adenium roem

8/7/2019 Adenium Roem

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Adenium Roem. & Schult.

Family Apocynaceae

published in [reference + year] [if republished, enter second reference]

This genus name is correct

Common names: Karoo rose, desert rose, impala lily, Sabi star, or simply adenium

Sheet based on Adenium Culture: Producing Large Specimens Quickly by Mark A.Dimmitt - used with permission

Associated groups: Caudiciforms

Introduction to the genus

Plants of the genus Adenium make superb collector's specimens whether maintained as

dwarfs or grown into small trees. Both the swollen, twisted stems and large bright

flowers are eye-catching. But despite their great beauty they are not very popular and

are seldom grown to large sizes, even by succulent collectors. Adeniums have acquired

an undeserved reputation for being slow-growing and temperamental. They are in fact

fast-growing and easy to cultivate when given proper care. This article is devoted to

detailing their cultural needs.

Whether regarded as full species or un-deserving of even varietal status (compare

Plaizier, 1980, with Rowley, 1983), the taxa are distinctly different horticultural entities.

Their differences must be recognized in order to grow them well. The culturaltechniques and resulting performance described here are for seed-grown plants in

containers in the semi-desert climate of Tucson Arizona, outdoors from April through

October. Expect similar performance wherever comparable sun and warmth can be

provided. Old, especially wild-collected, specimens should be treated much more

carefully.

Adenium obesum in Yemen

Breeders in India and Florida are growing thousands of adeniums in fields, and manyout-standing variants have appeared. There is a seedling from Florida with velvety,
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blackish-red flowers. Several forms with very ruffled petals have been selected in India.

Many hybrids have also been produced in recent years.

General cultivation techniques

A fundamental change in the prevailing perception about adeniums is necessary to grow

them well. The common wisdom is that they cannot tolerate a good watering. I've seen

many ten-year old plants only a few inches tall stunted by chronic water stress. The

essence of this article can be summarized in two crucial rules:

Grow adeniums as wetland tropicals, not desert plants.

Reject the first rule when the plants are dormant.

Watering

While some populations do grow in extremely arid deserts, it does not necessarilyfollow that they need to be wedged in a rock crevice and constantly deprived of water.

Many xerophytes evolved from tropical species that adapted to aridity rather than

migrated as the forest retreated due to climatic change. Adeniums are apparently among

these, and most of the taxa have not lost their affinity for more mesic growing

conditions.

Fig.1 The original seedling of

Adenium 'Endless Sunset' at five years old.

The plant stands five feet above the 18 inch pot

All taxa (except possibly Adenium obesum (A.socotranum)) respond to generouswatering during warm weather. Treat them as if they were tropicals such as hibiscus or
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gingers and they will respond dramatically. This is especially true of many of the

hybrids which exhibit great vigor. Keep the potting mix continuously moist during the

active growth season. Root-bound plants may be watered almost daily in hot weather.

Adeniums are planted as hedges in the Philippines and India, where they thrive on more

than 60 inches (1500mm) of rainfall a year1). The taxa that lack an obligatory dormancy

(Adenium obesum andAdenium swazicum) can also be watered through the winter ifthey are kept warm (at least 80F, 27C days, 5OF, 10C nights), but let the medium

become nearly dry between irrigations.

This is sufficiently important to justify repetition; Water them as if they were coleus or

tomato plants while they're growing in hot weather, but as if they were delicate, rot-

prone cacti during winter. Adeniums are extremely susceptible to rot when watered too

frequently during cool weather or if chronically waterlogged at any season. Use of a

well-drained potting medium prevents most rotting problems.

Light

Adeniums require high light intensity, 5000 to 8000 foot-candles outdoors (full sun is

about 10,000 fc in clear, dry air). They tend to grow spindly in climates with cloudy

summers or if they receive sun less than half the day. In desert climates most taxa

perform best in light afternoon shade (30-50%). Mature plants of all taxa can be

acclimated to full desert sun, though only Adenium swazicum performs well in extreme

heat. In cooler, cloudier, or more humid climates adeniums should be in full sun all day

outside or with 4000-6000 footcandles under glass.

