2-4 feet): Ideal for the back of borders and serious cutting gardens. (e.g., 'Benary's Giant', 'California Giant')
2. Planting
When to Plant: Zinnias are sensitive to cold and should only be planted after all danger of frost has passed in your area, and the soil has warmed up (typically when nighttime temperatures consistently stay above 50°F / 10°C).
Direct Sowing: This is the easiest and most common method. Sow seeds directly into the garden bed. Zinnias germinate quickly (5-10 days).
Starting Indoors: If you want an earlier bloom, you can start seeds indoors 3-4 weeks before your last frost date. Be gentle when transplanting, as zinnias can be sensitive to root disturbance.
Location:
Sunlight: Zinnias are true sun-lovers! They need at least 6-8 hours of direct sunlight daily for the best blooms. Less sun will result in leggy plants and fewer flowers.
Soil: They prefer well-drained soil that is moderately fertile. While they aren't overly picky, avoid heavy clay or overly sandy soils.
Improving Soil: Amend with compost or other organic matter to improve drainage and fertility.
Air Circulation: Good air circulation is crucial to prevent fungal diseases like powdery mildew. Avoid planting too densely.
How to Plant:
Direct Sowing: Plant seeds about 1/4 inch deep and 4-6 inches apart. Once seedlings emerge, thin them to their recommended spacing (which varies by variety, usually 6-18 inches apart for mature plants).
Transplanting: If starting indoors, harden off seedlings for a week before planting them outdoors. Plant at the same depth they were in their pots.
3. Watering
Initial Watering: Water thoroughly after planting seeds or transplanting seedlings.
Established Plants: Once established, zinnias prefer consistent moisture but do not like soggy feet.
Water deeply at the base of the plant to keep foliage dry, as this helps prevent fungal diseases.
Allow the top inch or two of soil to dry out between waterings.
During hot, dry spells, they may need daily watering, especially if in containers.
4. Fertilizing
Zinnias are not heavy feeders. If your soil is reasonably fertile, they may not need much, if any, additional fertilizer.
When to Fertilize: If your soil is poor or you want to encourage more blooms, you can apply a balanced liquid fertilizer (e.g., 5-10-5 or 10-10-10) every 2-4 weeks, or use a slow-release granular fertilizer at planting time.
Avoid Excess Nitrogen: Too much nitrogen can lead to lush, leafy growth at the expense of flowers.
5. Pruning & Deadheading
Pinching (Optional but Recommended): When young zinnia plants have developed 2-3 sets of true leaves, you can "pinch" back the main stem (remove the top 2-3 inches). This encourages the plant to branch out, resulting in a bushier plant with more flowers.
Deadheading: This is key for continuous blooming! Regularly remove spent or faded flowers. This prevents the plant from putting energy into seed production and encourages it to produce more blooms.
Cutting for Vases: When cutting zinnias for bouquets, treat it like deadheading. Cut the stem long, just above a set of leaves or a branching point. This encourages the plant to produce new, strong side shoots.
6. Pests and Diseases
Zinnias are generally robust, but they can encounter a few issues:
Pests:
Aphids: Small, soft-bodied insects that cluster on new growth. Blast them off with a strong stream of water or use insecticidal soap.
Spider Mites: Tiny pests that cause stippling on leaves, especially in hot, dry conditions. Look for fine webbing on the undersides of leaves. Increase humidity and use insecticidal soap.
Japanese Beetles: Can skeletonize leaves and flowers. Hand-pick them or use appropriate controls if infestation is severe.
Diseases:
Powdery Mildew: The most common zinnia problem. It appears as a white, powdery coating on leaves, especially in humid conditions or when air circulation is poor. Choose resistant varieties, ensure good air circulation, and water at the base of the plant. Fungicides can be used for severe cases.
Bacterial Leaf Spot/Blight: Dark, irregular spots on leaves. Remove infected leaves and improve air circulation.
Alternaria Leaf Spot: Brown spots with concentric rings.
Prevention: The best defense against diseases is proper cultural care: good air circulation, well-drained soil, and watering at the base of the plant.
7. Attracting Pollinators
Zinnias are absolute magnets for:
Butterflies: Especially the larger varieties with flat tops that provide a landing pad.
Bees: All types of bees love zinnia nectar and pollen.
Hummingbirds: Attracted to brightly colored varieties.
Planting zinnias is a surefire way to bring life and vibrant color to your garden from early summer until the first hard frost. Enjoy their prolific blooms!