CONIFERS IN THE SOUT H: TIME TESTED SPECI ES AT THE BAKER ARBO RETUM
By Peggy McKillip and Mitchell Leichhardt
THE BAKER ARBORETUM IS LOCATED IN BOWLING GREEN, KENTUCKY AND IS
AFFILIATED WITH WESTERN KENTUCKY UNIVERSITY. IT WAS FOUNDED BY JERRY
BAKER IN THE EARLY ‘90’S.
FOR MORE INFORMATION, VISIT WKU.EDU/BAKERARBORETUM/INDEX.HTM
Like other arboreta and botanical gardens, one of the
goals of the Baker Arboretum is to explore the range of
plants that can be grown successfully. The challenge of
growing conifers in Western Kentucky requires that the
plants not only endure ice and snow, but specifically heat
and humidity. Over the years, we have noticed some
species that have performed with excellent results.
Bowing to curiosity, we culled our records to come up
with a list of some of the best that have survived and
thrived for at least 10 years. While many of these
species are well known to take a range of conditions, a
few surprised and delighted us.
USDA ZONE 6B/ AHS ZONE 7
AVERAGE ANNUAL RAINFALL:
49”
AVERAGE ANNUAL SNOWFALL:
3”
AVERAGE MAXIMUM
TEMPERATURE: 89° F
AVERAGE DAYS ≥95° F: 15,
≥100° F: 2.5.
AVERAGE MINIMUM
TEMPERATURE: 25° F
AVERAGE DAYS ≤10° F: 5
LIMESTONE ROCK OUTCROPS
ON A 6-20% SLOPE
PH RANGE OF 6.9-7.3
LIMITED WET OR BOGGY
AREAS
SITE CONDITIONS
The Baker Arboretum was built on a
ridge in rolling hills. The arboretum
has a large native Oak-Hickory canopy
with a significant presence of Ash, and
a predominantly Redbud understory.
The thin, clay-rich soil over rock, hilly
slopes and karst geology, creates challenges for
landscaping. The limestone bedrock is often porous with
numerous conduits and cavities and causes water to
drain quickly into the cave systems. Berms and terraces
are used to add amended soil to the thin natural layer,
and slow down water runoff. During the summer and
dry periods, a combination of sprinklers and drip
irrigation is used. Granulated sulfur is applied, according
to specific pH needs and soil test results.
The bedrock geology of the
arboretum consists of limestone,
either exposed as rocky outcrops,
or buried by a thin layer of
alkaline, clay-rich soil. Slopes vary
from 6-20%. This limestone forms
the geological foundation of the
"karst" landscape of Kentucky, a
landscape seen throughout the
Bowling Green area and other
Kentucky sites such as Mammoth
Cave National Park. Physical and
chemical interactions between the
limestone and flowing water lead
to the development of caves,
sinkholes, and other karst features
1
observed in these areas.
SELECTED FAVORITES:
The following species and cultivars were selected for reliability, beauty, adaptability and are
over 10 years old. Many are 20 years old. The cultural descriptions listed are our adapted
practices, specific to the local environment.
SIZES AT PLANTING ARE ESTIMATES. SIZES ARE LISTED HEIGHT X WIDTH.
CATEGORIES: WATER NEEDS: DRY, DRY TO MEDIUM, MEDIUM, MEDIUM TO WET AND WET.
SUN NEEDS: FULL SUN, FULL SUN TO PART SHADE, PART SHADE, PART SHADE TO FULL SHADE AND FULL SHADE.
