Propagating Bitterbrush Twigs for
Restoring Shrublands
V. M. Kituku
W. A. Laycock
J. Powell
A. A. Beetle
native for bitterbrush establishment may be propagation
from stem cuttings (Nord 1959).
However, no study has reported success of propagated
stems upon transplantation and survival once plants are
subjected to winter conditions. Guidelines on soil chemical
composition necessary for continuous growth of the transplanted plants is also missing. Therefore, the objective of
this study was to determine methods of enhancing bitterbrush stem propagation, winter survival, and transplantation success.
Abstract—There was no significant difference in rooting success
between bitterbrush (Purshia tridentata Pursh) plants from 7 different locations in southcentral Wyoming. Over 60% of all plants
had roots at least 2 cm in length 45 to 60 days following propagation. Transplantation from propagation media to containers had
no major negative impact on the plants, based on the 85% survival
of all transplanted plants. When plants were subjected to artificial winter conditions of –25 °C, 2 hrs/day for 2 weeks, about 50%
survived and resumed growth in the spring. The morphological
development that followed exposure to winter conditions suggests
propagation by cutting and outplanting prior to winter is a feasible
method of preparing containerized bitterbrush plants for field
planting.
Methods
During the spring of 1989, bitterbrush populations representative of distinct geographical ranges, elevations, vegetation types, plant morphology, and soil factors were selected in 7 areas within southcentral Wyoming. From each
population, 10 mature, vigorously growing plants were selected, and 10 current growth, unbrowsed twigs (total of
100/population), at least 10 cm long, were cut with a heel
of last growth in late June 1989. Heels from older wood
facilitate leader growth (Nord 1959). At this time, the twigs
were capable of withstanding water and nutrient shortage
and propagating under a conducive environment. The twigs
were put in a cooler containing ice to avoid excessive loss
of water.
Propagation procedures followed those recommended by
Nord (1959). Heels were moistened with water, and dipped
in a common rooting hormone preparation containing 0.3%
indol-3-butyric (IBA) acid in talc. Stem origin was labeled
on a plastic board. Cuttings were randomly planted 2 to
4 cm deep in propagating flats at a greenhouse in Laramie.
The rooting medium had equal amounts of sand, sponge
rock and vermiculite with a pH of 7.0. To avoid or minimize root disease, a fungicide was applied to the soil. The
chemical composition of the soil used is shown in Table 1.
Temperature was maintained at 20 to 25 °C, and plants
were watered daily until roots developed after 45 to 60 days.
Cuttings were transplanted to labeled containers in midAugust and grown for 5 months with 3 watering days/week
before they were gradually introduced to winter conditions.
In February, the plants were subjected to 8 hours of daylight at 2.2 °C, and watered once a week for 30 days. Plants
were put in a freezer at –25 °C, 2 hours/day for 2 weeks before returning them to 2.2 °C, 8 hours of daylight for 2 weeks.
From April to June, plants were grown at 20-25 °C, watered
twice a week, and kept in weed free conditions.
The increasing demands on rangelands for forage necessitate development of cost-effective and efficient methods of
increasing forage productivity. Bitterbrush possesses most
of the qualities of a desirable browse plant, and diminishing
quantities of bitterbrush within its range has prompted
substantial restoration efforts (Nord 1965, Nord et al. 1967).
However, increasing bitterbrush production through seeding has been only minimally successful.
For example, Nord (1959) states, “seed production in bitterbrush, an ice cream plant on western ranges, is erratic
and unpredictable. Even well-filled seed may be worthless
or at best produce seedlings unable to survive under natural conditions.” Hubbard (1964) amplified the dilemma by
noting that “successful seeding isn’t cheap.” However, when
justifying the economics of a bitterbrush seeding project,
he posed the question of what is more expensive: to let deteriorated ranges alone or to restore them.
Failure or minimal success in bitterbrush restoration
has been associated with rodents, jackrabbits, grazing ungulates, and insects (Hubbard 1964). Because of the limited success in reseeding bitterbrush, a more viable alter-
In: Roundy, Bruce A.; McArthur, E. Durant; Haley, Jennifer S.; Mann,
David K., comps. 1995. Proceedings: wildland shrub and arid land restoration symposium; 1993 October 19-21; Las Vegas, NV. Gen. Tech. Rep.
INT-GTR-315. Ogden, UT: U.S. Department of Agriculture, Forest Service,
Intermountain Research Station.
V. M. Kituku is Riparian Ecologist, Idaho Power, P.O. Box 70, Boise, ID
83707; W. A. Laycock, J. Powell, and A. A. Beetle are Professors of Range
Management, Department of Range Management, University of Wyoming,
Laramie, WY 82071.
327
Table 1—Characteristics of the soil used after propagation.
rooting success with 0.1% of indol-3-butyric acid compared
to 0.3%. Transplantation from propagation media to containers had no major negative impact on the plants, based
on the 85% survival of all transplanted plants.
By February, when bitterbrush plants would have lost
their leaves in the field, about 40% of the plants had green
leaves. Also a living plant could not be differentiated from
a dead one easily in those plants with no leaves. Thus, no
estimate on the actual number of living plants was obtained
before artificial wintering. However, all plants were subjected to artificial winter condition. About 50% survived
and resumed growth in the spring. Higher survival may
be possible with a less rigorous wintering process. Two
months after the wintering process (June), the regrowth
height ranged from 20 to 26 cm with a mean of 23.1 ± 6.1 cm;
overall leaf length ranged from 13.6 to 19.7 mm with a mean
of 16.2 ± 2.0 mm; leaf width (based on widest part) ranged
from 7.0 to 9.6 mm with a mean of 8.3 ± 1.6 mm. The morphological development that followed exposure to winter
conditions suggests propagation by cutting and outplanting
prior to winter is a feasible method of preparing containerized bitterbrush plants for field planting.
Chemical Composition
Total nitrogen (NO3N; ppm)
Avail. phosphorus (PO4P; ppm)
Potassium (K; ppm)
Iron (Fe; ppm)
Zinc (Zn; ppm)
Organic matter (OM; %)
pH
Electrical conductivity (ds/m)
18.5
12.0
331.0
4.1
4.6
2.6
7.5
1.5
Texture
Sand (85%); silt (10%); clay (5%)
Soluble Cations
Sodium (Na; meq/l)
Calcium (Ca; meq/l)
Potassium (K; meq/l)
Magnesium (Mg; meq/l)
2.1
19.1
1.2
2.1
Extractable Cations
Sodium (Na; meq/100g)
Calcium (Ca; meq/100g)
Potassium (K; meq/100g)
Magnesium (Mg; meq/100g)
Cation Exch. Cap. (meq/100g)
0.5
20.7
<0.1
0.7
References
7.4
Hubbard, R.L. 1964. A guide to bitterbrush seeding in
California. USDA For. Serv. PSW Exp. Sta. and Calif.
Dep. Fish Game Resour. 30 p.
Nord, E.C. 1959. Bitterbrush plants can be propagated
from stem cuttings. USDA For. Serv. Rep. PSW-149. 4 p.
Nord, E.C. 1965. Autecology of bitterbrush in California.
Ecol. Monogr. 35:307-334.
Nord, E.C., E.R. Schneegas, and H. Graham. 1967. Bitterbrush seed collecting by machine or by hand? J. Range
Manage. 20:99-103.
Results and Discussion
There was no significant difference in rooting success
between plants from different locations. Over 60% of all
plants had roots at least 2 cm in length 45 to 60 days following propagation. This rooting success was about twice
that achieved by Nord (1959) using 9 cuttings as opposed
to the 700 used in this study. Nord (1959) reported better
328