Zinnia in Zone 7A — Pacific Northwest

Zinnias are a fantastic addition to any Pacific Northwest garden. Their vibrant colors brighten up our mild summers, and their long bloom time means you'll have fresh cut flowers from late June all the way into fall. Plus, those cool nights we get here actually enhance the flower's colors, making them even more spectacular.

While we PNW gardeners do have a shorter growing season of around 183 days and some unique challenges like late blight to consider, zinnias are surprisingly easy to grow with a little planning. You can direct sow or start seeds indoors, and they'll reward you with a profusion of blooms.

Starting zinnia seeds indoors in our region is a good idea if you want a head start, especially since our springs can be slow to warm up. You can start seeds indoors from late March through mid April, about four weeks before you plan to transplant them outside.

Use seed trays with a good seed-starting mix and keep them in a warm spot, ideally around 70-75°F. A heat mat can be helpful, especially with our overcast spring days. Don't forget to bottom water your seedlings to avoid damping off and keep the leaves dry.

Transplant your zinnia seedlings outdoors from early May through early June, once the danger of frost has passed. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the cooler temperatures and stronger sunlight.

When transplanting, space them 6-12 inches apart to allow for good air circulation, which is crucial for preventing powdery mildew. Even though our summers are mild, wet springs can cause problems.

Direct sowing is a perfectly viable option for zinnias in the Pacific Northwest, and it saves you the hassle of starting seeds indoors. Wait until the soil has warmed up a bit, typically from late April through early August. Zinnias need soil temperatures above 60°F to germinate well.

Prepare your garden bed by loosening the soil and amending it with compost. Sow the seeds about ¼ inch deep and space them 6-12 inches apart. Keep the soil consistently moist until the seedlings emerge.

Zinnias need moderate watering, but it's important to get it right, especially in the Pacific Northwest's unique climate. Our summers are dry, but our springs can be quite wet, so adjusting your watering schedule is key. Once established, zinnias are moderately drought-tolerant, but they still need consistent moisture to thrive.

During the spring, when we often get plenty of rain, be careful not to overwater. Check the soil moisture by sticking your finger in about 2 inches deep. If it feels moist, hold off on watering. In the dry summer months, you'll likely need to water more regularly, aiming for about 1 inch of water per week, either from rainfall or irrigation.

Always water at the base of the plants to avoid wetting the foliage, which can lead to powdery mildew in our sometimes humid conditions. Signs of underwatering include wilting leaves and dry soil, while overwatering can cause yellowing leaves and root rot. A layer of mulch around the base of the plants can help retain moisture and suppress weeds, but avoid piling it up against the stems.

Deadheading is essential for keeping your zinnias blooming throughout the season. Simply snip off the spent flowers just below the flower head, encouraging the plant to produce more blooms.

You can deadhead zinnias as needed throughout the growing season, from late June until the first frost. Don't be afraid to cut long stems for bouquets – zinnias thrive on being cut, and the more you harvest, the more flowers they will produce. As the first frost approaches in mid- October, you can let the last blooms fade and dry on the plant, or cut them for dried arrangements.

You can expect your first zinnia harvest in late June if you started seeds indoors, or a bit later if you direct sowed. Zinnias are ready to harvest when the flowers are fully open and the stems are strong.

Cut the stems at an angle, just above a leaf node. This encourages the plant to produce even more flowers. The more you cut, the more they bloom, so don't be shy! Zinnias make excellent cut flowers and have a long vase life, so you can enjoy their beauty indoors as well. As mid- October approaches and the threat of frost looms, harvest any remaining blooms to enjoy indoors before they are damaged.

Zinnias can be susceptible to a few problems in the Pacific Northwest, but with a little care, you can keep them healthy and blooming.

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves, stems, and sometimes flower buds. Leaves may curl, yellow, and eventually die.
• What causes it: Various fungi that thrive in warm days, cool nights, and moderate humidity. Surprisingly, dry leaf surfaces actually favor it (unlike most fungi). Our dry-summer humidity can be just right for this.
• How to fix/prevent it: Improve air circulation by spacing plants adequately and pruning if necessary. Remove affected leaves promptly. Neem oil or potassium bicarbonate sprays can help. A milk spray (1 part milk to 9 parts water) is also surprisingly effective. Choose mildew-resistant varieties when possible.

Bacterial Leaf Spot

• What it looks like: Small, water-soaked spots on leaves that eventually turn brown or black. Spots may have a yellow halo. In severe cases, leaves may drop off.
• What causes it: Bacteria that thrive in warm, humid conditions. Splashing water can spread the bacteria from plant to plant.
• How to fix/prevent it: Avoid overhead watering. Improve air circulation. Remove and destroy affected leaves. Copper-based fungicides may help prevent spread, but are not always effective.

Alternaria Blight

• What it looks like: Dark brown or black spots on leaves, often with concentric rings. Spots may enlarge and merge, causing leaves to yellow and die.
• What causes it: A fungus that thrives in warm, humid conditions. Spores can spread through wind and water.
• How to fix/prevent it: Remove and destroy affected leaves. Improve air circulation. Avoid overhead watering. Fungicides containing chlorothalonil or copper may help prevent spread.

Pacific Northwest Specific Challenges: Our mild summers and dry-summer rainfall patterns mean that while zinnias generally do well here, powdery mildew is a common concern. Giving plants plenty of space and watering at the base are crucial preventative measures. Also, while late blight isn't a direct threat to zinnias, taking general precautions in your garden to prevent it can help overall plant health.

Zinnias make excellent companions for many vegetables in the Pacific Northwest garden. Plant them near tomatoes and peppers to attract pollinators, which will improve fruit set. They also do well alongside squash and cucumbers, helping to deter squash bugs and cucumber beetles.

Avoid planting zinnias near plants that are highly susceptible to powdery mildew, as they can spread the disease. Generally, zinnias are pretty good neighbors and add a splash of color to the vegetable garden.