**CANDLED OR PRUNED
Cedrus atlantica ‘Glauca Fastigiata‘
SIZE AT PLANTING
9’ x 3’
CURRENT SIZE
20’ x 4.5’
WATER
Dry
SUN
Full Sun
Cephalotaxus harringtonia ‘Prostrata’
SIZE AT PLANTING
1’ x 1.5’
CURRENT SIZE
3’ x 8’
WATER
Medium
SUN
Part Shade
Chamaecyparis obtusa ‘Nana Lutea’
SIZE AT PLANTING
3-4’ x 2’
CURRENT SIZE
6’ x 4.5’
WATER
Medium
SUN
Part Shade to Full
Shade
Chamaecyparis obtusa ‘Verdon’
SIZE AT PLANTING
3-4’ x 2’
CURRENT SIZE
8’ x 3’
WATER
Medium
SUN
Part Shade to Full
Shade
Larix decidua ‘Varied Directions’
SIZE AT PLANTING
2’ x 3’
CURRENT SIZE
**3.5’ x 24’
WATER
Medium
SUN
Full Sun to Part
Shade
Cedrus are predominantly large trees and are well
suited for the Kentucky environment. They require
minimal care and rarely need additional water.
Mitchell Leichhardt notes “that for many years Cedrus
were not considered hardy in the Bowling Green area.”
Glauca Fastigiata is an excellent columnar form for the
typical smaller urban landscape.
The ones planted in partial shade do best. Moderate
watering and minimal care is needed. During the recent
droughts, this species did not require any additional
watering. We have had 100% survival rates on this
underutilized genus. Prostrata has proven so reliable, that
more have been planted to add to the groundcover palate.
To accommodate for the summer heat and humidity, we
have found that C. obtusa prefer to be located in partial to
full shade. The species rarely requires additional care
besides even moisture and pH monitoring. This versatile
species is able to fit just about any landscape need due to the
numerous foliage shapes, colors and forms. Nana Lutea has
golden yellow highlights year-round, and provides the touch
of color for a dark spot.
Verdon is used in vignettes to contrast with rounded shapes
such as mounding Japanese Maples and conifer brooms. The
golden color varies by specimen, depending on original
source and shade in the planted location. Mitchell
Leichhardt has found both Verdon and Nana Lutea relatively
slow growing, unlikely to outgrow their companion plants
and useful for partially shaded sites.
This lovely species is underutilized in this area. We join in the
coniferite chorus in recommending Varied Directions. It can
be used as the solo groundcover, spreading almost 25 feet.
This one is planted next to a walkway, allowing children of all
ages to touch the soft foliage. During the summer and
droughts, moisture levels require additional monitoring.
Picea orientalis ‘Skylands’
SIZE AT PLANTING
7-8’ x 3’
CURRENT SIZE
20’ x 7’
WATER
Medium
SUN
Full Sun to Part
Shade
Pinus densiflora ‘Low Glow’
SIZE AT PLANTING
1.5’ x 2’
CURRENT SIZE
**3.5’ x 8’
WATER
Medium
SUN
Full Sun
Pinus flexilis ‘Vanderwolf's Pyramid’
SIZE AT PLANTING
10’ x 4’
CURRENT SIZE
25’ x 24’
WATER
Medium
SUN
Full Sun
Pinus thunbergii ‘Banshosho’
SIZE AT PLANTING
2’ x 3’
CURRENT SIZE
**3.5’ x 4’
WATER
Medium
SUN
Full Sun
Pinus thunbergii ‘Thunderhead’
SIZE AT PLANTING
3’ x 3’
CURRENT SIZE
**5’ x 6’
WATER
Medium
SUN
Full Sun
Taxus baccata ‘Stove Pipe’
SIZE AT PLANTING
8’ x 2’
CURRENT SIZE
16’ x 4’
WATER
Medium
SUN
Full Sun to Part
Shade
Tsuga canadensis ‘Fantana’
SIZE AT PLANTING
4.5 x 5’
CURRENT SIZE
6’ x 8’
WATER
Medium
SUN
Part Shade to Full
Shade
This species is one of the hardiest spruce species for
Kentucky. The Skylands at the arboretum is planted out in
full sun and is a great example of a narrow pyramid shape
that is so useful in smaller landscapes. At a distance, the
entire tree is a golden yellow, but observed up close show
that the needles are yellow on the top and green on the
underside.
P. densiflora and P. thunbergii have proven to be hardier
than P. mugo for the arboretum. Planted along a
meandering walk with other pine witches brooms, aptly
named Low Glow subtly glows among the darker green
brooms. This specimen is candled due to the proximity of the
walkway.
