The crown-of-thorns (Euphorbia milii) has long been
a staple crop of nursery-growers in the sub -
tropics & tropics, although its use in South Florida
landscapes has declined over the past few years.
There is, however, reason for renewed interest in this
plant because of recent emphasis on water
conservation and low maintenance.
In addition, the recent development of more attractive,
compact cultivars in a wide range of colors gives
landscapers an ideal subject for sites requiring a salt-
& drought-tolerant groundcover.
The genus Euphorbia is in the spurge family
(Euphorbiaceae) and includes some 2000 species of
diverse plants from annuals to trees. The poinsettia,
E. pulcherrima, is probably the most familiar species.
DESCRIPTION.
E. milii, a native to Madagascar, is a succulent, with
thick, fleshy stems adapted for water storage. The
stems are 5-7 sided, greyish-brown, branched & up to
2-3' in height, with many prominent, grey 1" spines.
The leaves tend to be obovate (wider near the tip), up
to 1½” long, but much larger (to 6") in the Thai
hybrids. They are spirally arranged, have smooth
margins, & vary from bright green to grey-green.
Foliage is present only on new growth. E. milii var
splendens is similar, but grows to 5-6'.
The inflorescence is composed of a specialized
structure termed a cyathium comprising a cup-like
involucre, within which is set a single much reduced
female flower surrounded by three male flowers
reduced to single stamens. The cyathia are borne in
clusters (cymes) and each cyathium is subtended by
two colorful bracts. These are termed cyathophylls,
and both red and yellow (in E. milii var lutea) occur
naturally. Plants are in flower year round, but are at
their best in dry, sunny weather (Winter & Spring).
As with other euphorbs, E. milii produces copious
quantities of poisonous, milky sap that can cause skin
irritation, & contains tumor promoting chemicals
(diterpene esters). The spines should be sufficient
warning to handle with care.
PROPAGATION.
Cuttings. Crown-of-thorns is usually propagated
from tip cuttings. Remove 3" stem tips, placing the
cut end in water until the flow of sap stops. After
removing from the water, allow the cuttings to dry for
3-4 days. Then dip in a rooting hormone with
fungicide, & place in a well-drained rooting mix. A
1:1:1 mix of sharp sand:perlite:Canadian peat works
well. Keep the mix slightly moist, but never wet.
They will be well rooted in 20-30 days.
V-Grafts. E. milii can be propagated by V-grafting.
This method is often used to avoid cutting rots
associated with rooting cuttings. The extra skill
required means that grafting is more likely to be used
for select cvs by growers & serious hobbyists.
A stock plant is cut at 2-3" above the soil line. A 3/4”
deep V-shaped cut is then made into the stock. A 2-3"
stem tip (scion) is removed from the plant to be
propagated, & the cut end is trimmed to form a 3/4"
wedge, matching the V cut in the stock. Immediately
after the cut surfaces stop bleeding, insert the scion
into the stock, and wrap them together securely with
grafting tape.
Seeds. Seeds can be used to propagate E. milii, but
are mainly used for developing new cvs. In Florida
plants rarely produce fruit (a three lobed schizocarp)
without help from man. Pollen release & receptivity
of the stigma usually do not coincide for a single
plant, which in nature encourages out-crossing. So
you need 2 or more plants, preferably of different cvs.
Controlled pollination increases seed set, & is used by
breeders to develop new cvs. Seedlings will bloom in
5-8 months.
PRODUCTION & SITE SELECTION.
The most important requirement for both production
and landscape use of E. milii is a substrate with
excellent drainage, or a site that does not flood. The
other requirement is at least 70% sun. With some
shade during midday, “flower” color is better in some
dwarf forms. Too much shade causes greening. An
open site with good air circulation also is necessary.
Nursery production is easiest where the water
reaching the plants can be controlled. A cover to shed
rain is considered a requirement. Irrigation should be
done by hand or a closely monitored semi-automatic
system. Unless you are very familiar with the
watering system, automatic (timed) irrigation is a
recipe for failure.
In a landscape, a rockery set aside for succulent plants
is an excellent location for crown-of-thorns, where it
can be planted with other plants with similar
requirements. Remember that low water & full sun
are required. If drainage is a problem & there is no
existing rockery, consider building up a 12 -18"
raised bed using crushed rock & sandy soil.
Choose an area of the landscape that does not receive
water from sprinklers. This is a particularly important
consideration if you are installing a bed in a landscape
with an existing sprinkler system.
Choose a sandy, gritty soil with some added organic
material (peatmoss, coir or thoroughly rotted
compost). In beds, space plants about 2' apart to
allow for air circulation. After planting, water
around the base of the plant without wetting the
foliage, and maintain the soil so that it is just moist.
MAINTENANCE.
Once established, crown-of-thorns requires only an
occasional watering, allowing the top 1" of soil to
dry out between applications. It is important not to
over water, particularly when day temperatures are
below 75EF. The plants survive drought, but under
extreme drought leaves will drop. Some time during
both the middle of May and October apply a light
application of a complete, slow release fertilizer.
