A member of the Myrtaceae family, Callistemon derives from the Greek kallos which stands for beauty, and stemon which stands for stamens. Whether grown as an open shrub or small tree, the plant aptly deserves its name as the bottlebrush bush. This Australian native sports (OK, let’s say it shouts) red inflorescences with the stamens making the show. At SFA Gardens, our best specimen is parked against a hot, sunny southwest-facing wall.
The RHS lists some 25 species of low shrubs and trees in the genus and easy interspecific hybridization has led to some confusion in “what is what” in the Callistemon world. Dirr lists six species and comments on the difficulties in taxonomy and identification. In a December, 1999 communication, Valerie Tyson at the JCR Arboretum noted that there had been eight accession groups of seed or plants there, with only a few survivors still present in that Zone 7 landscape. Of course, there are tropical bottlebrush hybrids and selections that are worthy of any garden landscape that can grow them, and they should be used more in those climes that allow it. In our Zone 8 challenge (with a December 23 1989 zero degrees Fahrenheit event bench mark), our main problem is hardiness. The Arboretum is home to a couple of other species but we are still waiting for some single digit freeze information that’s not in yet.
We have one Callistemon that survived that 1989 benchmark, Callistemon linearis, or narrow-leaved bottlebrush. It’s hardy in Zone 8 and into Zone 7 with some protection. The picture is of our clone “Hannah Rae’ parked against the South face of the big metal-sided Art building on the SFASU campus. The specimen is an 8’ open shrub, a sparsely-branched sprawling accent piece – with nearby neighbors of other dry-loving xericscape shrubs: cacti, Hesperaloes, Agaves, Yuccas, Dasylirions, desert shrubs and perennials. The plant has thrived on a hot western face of this metal building for 10+ years in one of our almost-never-irrigated locations of the dry garden. It has never failed to produce an outstanding color show. Callistemon ‘Woodlanders Red’ looks strong. C. ‘Little John’ is a dwarf that we have lost before but is once again fully entrenched in the garden. With fine form and a shape, this variety needs full sun and a very well drained location.
C. sieberi, the alpine bottlebrush, was in the Arboretum but was lost to drought as a young plant; it is reported to be the most cold-hardy. C. brachyandrus, the prickly bottlebrush, has been with us many years but has yet to be tested by a winter with single digits. At any rate, there are plenty of opportunities to move the positive characteristics of many “tropical” bottlebrushes (bloom size and color, primarily), into the genetics of the most cold hard types.
In the landscape, bottlebrush can best be used in any number of ways. As part of a mixed border, as a specimen, or as a South-facing wall accent piece, bottlebrush makes its mark when in bloom. The plant’s natural tendency to be an open, sparsely-branched shrub can be subdue a bit by pruning after bloom to force branching and create a denser nature to the plant. In full western sun, the plant will respond. While the plant’s natural nature is to inhabit the streambanks and creek banks of Australia, the species is extremely drought resistant once well established in the landscape (two to three years).
Propagation by seed is reported as easy. We’ve never tried. Opportunities for finding hardy forms through seedling selection seems reasonable. June cuttings under mist have been successful and once roots appear the cuttings should be quickly moved from the mist bed.