Spirea

Posted by shane - February 11, 2015 - A-Z Plant Maintenance, Shrubs - No Comments

Spiraea japonica cvs.

Spiraea trilobata (3-Lobed Spirea)

Spiraea x ‘Arguta’ (Dwarf Garland Spirea)

Spiraea x bumalda cvs.

'Goldflame' spirea

‘Goldflame’ spirea

There are many Prairie-hardy varieties of spirea, and it is one of the most common ornamental shrubs in Alberta, often planted with potentilla, barberry, and juniper.  There are early-flowering white varieties, and many late-flowering summer varieties, with varied flower and foliage colour.  A healthy spirea shrub can be a nice addition to the shrub bed.  The trouble is, it is uncommon to see a truly healthy spirea in our region.  Like roses, spirea are prone to severe winter-kill, and more often than not, specimens look half dead until mid-summer.  Older, neglected shrubs appear messy, and to make matters worse, most specimens I encounter have been mutilated by the power hedgers, leaving them torn, ragged, and unsightly.  Most arborists I speak to agree that spirea doesn’t have a place in most Prairie gardens.  Unfortunately, the landscapers don’t agree and these plants are everywhere.

The nicest specimens I saw were in Anders on the Lake in Red Deer, growing in a deep, irrigated, raised planter.  They were truly stunning and looked as good as spirea can in Alberta. Ironically, the client wanted us to rip them out and replace them with hydrangea.  Normally I applaud someone for removing their spirea plants, but in this case, I was reluctant.

3-lobed spirea

3-lobed spirea

As with potentilla, if you really are enthusiastic about planting spirea, I suggest you give it the best start you can.  Choose only healthy stock from a reputable source.  Avoid buying these plants at hardware stores! Plant spirea in a deep, well-drained garden loam, with a 2-3 layer of wood chip mulch surrounding the plant, but not contacting the stems.  Make sure the plant stays evenly moist throughout the first growing season. The mulch will hold moisture and protect the plant roots, and supplementary irrigation shouldn’t be that important in successive years.

I prefer the white varieties over the purple, as they seem to be more reliable.  Dwarf Garland spirea looks excellent in a mixed planting with shaped dwarf Korean lilac, mugo pine, with an icee blue juniper ground cover.

Exposure

Full sun.

Pruning Time

In summer, to remove dead patches and dead seed-heads.  If a sheared specimen is desired, shear from late Fall to mid-Spring, prior to bud-break.

Pruning

Spireas are frustrating to prune because of the messy appearance and shear volume of die-back normally present.  If the plant is 1/3 dead or more from winter-kill, I often choose a hard renovation (ie. cut the back to about 3″ above grade) and grow a new plant from the existing roots.  This doesn’t always work because the roots might not have the energy to grow a new plant.  A plant that is half-dead in Spring is a good candidate for removal and replacement. Otherwise healthy plants may just need a very light shearing to remove the dead seed-heads.

Shaping

Well-suited to light shearing.  Avoid hard cutting.  The summer-flowering varieties are a perfect shrub size at maturity and, rather than constantly shaping these plants, it is much better to let them grow to maturity, and simply remove the dead flowering tops each year.  The white-flowered varieties are best left un-sheared, as they look best in their natural, cascading form. Simply reduce the length of a few wayward, or aggressively growing, branches each summer.

(c) 2015 Shane LePage, Wild Rose Garden & Tree Service, Red Deer, AB.