Keep the plant facing the same direction all summer. If the pot is rotated, intense sun

can severely burn the formerly shady sides of the stems. Autumn is the most hazardoustime, when the sun is low in the sky but still strong. The bases of young plants are

especially sun-tender and should be protected from the sun of arid climates until they

are at least three inches (7-8 cm) thick. When first put outside after winter storage,

foliage may scorch. This is not serious; new, sun-adapted leaves will soon appear

Temperature

Adeniums thrive during moderately hot weather (85-95F, 30-35C), preferably

accompanied by moderate to high humidity. However, growth and flowering seem to be

suppressed by temperatures consistently above 100F (38C). Plants grown outdoors in

southern Florida2)

, or in a greenhouse in southern Arizona, grow nearly year-round. Thecommon factors in these two locations are moderately high temperatures and high

humidity. Plants grown outdoors in southern Arizona begin vigorous stem-growth only

after the monsoon (humid tropical air) arrives in July.

Dormancy is induced in all taxa when nights regularly fall below about 50F (10C).

When completely dry and dormant they can tolerate near-freezing temperatures, though

there is increased risk of root-rot below 50. Even a light frost will cause severe damage

and usually subsequent death from rot to all adeniums exceptAdenium swazicum,

which tolerates upper 20sF (about -2C) when dry and dormant.

Feeding
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Fig.2 Four-year-old cutting of A. 'Crimson Star'. It spreads

four feet in an 18-inch pot and shows substantial stem thickening

Adeniums also respond well to regular and generous fertilizing. I use slow-release

fertilizer in my potting media and inject my irrigation water during the growing season

with a balanced fertilizer such as 20-20-20 plus micro-nutrients at a concentration of

200 ppm nitrogen.

Inadequate watering and feeding are the primary reasons adeniums have been regarded

as slow-growing. Generous culture produces literally unbelievable results. (An eight-

month-old plant splitting a six-inch pot that I entered in the seedling category at a CSSA

show was disqualified by the judges because they didn't believe it was less than the limit

of a year old.) Specimens several feet tall and wide in 18-inch containers can be grown

in only three to five years (Figs.1, 2) and sometimes even less.

Adeniums seem to require high nitrogen for both strong growth and copious flowering.

For one year I used a low nitrogen fertilizer (2-10-10) on most of my mature adeniums

in an attempt to thicken their stems while minimizing further elongation. Not only did

the low-nitrogen plants not thicken appreciably, they also flowered poorly that year.

(Well-fed plants flowered normally.)

Overwintering

Adeniums must be grown in containers in climates with frost or cool, wet winters.

Adenium obesum, Adenium swazicum, and some of their hybrids, can be kept active by

maintaining night temperatures above 50F (10C). The other taxa will enter various

degrees of dormancy in autumn regardless of conditions.

Recognizing dormancy is critical to a plant's survival. Not only does the timing and

depth of dormancy vary among taxa, but individual plants (even of the same clone) vary

with cultural conditions from year to year. Dormancy is often signaled by a sudden

yellowing and dropping of most or all of the leaves. Some weeks before this occurs you

may notice a significant decline in water consumption. Either of these events demands

sharply reduced watering.
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There may be some shedding of older leaves near the autumnal equinox, apparently in

response to shortening days. This event does not require less watering if the stems

continue to grow new leaves. Partial defoliation may also occur at other times in

response to a missed watering or a dramatic change in weather. As long as stem-tips are

actively producing new leaves, keep watering normally.

Dormancy varies from complete defoliation (Adenium boehmianum and Adenium

multiflorum) to just curtailment of stem growth (A.somalense and A.arabicum retain

leaves if watered sparingly). Some taxa flower primarily during dormancy either with or

without leaves (Adenium obesum (forms previously known as A.somalense and

A.multiflorum)).

Fig.3 The same individual of 'Endless

Sunset'

as in Fig.1 at 13 years of age. It standsseven feet above the 30-inch pot, having

added two feet in height in the preceding

eight years plus a lot of stem thickening.

Fig.4Adenium obesum (Big Mama)

filling

a 45-gallon container at about 12 years of

age

It measures 71/2 feet (2.3 m) tall from theground and the exposed root-mass3)is

34 inches (86 cm) wide. Grown by John

Lucas

(photo) of Tradewinds South Nursery,

Florida.

