Late Summer Blues
August bloomers add color, bring butterflies
by Rachel Foster 

The last weeks of summer feature three of my favorite blue-flowered plants: a perennial, a sub-shrub and a potentially large bush. Besides their lavender blue flowers and a late blooming time, they have several things in common. All three appreciate good drainage and lots of sunshine, are loved by butterflies and are pretty much deer-resistant. Although they are easy to grow in ordinary garden conditions, they are relatively drought tolerant and adapt well to low-water landscapes.

Blue Fortune

Anise hyssop (Agastache foeniculum) is a tough perennial in the mint family, native to the prairie states of North America. You can get it from nurseries that specialize in prairie plants, but it’s somewhat easier, these days, to find ‘Blue Fortune,’ a hybrid between anise hyssop and a similar plant from Asia named Agastache rugosa. Both anise hyssop and ‘Blue Fortune’ grow 2-4 feet tall and do best in full sun in dryish, well drained soil. Their slowly lengthening, cylindrical spikes are packed with small flowers that open over a long season and look great with rudbeckia, echinacea, tall sedum and grasses. They are hardier than the agastaches called hummingbird mint, which can have trouble with our wet winters.

Blue mist shrub (Caryopteris x clandonensis), also known as bluebeard or blue spiraea, is a small Asian shrub with fragrant gray-green leaves that blooms on new wood. In cold climates, the topgrowth dies back in winter. Even in mild climates it looks best if cut back in spring. Pruning by one half or more as the buds break keeps it tidy and vigorous. Small flowers are produced over a long period along the top few inches of new growth. Two varieties popular for their strong flower color are ‘Longwood Blue’ and ‘Dark Knight.’ Both are rather upright plants that can reach 4 feet.  

My favorite caryopteris is ‘Heavenly Blue.’ It has powder blue flowers and an excellently neat, mounding habit, but it has become very difficult to find. I recently read about a new variety with deeper colored flowers named ‘First Choice.’ It is said to grow 2-3 feet tall (after pruning) and may turn out to be an acceptable substitute for ‘Heavenly Blue.’ Another low-growing variety is ‘Worcester Gold,’ named for its yellow foliage. All these compact varieties look best where they are not crowded in by other plants and can show off their shapely hummocks. They look great in gravel gardens with rocks, small grasses and strongly architectural plants such as yucca and New Zealand flax. 

And now the big one. Chastetree (Vitex agnus-castus) is an aromatic shrub from the Mediterranean. Like caryopteris, it blooms on new growth and can be pruned quite hard in spring if you need to restrict its growth. In this climate, it is more often grown with minimal pruning as a large bush or small tree and can eventually reach 10-15 feet. Vitex leafs out quite late in spring and quickly produces new shoots clad with attractive three-part leaves. Each shoot  terminates in a densely packed, tapering pyramid of bloom. Vitex extracts have been used since ancient times to regulate the menstrual cycle and promote female fertility. I just know that pollinators love the flowers of this late bloomer, and our voracious deer have never bothered it.

Rachel Foster of Eugene is a writer and garden consultant. She can be reached at rfoster@efn.org