Since crown-of-thorns is not fast growing, pruning is
usually not necessary until the second or third year of
growth. Pruning is best done during cool, dry
weather to lessen the risk of stem disease. With the
species lightly prune, removing only dead & overly
tangled stems. Perform a major pruning every 2-3
years in late Spring. For the compact varieties, thin
out at the base to permit adequate air circulation.
PESTS AND DISEASES.
There are few serious pests: scale insects &
mealybugs, & occasionally spider mites & thrips.
Diseases are of more concern. The most serious can
be prevented by avoiding situations where the soil or
foliage remains wet. Remove yellowing leaves &
dead foliage that becomes impaled on the spines.
These promote disease development by trapping
moisture. Diseases include bacterial & fungal leaf
spots, fusarium & rhizoctonia stem & root rots &
botrytis flower blight. Cold damage (soft stems &
burned leaves) should be removed as soon as the
damage is evident. Protect plants if temperatures
drop below 30EF. Call a local CES office for
management recommendations.
CULTIVARS FOR SOUTH FLORIDA.
There are many cvs of E. milii, mostly of hybrid
origin, produced either naturally or through
controlled crosses, & designated E. x lomi. These may
be divided into 2 broad groups: the more common, older
types; & the recently developed Thai hybrids.
The Older Types. The California hybrids were
developed by Humel starting in 1960, and are often
referred to as the “giant crown-of-thorns” series (e.g.
‘Rosalie’, ‘Vulcanus’, and ‘Saturnus’) and were
developed for their stout stems and larger
cyathophylls. The formal name E. x lomi California
Group has been proposed for this group of plants.
Natural crosses similar in appearance, but with
thicker leaves and thinner stems, were collected in the
wild in Madagascar, then propagated commercially in
Germany. This group includes varieties like
‘Somona’ & ‘Gabriella’, & the formal name E. x lomi
Heidelberg Group has been proposed for this group of
hybrids. Many of these & other E. milii varieties are
available from specialist growers.
Locally available in South Florida, and of interest as
a bedding plant, is the recent introduction by Oglesby
of ‘Short and Sweet’ TM, a compact dwarf with soft
spines, dark green leaves, and masses of small bright
red cyathophylls for much of the year. These are
excellent for use as groundcover in a sunny location,
as is ‘Mini-Bell’ a dwarf cv with a tight growth habit
covered with many small red inflorescences & dark
green leaves.
The Thai Hybrids. Over the past 20-30 yrs growers
in Thailand have developed hybrids with much larger
flowers (i.e., cyathophylls) than previous cvs, with a
seemingly infinite variety of color combinations.
These range from all shades of red & pink to cream &
yellow, often with blends of different colors. The
subtle pastel shades of some cultivars remind you of
old fashioned roses, & the masses of closely-packed
cyathophylls remind you of hydrangeas. The color of
some cvs changes as they develop. Sun &
temperature also affect color. Full sun to 30% shade
is considered optimal.
Another attractive feature of these plants is their
compact, upright form, as compared to the more
leggy, twisted growth of E. milii cvs, which can
become a tangle of unattractive stems if not carefully
trained. In addition to having stout stems & a more
attractive form, many of the Thai hybrids have more
handsome foliage that is larger & a brighter green.
In Thailand these plants are known as “poysean”
(Chinese for 8 saints) & are regarded as bringing good
luck. Their exact lineage is uncertain, & the formal
botanical name E. x lomi Poysean Group has been
proposed for them.
More than 2000 different cvs have been developed in
Thailand, most of these having local Thai names.
Increasingly they are becoming available in the US,
either with names in English or simply designated by
color. The first introductions to the US were from a
Florida nursery, & were called E. milii Super
GrandiflorumTM. This name has no botanical
standing, though it may be used in the trade.
Some of the more widely available cvs are described
below using names found in current catalogs &
advertising. There is confusion over names, & some
cvs appear identical. Anyone considering producing
these plants or using them in landscapes should not
rely solely on the descriptions below. You may wish
to visit web sites of those growers who post pictures.
Color descriptions refer to cyathophylls.
‘Jingle Bells’: soft pink with hints of red & green.
‘Spring Song’: light creamy yellow. There is also a
dwarf form, ‘Mini Spring Song’.
‘Summer Song’: rich, creamy yellow with emerald
green splotch at the center margin.
‘Fall Song’: cupped, light creamy yellow.
‘New Year’: color changes from buttery yellow
to cherry red.
‘Pink Christmas’: cream, becoming suffused with
pale pink & reddish streaks.
‘Valentine’: striking, bright scarlet.
‘Rosy Yellow’: rose pink blend with raspberry red
splotches; prominent yellow cyathia.
Interesting leaf venation.
Source : http://www.tropicanursery.com/euphorbia/pdfs/crown-of-thorns-production.pdf