If a warm sunny space is not available or if the plant is an obligate winter rester, reduce

or stop watering when the nights regularly fall below 50F (10C) or when a plant signals

onset of dormancy. Place in a dry, cool but frost-free location. Light is not essential to

dormant plants, except that the winter bloomers will not flower normally in poor light. I

have successfully overwintered mature plants ofAdenium obesum, Adenium swazicum,andAdenium multiflorum under a carport, with no water, from November to April. I
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winter most of my large plants in an unheated and uncooled greenhouse in which

temperatures approach 90F (32C) on sunny days and commonly dip below 40F (5C) at

night. Under these conditions many plants continue flowering well into the winter, but

they eventually shut down. This is colder than ideal and a few plants succumb to rot

each winter.

Recognizing the end of dormancy is even more crucial. Root rot most often strikes in

spring as a result of too much water too early; overpotted plants are most susceptible.

The arborescent form ofAdenium obesum (A.somalense) from northwestern Kenya is

particularly sensitive. On the other hand, adeniums will usually not leaf out if the

potting medium is completely dry. Therefore I recommend watering sparingly through

the winter (as little as once per month for large, leafless plants). Watch for expanding

terminal buds in spring. At the first sign of activity increase the watering frequency

gradually until the plants are in full growth.

Potting

Adeniums need ample root-space for rapid growth. Root-bound plants greatly curtail

their growth even if watered and fed generously Plants should be repotted frequently

until they attain their desired size. Plastic, porous clay, concrete, and stoneware pots are

all suitable. But be aware that the massive roots of adeniums have no respect for

expensive ceramic pots. Use thick-walled and preferably bowl-shaped containers to

avoid breakage.

Potting mixes are more variable among growers and are the subject of more debate than

any other horticultural topic. I will stress only two critical points here. First: The potting

mix MUST provide excellent drainage and aeration if the plants are to survive thewatering regime I recommend. Any medium that satisfies these criteria is at least

satisfactory. Adeniums perform well in media ranging from 4:1 pumice : humus to pure

Sunshine Mix #1 (which is mostly peat moss) and at pH values ranging from 5.5 to 8.

Second: Each grower must experiment to find the potting medium that works well for

him or her. Sorry, there is no better answer!

It is impossible to overemphasize the importance of experimentation. For example,

several Tucson growers have concluded that the humus ingredient significantly

influences performance. Adeniums and many other succulents perform superbly in

media containing Sunshine Mix, Ball Mix, and coir (a peat-like product made of

coconut husk) and poorly with several other brands. We don't know whether theseresults are due to the products or culture conditions; both vary greatly. It's a good

practice to obtain several plants of the same kind and pot them in different mixes to

determine the best one for your cultural conditions.

Repot during the active growing season, the earlier the better. Plants that have not filled

the pot with roots by fall are much more likely to rot from an ill-timed watering. Do not

water for a week or so after repotting if any large roots were damaged or if the weather

is not warm and dry. If large roots have not been damaged, follow the tropical,

nonsucculent model and water repotted plants immediately. Water stress can trigger

dormancy which may not break until the following summer. Treating cuts with dusting

sulfur and watering-in with fungicide are probably beneficial, though I rarely do so.
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The plant can be raised above the previous soil line, exposing more of the caudex or

succulent roots. Beware that newly exposed roots are susceptible to sunburn; they

require a full growing season of gradually reduced shading to acclimate to full desert

sun.

Pests and diseases

Fig.5 A display of large adeniums

at the 1995 CSSA Convention in Tucson, Arizona

Pests rarely damage adeniums grown outdoors. Sometimes new leaves are deformed by

an unseen pest in the growing tips (probably thrips or psyllids). Control requires a

systemic insecticide; several applications may be necessary. Despite the extremely

poisonous sap. rodents occasionally gnaw on roots and trunks.

Indoors mealy bugs, spider mites, aphids, and white flies often infest plants; all can

cause severe damage. Use pesticides carefully, as adeniums are sensitive to some.

Insecticidal soap and micro-encapsulated diazinon (Knox.Out) are safe for the plants (I

make no claims for humans or pets). The systemic Dimethoate 267EC is not phytotoxic

if used as labelled at temperatures below 90F (32C). Beware; Cygon has the same active

ingredient but the inert solvent kills foliage.

