#1 Gallon
Platycodon 'Pop Star' is a compact, fast-growing, and hardy perennial (Zones 4-9) that features, ball-shaped, air-filled buds that "pop" open into star-shaped violet-blue, white, or pink flowers. Growing only 6–10 inches tall, they are ideal for borders, containers, and, as noted in this article from Missouri Botanical Garden, are deer-resistant, long-blooming, and low-maintenance. 
 
Key Features and Care:
Appearance: Compact, mounded, grey-green foliage.
Bloom Time: Summer, with continued blooming.
Size: 6–8 inches tall, 10–12 inches wide.
Light: Full sun to part shade.
Soil: Well-drained, sandy, or loamy soil.
Watering: Moderate to low, as stated on the Easy to Grow Bulbs website.
Care: They are long-lived and easy to grow, but they are one of the last perennials to emerge in spring, so mark their spot to avoid damage.