Green Roofs - Living Architecture Monitor - Winter 2019 - 8

PLANT PROFILE

THE WONDERS OF
DALEA PURPUREA

BY PROFESSOR BRADLEY ROWE, MICHIGAN STATE UNIVERSITY, EAST LANSING

Dalea purpurea (syn. Petalostemon purpureum)
(purple prairie clover) is a herbaceous perennial
native to most of North America within USDA
hardiness zones 3 to 8 except for parts of the east and
west coasts. It is widespread in the grasslands of the
Great Plains. Although its common name suggests
that it is a true clover (genus Trifolium), it is actually
a member of the plant family Fabaceae (bean family).
Because it is in the bean family, the plant is able
to fix nitrogen in the soil. The plant also has some
medicinal uses, its flowers attract butterflies, and it
has no serious insect or disease problems.

T

he species requires full sun and typically grows 30 to 90 cm (1
to 3 ft) tall with a spread of 30 to 45 cm (1 to 1.5 ft). Depending on the year, it flowers during June to August and features
numerous small showy purple flowers arranged on spikes up to
5 cm (2 in) long located at the end of the branches. The compound
leaves are 1 to 4 cm (0.4 to 1.6 in) long with 3 to 7 narrow leaflets
within each leaf. When mature, the plant has a coarse long taproot
that can reach 1.7 to 2.0 m (5.5 to 6.5 ft) deep.
In its natural environment, Dalea purpurea grows well in sandy,
well drained soils and gets much of its drought tolerance from the
aforementioned deep taproot. Thus, one would assume that it may
not do well on a shallow green roof. However, data collected in
green roof plant evaluations doesn't support that assumption.
Dalea purpurea as well as Dalea candida and Dalea villosa
were all trialed at the Chicago Botanic Garden (Hawke, 2015,
Chicago Botanic Garden Plant Evaluation Notes, Issue 38).

LIVING ARCHITECTURE MONITOR / WINTER 2019 / 8

Dalea purpurea was tested at
substrate depths of 10, 15, and
20 cm (4, 6, and 8 in) and given
an overall good performance
rating of 4 stars (out of 5) for
strong performance at all three
depths. However, the plants
exhibited larger flowers when
grown in 20 cm compared to
10 cm with an average flowers
size of 5 cm (2 in) compared to
3.8 cm (1.5 in). Plants in the
deeper substrate also flowered
earlier and for a longer period
of time. Regardless, they all established quickly and remained

DALEA PURPUREA IN FULL BLOOM
ON AN EXTENSIVE GREEN ROOF

vigorous through the five
year trial period. Plots were,
however, watered regularly
during the first year to ensure
establishment and then during
extreme drought periods in
subsequent years.
In a plant evaluation study
at MSU to measure long-term
performance that began
during May 2013, eighteen
roof platform sections were
filled to a substrate depth
of 10 cm and seeded with a
mix of native perennials and
grasses. In addition to Dalea
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Green Roofs - Living Architecture Monitor - Winter 2019

Table of Contents for the Digital Edition of Green Roofs - Living Architecture Monitor - Winter 2019

Table of Contents
Green Roofs - Living Architecture Monitor - Winter 2019 - IP
Green Roofs - Living Architecture Monitor - Winter 2019 - Cover1
Green Roofs - Living Architecture Monitor - Winter 2019 - Cover2
Green Roofs - Living Architecture Monitor - Winter 2019 - Table of Contents
Green Roofs - Living Architecture Monitor - Winter 2019 - AD1
Green Roofs - Living Architecture Monitor - Winter 2019 - 1
Green Roofs - Living Architecture Monitor - Winter 2019 - 2
Green Roofs - Living Architecture Monitor - Winter 2019 - 3
Green Roofs - Living Architecture Monitor - Winter 2019 - 4
Green Roofs - Living Architecture Monitor - Winter 2019 - 5
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Green Roofs - Living Architecture Monitor - Winter 2019 - 8
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Green Roofs - Living Architecture Monitor - Winter 2019 - Cover3
Green Roofs - Living Architecture Monitor - Winter 2019 - Cover4
Green Roofs - Living Architecture Monitor - Winter 2019 - 42
Green Roofs - Living Architecture Monitor - Winter 2019 - 43
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https://www.nxtbook.com/dawson/greenroofs/lam_2017fall
https://www.nxtbook.com/dawson/greenroofs/lam_2017summer
https://www.nxtbook.com/dawson/greenroofs/lam_2017Spring
https://www.nxtbook.com/dawson/greenroofs/lam_2016winter
https://www.nxtbook.com/dawson/greenroofs/lam_2016fall
https://www.nxtbook.com/dawson/greenroofs/lam_2016summer
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https://www.nxtbook.com/dawson/greenroofs/lam_2014fall
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https://www.nxtbook.com/dawson/greenroofs/lam_2014spring
https://www.nxtbook.com/dawson/greenroofs/lam_2013winter
https://www.nxtbook.com/dawson/greenroofs/lam_2013fall
https://www.nxtbook.com/dawson/greenroofs/lam_2013summer
https://www.nxtbook.com/dawson/greenroofs/lam_2013spring
https://www.nxtbook.com/dawson/greenroofs/lam_2012fall
https://www.nxtbook.com/dawson/greenroofs/lam_2012summer
https://www.nxtbook.com/dawson/greenroofs/lam_2012spring
https://www.nxtbook.com/dawson/greenroofs/lam_2012winter
https://www.nxtbook.com/dawson/greenroofs/lam_2011fall
https://www.nxtbook.com/dawson/greenroofs/lam_2011summer
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https://www.nxtbook.com/dawson/greenroofs/lam_2011winter
https://www.nxtbook.com/dawson/greenroofs/lam_2010fall
https://www.nxtbook.com/dawson/greenroofs/lam_2010summer
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https://www.nxtbook.com/dawson/greenroofs/lam_2009fall
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