There are about 100 species which are included in genus Spiraea. They are mostly woody deciduous or semi-evergreen shrubs with showy spring and summer blooms. The species are widely distributed across the temperate regions of the Northern Hemisphere. The genus name is derived from the Greek speira which means coil or spire and refers to the use of these flowers in garlands and wreaths.
Long arching branches forming mounding shrubs are a common habit for most spiraeas. The leaves alternate each other on the stems and are variable. Some are entire (without indentations), others have margins which are toothed or lobed. Pretty small flowers are grouped together in various forms at the ends of the branches. They are mostly five-petaled, bowl-, cup- or saucer-shaped in shades of pink, purple, yellow and white. Bony follicles which split to expel many small, long seeds follow the flowers.
There are many species and hundreds of cultivated varieties and hybrids grown as ornamentals. Popular selections include the hybrid Vanhoutte Spirea (Spiraea x vanhouttei) which was introduced to gardens in the mid-nineteenth century and still grown today. It is a cold hardy, deciduous, medium-sized shrub which has small, blue-green, diamond-shaped leaves with lobed tips. Clustered white flowers that attract bees, butterflies and ants appear in late spring and early summer. Thunberg’s Spirea (Spiraea thunbergii) is a round, mounding deciduous shrub from China that is covered with thousands of small white blooms in the spring. It is a small shrub whose leaves exhibit showy fall color. Bridal Wreath (Spiraea prunifolia) was introduced to England from Japan in the mid 1800s. It is a airy mounding shrub which is covered in snowy small blooms in the spring. Bridal Wreath Spirea is an old fashioned favorite for borders and informal hedges. A least one species, Spiraea japonica is considered and alien invader in some locations.
Each species, cultivated variety and hybrid has a hardiness range and specific cultural requirements. Most Spiraea are easy to grow and tolerant of a wide range of conditions. Generally, full sun or partial shade in moist but well-drained soil is best for good growth and flowering. Some are aggressive growers and spread via short underground suckers. Prune to shape usually after flowering, some types are best pruned in the early spring. Generally, remove weak and dead stems and older stems back to strong new side shoots. Spireas are lovely in loose borders, masses and hedges. There are dwarf types which are nice as groundcover and in rock gardens.
Plant in spring or fall. Space plants 2 to 15 feet apart, depending on the expected mature size of the plant. Dig a hole only as deep as the root ball and 2 to 3 times as wide. If your soil is in very poor condition, amend the soil you’ve removed from the hole with a small amount of compost. Otherwise don’t amend it at all. Carefully remove the plant from the container and set it in the hole. Fill in around the root ball with soil until the hole is about half filled. Then firm the soil and water thoroughly. Fill the hole with the remaining soil and water again. Form a raised ridge of soil around the perimeter of the hole so it acts like a berm to help hold in water.
Apply a layer of compost under the tree each spring, spreading it out to the dripline (the area under the outermost branches). Add a 2-inch layer of mulch to retain moisture and control weeds. Water plants during the summer if rainfall is less than 1 inch per week. Deadheading spent flowers will sometimes induce a second flowering. Most spireas can be pruned after flowering to reduce height and maintain the desired shape. However, Japanese and bumald spireas should be pruned in early spring to promote the best flowering. Remove dead, diseased, and broken branches anytime. Spireas can be severely pruned and will grow and flower again.
Winchester Gardens generally stocks this item.