University of Vermont Extension
Department of Plant and Soil Science
Dr. Leonard Perry, Extension
University of Vermont
Garden phlox are one of the staples of the
summer perennial garden with their large flower clusters in many colors, and
have been used in gardens since Colonial times.
They’re native to many parts of the eastern U.S., are long-lived, low
maintenance, and provide color in late summer when many other perennials have
finished bloom. There are many choices,
with some having good resistance to the white powdery mildew disease.
comes from the Greek word for flame, referring to the brightly-colored
flowers. The main species (paniculata) of most cultivars
(cultivated varieties) refers to the dense, flower clusters or panicles on tops
of the stems. Although these can
sometimes be heavy and cause stems to droop a bit, usually stems are sturdy and
upright. Another species (maculata)—the early or meadow phlox—has
more elongated and cylindrical flower clusters.
A hybrid (x arendsii) between
the garden phlox and the blue phlox (divaricata)
has good mildew resistance. You may see
all these species referred to collectively as “border phlox”.
phlox are in the phlox family—the Polemoniaceae—just as is the Jacob’s Ladder (Polemonium). They combine well with bee balm (Monarda), Joe-Pye (Eupatorium), ornamental grasses such as the switchgrasses (Panicum), daylilies, rudbeckia, Shasta
daisies, and meadowsweets (Filipenula). They make good cut flowers, and in fact some
of the newest cultivars (the Feelings series from Holland in particular) were
bred for this purpose.
grow and bloom best in full sun to part shade—6 hours or more of sun a
day. They prefer moist, well-drained
soils but will tolerate some drought once established. Although listed
as hardy in USDA zones 4 to 8 (to -30 degrees F in
winter), they prefer cooler nights as in the north. “Deadhead” or pick flowers off once bloom is
finished to improve appearance, and to keep them from seeding around the
garden. Plants won’t come true from
seeds. They seldom need division unless
too large, or blooms get smaller and fewer.
early summer, you can cut plants back by about one-quarter to one-third, which
will promote branching and even later bloom.
I learned this trick from the deer, which love to graze the tender
shoots. If you want phlox to bloom in
summer rather than fall, and have deer about, you may need to consider some
form of deer repellents or fencing.
the only problems of this perennial are spider mites and powdery mildew. The mites are very small, so you’ll likely
need a hand lens to find them on the undersides of leaves. What you can see is the stippled yellowish
leaves, which are puckered and very yellow when severe. They’re more of a problem in hot, dry
weather, and can be controlled with both organic and synthetic sprays—just make
sure to get the undersides of leaves, and to apply according to label
mildew is an appropriately named fungal disease, often a problem in humid
conditions and with poor air movement.
It is more a problem in some areas than others, some years than others,
and with some cultivars than others.
Although there are sprays for this, and providing good spacing with good
air movement can help reduce this, selecting resistant cultivars is perhaps
trials in Chicago, three quarters of the cultivars were impacted in some
years by powdery mildew. Those with the
greatest resistance in all years included ‘Sherbert Cocktail’, ‘Flower Power’, ‘Becky
Towe’, ‘Frosted Elegance’, ‘Goldmine’, ‘Natural Feelings’, ‘Peppermint Twist’,
‘Rubymine’, and ‘Shortwood’.
‘Shortwood’ was the top cultivar in all respects in these trials, the only one
in fact to receive a five-star excellent rating. With its rosy-pink flowers, similar to the
species, it is taller than many of the newer selections bred for a more compact
habit. Its name is deceiving, as it
reaches 4-feet or more tall, being named instead for the garden of plant expert
and garden writer Stephanie Cohen. It
originated as a seedling of the white-flowered ‘David’, discovered in
Pennsylvania by grower and breeder Sinclair Adam, Jr.
is arguably the most popular white-flowered cultivar, and although in previous
Chicago trials was listed as fair for mildew resistance, often gets no mildew
in other areas. It was selected by the
Perennial Plant Association as Perennial of the Year for 2002. ‘David’ was discovered as a seedling in a native
population at the Brandywine Conservancy in Pennsylvania, and the above grower
was instrumental in its introduction.
The garden phlox ‘Katherine’ rated good for mildew resistance in these
trials. It has lavender flowers with a
white central “eye”.
phlox have solid color flowers, mainly pink, but also many in purples, with
some red, lavender, white, and even blue.
Others have this central contrasting eye of a different color. Some of the top-rated phlox with such flowers
include ‘Orange Perfection’ which is orange with magenta eye, ‘Norah Leigh’
which is pale pink with darker eye, ‘Little Boy’ which blooms violet purple
with white eye, ‘Frosted Elegance’ blooming pale pink with darker eye, ‘Delta
Snow’ which is white with purple eye, and ‘Miss Karen’ which blooms bright pink
with darker eye.
more unusual flowers there is ‘Peppermint Twist’ with pink and white stripes
like a peppermint. ‘Sherbert Cocktail’
opens pink, but turns white with a pink blush and yellow tips to the
petals. The Feelings series, such as the
deep pink ‘Fancy Feelings’, has straplike petals if any, other flower parts
such as sepals being what you see instead.
Perhaps the most unusual is ‘Blue Paradise’, whose violet flowers start
as blue buds, and then fade to blue.
most phlox have green leaves, some are variegated with creamy white
margins. ‘Norah Leigh’ has wider
variegation than ‘Crème de Menthe’ or ‘Frosted Elegance’. ‘Goldmine’ has broader golden to creamy
variegation than ‘Giltmine’. While
‘Rubymine’ has purplish highlights to its creamy variegation, reddish
highlights are on the yellow-rimmed leaves of ‘Becky Towe’ and cream-variegated
‘Harlequin’. Unfortunately, as with many
perennials, the variegation often is not stable. Over a few years, most or all leaves may
revert to green.
more on all the 75 cultivars, including the 27 top-rated, in the trials
Chicago Botanic Gardens is online
(www.chicagobotanic.org/research/plant_evaluation/#notes). One of the
more extensive sources of phlox,
both for information and ordering online, is Perennial Pleasures Nursery
Vermont (perennialpleasures.net). Grower
and manager Rachel Kane specializes in garden phlox, having 137
with other heirloom perennials. If in
Vermont in early August, make sure to check out her Phlox Fest.