Plant of the Month for March 2010

Penstemon cardwellii 'Roseus'; photo by Todd Boland
Penstemon cardwellii 'Roseus'

Description and general information

This penstemon belongs to the Dasystemon group, most which form evergreen subshrubs. The wild species of P. cardwellii, which has purplish-blue flowers, hails from Washington and Oregon. The cultivar 'Roseus' appears more commonly in cultivation.

This cultivar forms a mat 10-30 cm (4-12") tall. The foliage is a lovely grey-green to blue-green colour.


This penstemon, like most, prefers well-drained soil and a sunny site. Like the Dasystemon group in general, this species can tolerate considerable winter-wet so is more suitable in wetter climates than most penstemons. It is known to be hardy in zone 4. If snow cover is not reliable, position them in a sheltered site as cold winds can dessicate the plants. They do not appear to be fussy about soil pH.

Bloom period

Late spring to early summer.


Seed, cuttings


Surface sow seeds in the fall and leave outside in a cold frame or if sown inside, provide them with 8 weeks stratification.


Essentially division will result in the plant falling apart into separate 'cuttings' which can be stuck and rooted.


Cuttings root easily anytime after flowering; they will root within a matter of weeks; keep them lightly shaded during this period.

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