The World Foliage Plant Industry - Acta Horticulturae

CULTIVATION
Taxus spp. grow in a wide range of cultural
conditions but thrive best on loamy soils of a
slightly acidic or neutral pH having adequate
moisture. According to Dirr (1990), good soil
drainage is critical for yews and anything less
than excellent drainage results in marked
reductions in growth or eventual death of the
plants. In poorly drained soils, root rot can be a
problem (Taylor et al., 1996). Yews will flourish
in open sun or partial shade, but should be
kept out of sweeping, desiccating winds, and
generally do not tolerate extreme cold or heat
well. Depending on the species, yews grow in
most hardiness zones, ranging from USDA zone
2 (T. canadensis) to zone 8 (T. floridiana) (Dirr,
1990; Gilman and Watson, 1993; Taylor et al.,
1996). Since many of the cultivars have a compact
and symmetrical form, little corrective pruning
is required. Dirr (1990) recommends pruning
rather than shearing to retain the natural
shape and habit of the particular yew cultivar,
although Taxus spp. can be sheared or pruned
severely into topiary forms. The size and shape
of the ornamental Taxus spp. varies greatly, ranging
from the upright tree form of T. baccata
‘Fastigiata’ (Irish yew) (Fig. 5) to the low spreading
cultivars of T. xmedia (‘Densiformis’,
‘Chadwickii’) (Fig. 6), attributes that have led to
the wide use of Taxus in the landscape (Dirr,
1990).
Figure 6. Taxus xmedia ‘Densiformis’: dense, low and shrub-like. Permission for use granted by
Waynesboro Nurseries, Waynesboro, VA.
Figure 5. Taxus baccata ‘Fastigiata’ - Irish
yew: rigidly upright branches. Permission
for use granted by Buckingham Nurseries,
Buckingham, UK.
Woody ornamental or Christmas tree fertilizer
guidelines can be used for Taxus spp.
Application of fertilizers having N, P (as P 2 O 5 ), K
(as K 2 O) ratios of 4:1:1, 3:1:1, or 3:1:2 are
recommended and can be top-dressed around
the base of the shrub’s drip line in the early
spring for established plants. An N only fertilizer
can be applied if there are adequate levels of P
and K, or slow release fertilizers can also be
used. Organic materials such as compost and
manure can also be utilized and will improve
soil structure; however, nutrient levels are often
variable and should be determined through
laboratory analysis. During site preparation just
prior to planting, incorporate P and K if tests
show deficiency, and leave N application for the
next year or use compost or well-rotted manure
to avoid root burning. Split applications of N
fertilizer during the growing season will reduce
the likelihood of root burn and will lessen the
potential for ground water contamination. Lime
applied at the time of planting will help correct
low soil pH and should be thoroughly mixed
with the soil in the root zone area. (Kujawski
and Ryan, 2000).
Although yews are resistant to many pests and
diseases, the Taxus mealybug (Dysmicoccus wistariae),
the Taxus scale (Pulvinaria floccifera), the
yew-gall midge (Taxomyia taxi), the black vine
weevil (Otiorhynchus sulcatus) and nematodes
(Pratylenchus spp.) have been known to cause
plant damage (Gilman and Watson, 1993;
Taylor et al., 1996).
THE DISCOVERY OF TAXOL ®
Taxol ® is likely the most well known chemotherapeutic
agent in medical history, which is ironic
as Taxus spp. have garnered little other modern
interest except as landscape plants. The discovery
of Taxol ® [generic name: paclitaxel] as a
unique anti-cancer compound occurred in the
early 1960s following a screening program initiated
by the National Cancer Institute (NCI),
which emphasized discovery of new plantbased,
anti-tumor agents (Stephenson, 2002).
Arthur Barclay, a botanist at the United States
Department of Agriculture (USDA), and three
student assistants collected 650 plant samples
in California, Washington and Oregon, which
included the bark, twigs, leaves and fruit of the
Pacific yew tree (T. brevifolia) (Wall and Wani,
1995; Patel, 1998). Although the yew samples
showed only modest anti-tumor activity initially,
later testing using different bioassay standards
resulted in paclitaxel being selected for further
development. Formidable chemical and sociological
obstacles were encountered as this promising
raw resource was moved along the drug
development path, including: paclitaxel’s water
insolubility; minute paclitaxel tissue concentrations;
and the requirement to harvest yew bark
at the cost of destroying the tree. The latter
issue resulted in confrontation between those
that desired to harvest the species for drug
development and conservation groups who
wanted the seemingly relentless destructive
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