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(Agapanthus praecox ssp orientalis 'Getty White’) The Agapanthus has been called “Lily of the Nile” but it's not a member of the Lily plant family and is native to South Africa, a long way from the Nile River. The Getty White Agapanthus contrasts with dark blue varieties. (Contributed -- Tom Karwin)

(Rosa mulliganii LS) This rose had an undetermined identity for several years, until Brian Mulligan, former curator of the Washington Park Arboretum, identified it as a native of China. (Contributed -- Tom Karwin)

(Philadelphus lewisii) Lewis’s Mock Orange is a valuable background shrub that grows well in full sun and partial shade. It grows best with little exposure to winds. (Contributed -- Tom Karwin)

(Rosa mulliganii CU) In addition to welcoming many bees, all ramblers provide good shelter, including potential nesting sites, for wild birds. (Contributed -- Tom Karwin)

My rambling rose has burst into bloom, on schedule.

All my other roses (mostly hybrid teas and climbers) have displayed their peak blooms and then gone through renewal pruning (deadheading). We now await repeat blooming in three or four weeks.

As promised, in this column I share the subsequent and remarkable abundance of my prized rambler, Rosa mulliganii, that produces great clusters of single white blooms in June, when it becomes the favorite of several different species of bees. This is demonstrated by a close-up photo of these blossoms; I am holding several other photos showing where bees had just left!

I came upon this rose several years ago at Cabrillo College’s Horticulture Department annual plant sale. I did not recognize the species, but the young plant seemed healthy and vigorous in a 2-gallon nursery pot, and I am easily attracted to an unfamiliar addition to the garden.

After I learned that this plant grows to impressive dimensions, I installed it next to a redwood fence with good exposure to sunlight. With help, I developed a trellis using vinyl-coated galvanized wire rope cable threaded through sturdy zinc-plated lag thread screw eye bolts with 6-inch shanks. The trellis has three horizontal cable strands that are twenty-four feet wide and held well away from the fence surface for air circulation.

The rose soon filled the trellis and then grew beyond it by sixteen feet in one direction, where there was limited sun exposure, and about eight feet in the other direction, where a tree created some shade. The overall width has reached 48 feet. I’m tempted to remove the trees to free the rose to pursue its ambitious goals.

This rose species is a feature of the highly regarded white garden at Sissinghurst Castle Garden in England, where it has been grown on the four sides of a large square trellis about 10 feet high.

Like other rambling roses, Rosa mulliganii blooms only once in June and should be pruned in late summer, after its show of flowers and hips. The Royal Horticultural Society’s pruning advice includes (1) thin and shorten excessive growth by removing entirely one-third of the oldest stems, (2) prune out all stems that have flowered and tie new ones in to take their place, and (3) shorten side shoots by about two-thirds. That project is on my calendar each year!

You might not have—or even want—a rambunctious rambling rose, but it’s always a good idea to research the cultivation and pruning of your plants, especially the unusual ones. Hybrid tea roses, which are popular garden subjects, need relatively familiar practices for good care, while climbers, miniatures, old garden roses, and of course ramblers will grow best with individualized care.

My survey of white flowers currently in bloom includes a Getty White Agapanthus (A. praecox ssp orientalis ‘Getty White’). This variety grows in the South African garden perennial garden bed, alongside the more familiar Dark Blue Agapanthus (A. africanus x pendulus ‘Storm Cloud’) and a light blue variety (A. praecox orientalis cultivar unknown) I tried but neglected an interesting blue-and-white bi-color cultivar (A. ‘Twister’) and should try it again.

Another white-flowering plant in bloom now is Lewis’ Mock-orange (Philadelphus lewisii), collected in 1806 by Meriwether Lewis, during his historic expedition through northwestern America with William Clark. This plant, a member of the Hydrangea plant family, grows vertically up to 9 feet and produces clusters of white, four-petaled flowers. The blossoms have “a heavy, sweet scent similar to orange blossoms with a hint of pineapple.” To manage this shrub’s shape, every few years cut one-quarter of the branches to the ground.

Selective placement of white flowers in the garden could add to the overall effect or complement the aesthetic contributions of flowers of other colors. Another option is to develop a bed of several different white flowering plants to feature an unusual-theme and comparisons of the subtle variations of white. For design ideas and plant lists for this thematic approach to a garden, search the internet for “white flowers.”

Tom Karwin is past president of Friends of the UC Santa Cruz Arboretum and the Monterey Bay Iris Society, a Lifetime Member of the Monterey Bay Area Cactus & Succulent Society, and a Lifetime UC Master Gardener (Certified 1999–2009). He is now a board member of the Santa Cruz Hostel Society, and active with the Pacific Horticultural Society. To view daily photos from his garden, https://www.facebook.com/ongardeningcom-566511763375123/. For garden coaching info and an archive of previous On Gardening columns, visit http://ongardening.com. https://cactusandsucculentsociety.org/. 

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