Gardeners face a challenge as blooms cycle earlier

Crape myrtle — Photo by Anthony Higgins

The August garden is becoming more and more of a challenge, with the bloom-time of all the “old reliables” moving up continually, all cycling through earlier. In the past, I had thought that using more dahlias was a sure-fire way around the dilemma, and it is, one of the few remaining arrows in the quiver of planting ideas. There is this enduring notion about the commonness of dahlias: however that happened, it may be time to chuck it, because dahlias remain with us until frost. Dahlias come in common, cheery colors, to be sure, but also may be woven into the subtlest tapestries of tones and hues.

Most dahlia varieties attain between four and five feet in height and belong at the back of the flower border. A sturdy stake inserted next to the tuber at planting time should accompany the plants for support, and an indelible tag should always identify them. However, careful perusing of catalogues yields many dahlias in the three-foot and mounding two-foot heights. These generally require less or no staking.

The tubers like fertile, well-drained soil in full sun with plentiful moisture. Many growers side-dress the tubers midway through the season. When deadheading or harvesting for cut flowers, make the cut two leaf nodes back from the flower down the stem to keep plants compact and with a low center of gravity.

Flowering shrubs for late summer color

Another strategy for extending bloom, where practical, is the use of flowering shrubs. The Falmouth crape myrtle is, quite literally, one of the first exotic crape myrtle specimens Islanders came to know: it is eye-catching across from the Falmouth Stop & Shop entrance when in full bloom.

Today there are dwarf forms of crape myrtle suitable for the mixed border and container use, and compact forms topping out around eight feet, for the smaller garden. The color range is white-lavender-pink-cerise red-purple. For dwarf subjects use cultivars such as ‘Little Chief,’ ‘Moned’ (red), ‘Pocomoke’ (rose pink), ‘Chickasaw’ (lavender pink), and the Dazzle series, developed by Michael Dirr, with white through pink to red clones.

The National Arboretum maintains a complete listing of crape myrtles at Crape myrtles come in several differing forms, such as vase-like or spreading, have varying attributes such as long season of bloom, resistance to powdery mildew, and fabulous fall foliage color, all of which are noted in this comprehensive list. For island gardens cold hardiness is of course important.

The white, sun-tolerant hydrangeas, in all their forms, are another mainstay of the late summer garden. Tree form “peegees” (short for Hydrangea paniculata ‘Grandiflora’) may top twelve feet and often become magnificent specimens, their large panicles aging to a faded rose that is enchanting. Breeders have selected stock for compact plants; look for cultivars such as ‘Little Lamb,’ ‘Little Lime,’ or ‘Bobo.’ In the midsize range are the cultivars such as ‘Limelight’ and ‘Pinky Winky.’ Prune hard in late winter.

Caryopteris hybrids supply a haze of blue that contrasts nicely with the many yellow-to-gold-to-orange composite flowers that fill late summer beds, such as rudbeckias, heleniums, goldenrods, and Jerusalem artichokes. The latest wrinkle in caryopteris seems to be plants with golden/chartreuse foliage: look for ‘Lil’ Miss Sunshine’ and ‘Sunshine Blue.’

Other, more recent introductions in caryopteris are ‘Petit Bleu’ and ‘Dark Knight.’ These mounders, typically two to three feet tall and wide, like a sunny, free-draining site. Michael Dirr mentions successfully associating caryopteris with santolina and rosemary, which gives a good idea of their cultural requirements. Cut back in late winter/early spring.

All the hypericums deliver golden flowers, notable for their prominent stamens, on neat bushes that are more akin to herbaceous perennials in their culture. Hybrids and cultivars selected from several species make wonderful garden backdrops in well-drained, sunny aspects. Look for ‘Hidcote,’ ‘Sunburst,’ and ‘Sunny Boulevard.’ Plant with caryopteris or globe thistle (Echinops) for that lovely blue-gold combo. Cut back by a third in late winter/early spring.

Harvest time

Vegetables and fruits are ripening, as they should. It is a busy time because this stuff does not wait around, until it is convenient to process them. If not picked and processed promptly, quality in one’s results quickly declines. As someone said about gardening, it is all about the timing.

When some space is left open in the garden, due to harvesting crops and removing spent plants, put in some quick growing or cold tolerant ones. Or plant a cover crop. Fall radishes and turnips do well here, as does kohlrabi. I have planted a form of broccolini called spigariello (Brassica oleracea); it germinates in a flash and yields a bitter green that is good with pasta. From Johnny’s Selected Seeds website: “This variety is technically a leaf broccoli but is grown like broccoli raab…. The flowers of Broccoli Raab are edible. Harvest when the yellow or white flowers open. Add them to any hot pasta or poached fish dish, salads, or flower confetti.”

I have new Swiss chard seedlings, lettuce, radicchio, and leeks. If the plants are grown and ready in cells, very little time is lost between cleaning out the previous crop and installing the new one.

I am indebted to my daughter for pointing out to me where I could make a new bed for strawberry offsets: a different pair of eyes in the garden is really helpful at times. Homegrown garden tour, August 26, 4-6 pm.

Polly Hill Arboretum

Don’t miss Boston University conservation biologist Professor Richard Primack, at Polly Hill Arboretum, Wednesday, August 29, at 7:30. His talk is on leaf phenology, the study of recurring biological phenomena and their relationship to weather. In this illustrated talk, Primack will discuss his on-going research that builds on Thoreau’s observations in Concord in the 1850s, and his own observations of leaves in Japan and at the Arnold Arboretum.