Seattle, located in the Pacific Northwest, has a maritime climate with mild summers and relatively mild winters. The city experiences cool temperatures and moderate rainfall during the summer months. Here are some plants that you can consider planting in Seattle during the summer:

1. Annual Flowers: Some annual flowers that thrive in Seattle's summer include marigolds, petunias, impatiens, lobelia, snapdragons, and zinnias. These flowers add vibrant colors to your garden and can tolerate the moderate temperatures and occasional rainfall.

2. Perennial Flowers: Many perennial flowers are well-suited for Seattle's climate. Examples include lavender, black-eyed Susans, coneflowers, asters, phlox, and daylilies. These flowers will come back year after year, providing long-lasting beauty to your garden.

3. Vegetables: Seattle's summer is ideal for growing a variety of vegetables. You can plant tomatoes, cucumbers, zucchini, lettuce, kale, beans, peas, and herbs like basil and parsley. Make sure to provide them with adequate water and sunlight.

4. Shrubs: Shrubs that thrive in Seattle's summer conditions include hydrangeas, rhododendrons, azaleas, camellias, and heather. These shrubs add texture and color to your garden and can withstand the city's mild summer temperatures.

5. Native Plants: Consider incorporating native plants into your garden. Native plants are well-adapted to the local climate and require less maintenance. Some native plant options for Seattle include Oregon grape, red-flowering currant, salal, sword fern, and Douglas fir. These plants also provide habitat for local wildlife.

Remember to assess your specific location, available sunlight, soil conditions, and watering needs when choosing plants. It's beneficial to consult with local nurseries, garden centers, or gardening experts for advice specific to your area in Seattle. They can provide recommendations tailored to the unique characteristics of the city and its microclimates.