This grower is fairly sure of this plant identification.
Other larger spirea japonica in larger pots available at higher prices.
Spiraea, Japanese spiraea
Spiraea japonica (Spiraea). This is a deciduous shrub, which has a dwarf form. Mass planting is very effective and will provide blooms all summer long. To keep a good shape, prune after flowering.
They will thrive in most garden conditions, they will prefer a warm summer. Grow them in moist, well-drained soil and sheltered from hot sun, especially in warm summer areas.
Ornamental, border, container, window-box, ground-cover. Summer interest.