Plant of the Month (August) : Dunn’s lobelia

Dunn's lobelia (Lobelia dunnii var. serrata) - Mother Nature's Backyard

By
August, the only perennials blooming in Mother Nature’s Backyard (other than
the buckwheats) are those in moist, shady places. One pretty little perennial, blooming for the
first time this year, is the Dunn’s lobelia. The scientific name is pronounced low-BEE-lee-uh DUN-ee-eye
sir-RAY-tuh.

Dunn’s
lobelia (sometimes also called Blue lobelia and Rothrock’s lobelia) is a
California member of the Campanulaceae, the
Bellflower family. This family has 80+
genera and about 2400 species worldwide, mostly in the Northern Hemisphere [1]. Included are garden favorites like the Campanulas
and the Lobelias. As suggested by the
common name, the flowers of the Campanulaceae are
bell-shaped and often blue or violet colored.

The genus Lobelia
is well-known to gardeners. Ornamental cultivars spread their old-fashioned
charm under trees and along shady pathways.
They take a little extra water, and so are useful for naturally moist
areas. While some are annuals (or
treated that way), perennial species have the added advantage of coming back,
year after year, in a welcome splash of green and blue. No wonder gardeners like the Lobelias.

Only two Lobelia species are California natives. Both Lobelia
cardinalis and Lobelia dunnii are
native to the mountains of Central (Santa Barbara and Ventura Counties) and Southern
California. They also grow along the Monterrey County coast. Where ever they are found, they favor shady,
moist areas: canyons, seeps, rocky stream banks, the edges of waterfalls – you get
the picture.

There is current debate about the proper taxonomic
status of Lobelia dunnii. Some have proposed reverting to an older
taxon, Palmerella debilis, first proposed by the eminent 19^th
century taxonomist Asa Gray [2]. The California Lobelias do have a
distinctive appearance, and may well deserve a genus of their own. But since most native plant and garden folks
know Dunn’s lobelia as Lobelia dunii, we’ll stick with that name for
now.

Lobelia
dunnii var. serrata, the variety we’ve got in the garden, can still be found
in the canyons of the San Gabriel and San Bernardino Ranges, as well as on
Santa Catalina Island and in northern Baja California, Mexico. It was first collected in the 1800’s and grows
in moist places in Coastal Sage Scrub and Chaparral below about 4500 ft. (1400
m.). If you hike the moist canyons below
San Antonio (Mt. Baldy) and Ontario Peaks in the San Gabriels, you may have
seen it along the streams.

Dunn's lobelia (Lobelia dunnii var. serrata) - in Spring

Like most local perennials, Dunn’s lobelia dies
back to the ground in fall, to emerge again with the winter-spring rains. If
you continue to water it, the plant will remain green into early fall – then let
it dry out and rest. Most S. California
perennials really do need a period of rest in the fall.

Dunn's lobelia (Lobelia dunnii var. serrate): young leaves

If you don’t know what you’re looking for, you may
miss the emerging stems (see above). The
emerging leaves look quite different from the leaves of the mature, summer
plant. If a plant is happy, it will send
up more sprouts each year, and spreading to a 2-3 ft. patch. Plants also re-seed in local gardens.

Dunn's lobelia (Lobelia dunnii var. serrate) - foliage

Dunn’s lobelia is an herbaceous perennial, growing
at most 12-18 inches (30-45 cm.) tall. It is sometimes erect, but as likely to be
somewhat sprawling (decumbent) of habit.
The leaves are a fresh spring green, elongated and becoming slightly smaller
up the stems. The foliage is quite open; not shrubby, but rather a delicate,
lacy groundcover, somewhat mint-like in appearance.

Dunn's lobelia (Lobelia dunnii var. serrata) - flowering stem

The flowers are cottage garden pretty – small and
pale lavender or blue. The flowers may be up to 1 inch (2.5 cm) long. They are clustered at the tops of the stalks. As
flowers open over time, the total bloom season may be a month or more.

The petals are fused into a long tube, with 5
lips. The lower three lips are elongated
and extend down. The upper two lobes are
curled tightly back – a unique appearance (see below). The flowers are loved by long-tongued butterflies;
this plant is often planted specifically to attract them.

Dunn's lobelia (Lobelia dunnii var. serrata) - close-up of flowers

Dunn’s lobelia will grow in most local soils
(except salty or alkali), though it prefers a rich loam. It does fine in our local clays. We’ve been most successful growing this plant
on the north side of a tall wall. It
would also do well in dappled sun under trees.
We’d only try it in fall sun at the edges of a pond.

Dunn's lobelia (Lobelia dunnii var. serrata) - delicate perennial

This is a species that likes moist soils - it can
even take winter flooding. Regular water
through the bloom season is probably best.
We give ours (in clay) a deep soaking every 3 weeks in summer, then
taper off in early September. That’s really about it.

Lobelia dunnii is a perennial to tuck into shady, moist
places. It does well with native
grasses, sedges, juncus, Solanum, Nicotiana and others that like a little extra
water. We’d love to try it in a moist
pot on a shady porch. It’s not a garden diva.
But it’s charming as a violet is – simple, sweet and unassuming. And then there are the butterflies!

In
summary, Dunn’s lobelia is a wonderful little perennial. If you have a moist shady spot – or can
create one – this might be a butterfly plant to try.