The large Vanderwolf's Pyramid, with blue green foliage and
pyramidal shape, is a good substitute for the oft used P.
strobus. Useful in the landscape as a single specimen and a
large screen. The species has minimal maintenance needs.
Both P. densiflora and P. thunbergii require little
maintenance. Staff and visitors consistently admire this
species. The lighter green Banshosho contrasts well with
deep green conifers. It is a moderately slow grower.
Candling allows it to be maintained on a site without
crowding for a number of years.
Like mounding clouds, the deep green Thunderhead
contrasts well with other specimens. Generally used as a
specimen, it can also be effective as an excellent medium
height buffer or screen. We are using single specimens
combined with other medium height shrubs to strategically
screen utility areas.
During the summer and droughts, moisture levels require
monitoring. Straight as a soldier, Stove Pipe is an ideal
columnar contrast with other conifers. Little or no pruning is
required to keep the columnar shape.
With evenly moist soil, Hemlocks have performed admirably.
While they do very well in part to full shade, they can be
planted in the full sun as long as the soil moisture is
monitored during dry spells. ‘Fantana’ is a charming
mounded form. It is slower growing than Sargentii.
HEALTHY SPECIES THAT ARE 10 YEARS OR OLDER.
*KENTUCKY NATIVE
Cedrus atlantica
Blue Atlas Cedar
Larix decidua
European Larch
Pinus sylvestris
Scots Pine
Cedrus deodara
Deodar Cedar
Picea abies
Norway Spruce
*Pinus taeda
Loblolly Pine
Cephalotaxus harringtonia
Japanese Plum Yew
Picea abies
Norway Spruce
*Pinus virginiana
Virginia Pine
Chamaecyparis obtusa
Hinoki Cypress
Picea asperata
Tapao Shan Spruce
Pinus thunbergii
Japanese Black Pine
Chamaecyparis pisifera
Sawara Cypress
Picea glauca
White Spruce
*Pinus virginiana
Virginia Pine
Cryptomeria japonica
Japanese Cedar
Picea mariana
Black Spruce
Pinus wallichiana
Himalayan Pine
Cupressus arizonica
Arizona Cedar
Picea omorika
Serbian Spruce
Platycladus orientalis
Chinese Arborvitae
Cupressus nootkatensis
Nootka Cypress
Picea orientalis
Oriental Spruce
Pseudotsuga menziesii
Douglas Fir
Ginkgo biloba
Ginkgo
Picea pungens
Colorado Spruce
*Taxodium distichum
Baldcypress
Juniperus rigida
Needle Juniper
Pinus densiflora
Japanese Red Pine
Taxus baccata
English Yew
Juniperus chinensis
Chinese Juniper
Pinus flexilis
Limber Pine
Taxus x media
Yew
Juniperus conferta
Shore Juniper
Pinus heldreichii
Bosnian Pine
*Thuja occidentalis
Eastern Arborvitae
Juniperus davurica
Dahurian Juniper
Pinus mugo
Mugo Pine
Thuja plicata
Western Red Cedar
Juniperus horizontalis
Creeping Juniper
Pinus nigra
Austrian Pine
Thujopsis dolabrata
Hiba Arborvitae
Juniperus squamata
Flaky Juniper
Pinus parviflora
Japanese White Pine
*Tsuga canadensis
Canadian Hemlock
*Juniperus virginiana
Eastern Red Cedar
Pinus resinosa
Red Pine
Tsuga diversifolia
Japanese Hemlock
(syn. Chamaecyparis)
Contributors: Peggy McKillip is a native of Athens, Georgia, and earned her B.S. in Horticulture at the University of
Georgia. She has been the Accessions Horticulturist for the Baker Arboretum for six years.
Mitchell Leichhardt is a native of Bowling Green and degreed from Western Kentucky University. He served as past
president of the Kentucky Nursery and Landscape Association. He has been growing and observing plants as a local
nurseryman and landscape architect for over 65 years.
1
Fred Siewers, Ph.D. Professor of Geology, Western Kentucky University.