Roots are susceptible to water molds (e.g., Pythium and Phytophthora) which thrive in

waterlogged soils. Prevention is the best strategy because most fungicides are

ineffective against this group and the few that are (e.g., Ridomil, Subdue, Banrot) are

expensive. Use of a well-drained medium and careful watering prevents most root rot.

Warning; do not use any pre-emergent herbicide with the active ingredient oryzalin

(e.g., Surflan) on adeniums or most otherApocynaceae(e.g., Plumeria, Pachypodium,

Mandevilla, Macrosiphonia). A single application permanently arrests root growth and

the plants slowly die. Oleanderis the only member of the family tested that is

unaffected 4).

Etiolation (weak, elongated growth) is caused by too much water and/or fertilizer

combined with too little light or poor air movement. This common problem is easilyremedied by improving the growing conditions and pruning off leggy stems.
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Care of mature specimens

When a plant reaches the desired size, reduce watering and feeding to slow further

growth. Even in hot weather, adeniums maintain well on as little as two waterings per

month. Hard-grown plants have leaves only at the stem tips, fully revealing their

gnarled forms. While floriferousness may decline noticeably, hardened plants are moreresistant to pests and diseases.

Propagation

Superior clones can be propagated by cuttings. Large hardened stems will root

dependably but may take several months. I get the fastest results with either vigorous

four- to six-inch (10 to 15cm) tip-cuttings or the next lower stem segment of semi-

hardened wood dipped in liquid rooting hormone, and stuck in a coarse medium (e.g.,

perlite-vermiculite) under mist with bottom heat of 90-95F (32-35C). Under these

conditions roots form in two to four weeks. Using a fungicide formulated against water

molds reduces loss. Keep them well watered; cuttings that wilt usually fail to root.

Fig. 6 A large specimen ofAdenium obesum

(previously a diminutive taxon, A.somalense var. crispum)

at seven years from seed.

It is two feet (0.6 m) tall in a 12-inch (30 cm) pot.

Grafting is also an effective method of propagation, and it can also improve growth

form. Spindly plants such as typical clones ofAdenium swazicumbecome noticeably

sturdier when grafted onto a stouter rootstock. Grafting is also useful for combining a

superior flower with a caudiciform rootstock or for placing several flower types onto a

single plant. Cleft-grafting of half-inch (1.25 cm) thick stems produces a smoother
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union than side-grafting. I've had greater than 90% success using actively growing

rootstock; the scion may be dormant or active.

Growing from seed is easy though pollination is a challenge (Anderson, 1983) and seed

cleaning is tedious. My success when using known compatible parents ranges from

nearly 100% in some years to zero in others. Many clones seem to be either male- orfemale-sterile, and some rarely cross in either direction. After the follicles mature,

remove the coma (tuft of hairs) at both ends of each seed before sowing.

Seeds germinate in about a week at 85F (30C). Treating with fungicide before sowing

reduces loss. Seedlings of most taxa grow rapidly. They will usually keep growing

through the first winter under tropical conditions and sometimes a second before

obligate dormancy appears. Seedlings of several taxa and most hybrids will flower

within a year or two, sometimes in as little as six to eight months. Adenium obesum

(Adenium somalense crispum) and Adenium multiflorummature in about three and five

years, respectively.

Producing large specimens

As is true of many plants, only young adeniums have a capacity for rapid growth.

Production of large specimens requires pushing seedlings or small cuttings with

generous culture during their first two or three years. Growth slows greatly in maturity;

old plants can seldom be induced to resume vigorous growth. The 'Endless Sunset' in

Fig.3 is eight years older than the photo of the same plant in Fig.1, so it attained most of

its present size in its first few years.

Fear not that plants pushed in this manner will lose their character. Large plants withluxuriant foliage make lots of photosynthate, which in mature adeniums is channelled

largely into stem thickening. Don't compare adeniums with related Pachypodium

species, which do indeed grow spindly weak stems when pushed, especially at high

temperatures. I have grown the arborescent form ofAdenium obesum (A.somalense) to

eight feet tall in two years from seed. In their third year they entered maturity in which

flowering began, stem elongation slowed, and the main stems began thickening 5). In

their fifth year they are well on their way toward the mini-baobab form of wild plants.

Growth form (i.e., tree or shrub) is genetically determined, while growing conditions

during youth strongly influence ultimate size.
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