If many bulbs and their ilk are valued principally for their color, then cacti and succulents are the plants to turn to for form. Yes, many dazzle us with their silky, almost psychedelic flowers, and they do offer the entire range of textures and many colors, but those sculptural, bizarre, sometimes animal-like shapes are what offer seemingly limitless opportunities for creative compositions. If one of them in a pot brings to mind an object d'art, then a collection of them recalls an entire gallery.
A popularly held notion asserts that all cacti and succulents are easy to grow. This is the same as saying all annuals are grown for their flowers or that dahlias cannot be grown in containers. While many cacti and succulents survive for years with minimal care, some of them thrive with more attentive care, and a few of them are among the most challenging plants to keep alive in cultivation.
As they do benefit from some specialized care, here are a few points to keep in mind:
Use a porous potting mix.
Most cacti and succulents require a very well-drained mix, high in porous ingredients and relatively low in organic matter. Many cactophiles use a mix (often called Barad mix after its formulator, Dr. Gerald Barad) that combines 50 percent mineral particles with 50 percent organic matter:
3 parts commercial potting mix high in bark and/or coir (composted coconut fiber) 2 parts pumice (a mineral product similar to, but structurally stronger than, perlite or vermiculite) 1 part Turface (this product is similar to cat litter but it doesn't break down)
Such a mix allows water to drain through quickly yet retains enough moisture around the roots to prevent desiccation. Although the high porosity translates to the need for surprisingly frequent watering during active growth, it also means that virtually no water exists in the mix when plants are dormant. This is a good thing. Read on.
Observe the dormant period.
Like many other plants, most cacti and succulents require some down time to ensure continued healthy growth, but their rest does not always occur during winter. While the great majority of cacti are winter dormant, many other succulents want to grow actively in winter, whether in a greenhouse or on a windowsill or outdoors (if hardy). Too much water during dormancy will kill many cacti and succulents. When it doubt, don't water them. Generally, if a plant loses its luster or begins to shrink during its normal period of active growth, it is definitely time to give it water. However, if you notice shriveling occurring as dormancy approaches, resist the urge to keep watering as much as usual, because the onset of dormancy is a signal to begin to reduce (but not suddenly stop) watering. An infrequent dribble of water - barely enough to slightly moisten the surface of the mix - should keep most dormant cacti and succulents happy. Dormancy often results in a leafless plant, so don't be surprised if a plant you bought in spring drops all of its leaves in fall. Learn a plant's dormancy needs before adopting it.
 A young specimen of Pachypodium namaquanum makes an impact in a carefully chosen container. It will soon need to be moved, however, into a larger pot to keep growing without check.
Full sun is not always required.
Holiday cacti and some others break the cactus mold by requiring shade at certain times of the year and in regions with naturally strong sunshine. Similarly, many haworthias and a good number of euphorbias must be protected from strong sun to avoid scarred and stunted growth. Again, do a little research before attempting to grow these plants.
Keep them hot year-round?
All of these plants grow in deserts, and deserts are always hot, right? Wrong. Many do grow in arid regions of the world, but these areas are not always hot. Deserts can get cold, and many cacti and succulents can withstand surprisingly low temperatures, often to freezing and sometimes far below. On the other hand, temperatures below 55F (13C) will kill many of them. Get out the books, go online, and ask questions.
Know their individual growth rates.
While many succulents grow at amazingly slow rates - and sometimes do not appear to grow at all over a given season - others approach weediness in their exuberance. Many sedums and hens and chicks (Sempervivum) multiply like bunnies, and a climbing onion (Bowiea) can easily produce a five-foot thready stem in one season before going totally dormant. Use that vigor to produce an impressive display in a relatively short time.
Handle with care.
Finally, don't be put off by the prickly nature of many of these plants - just be careful when near them or when handling them. Also realize that many succulents are quite fleshy and even brittle and can be damaged by rough handling. Treat your cacti and succulents as you would any other plant - by providing for their needs - and you will find them just as rewarding (maybe more so) as a petunia, ivy, or geranium. Look back to Part 1 on the elements of design to see a great many cacti and succulents used beautifully and creatively.
A SELECTION OF CACTI AND SUCCULENTS FOR CONTAINERS
Aeonium arboreum 'Zwartkop'The solitary rosettes of young, unbranched plants provide interesting circular outlines, while older, multistemmed specimens bring to mind colonies of prehistoric underwater creatures. The rosettes of plants grown in full sun look like shiny black old-fashioned roses to me.
AgaveLike aeoniums, agaves offer another useful group of flowerlike rosette forms, and some might even suggest the tentacles of squids, especially larger, older examples of A. americana and its selections. Variegated forms make stunning specimen plants, while a group of several smaller ones in a roomy pot makes an assertive statement of color and form.
AloeMost aloes have thick leaves in dense clusters or rosettes and rather coarse textures, especially A. ferox. Others, such as A. vera (used for treating burns) are more open and reveal a great deal of space between their quite linear leaves.
Beaucarnea recurvataRemember the exploited truffula trees of Dr. Seuss's tale about the Lorax? Pony-tail palms remind me of them, with bushy heads of strappy foliage above bare, sometimes gently curved trunks arising from swollen bases. Use solitary specimens as a focal point or as part of a grouping of containers.
Bowiea volubilisBasically looking like a mass of green threads coming out of a paper-covered bulb, climbing onion lends fine texture and bright green accents to a composition. Train the stems on a form or over another plant, or let them dangle from a pot or hanging basket.
Ceropegia linearis subsp. woodiiSeveral rosary vine plants put together create a fine-textured veil of silver-marked foliage dangling from a hanging basket or tall pot, while a single stringy stem offers a bit of contrast to other plants it may clamber over. The little "potatoes" sometimes produced where the leaves join the stem can be used to start new plants.
CrassulaWith time, C. arborescens and C. ovata, the silver jade and regular jade plants, become thick-stemmed, coarse-textured miniature "trees" that look much older than their age. C. perfoliata var. minor, perfectly described by its common name, propeller plant, appears to be constantly spinning. All three species mix attractively with linear and rosette shapes.
EcheveriaResembling in basic form their more cold-tolerant relatives (sempervivums, commonly known as hens and chicks), echeverias offer a wider variety of colors - including icy green, ghostly gray-blue, and moody dark purple - in visually engaging rosettes, many sporting wavy edges. Flowers in hot shades appear on arching stems above the plants, and the rosettes do not die after flowering, unlike hens and chicks.
Epiphyllum crenatumUse this plant as a "what is that?" note in a planting. Zigzag stems (no, they are not leaves) grow in unpredictable directions and offer a unique combination of line and form, unforgettably spilling out of a large pot or hanging basket. Feel fortunate when the water-lily-like blooms appear.
EuphorbiaMany euphorbias are best left by themselves as showy individual specimens, but E. lactea and E. tirucallii mix nicely with other succulents in mixed pots. Milkbush (E. tirucallii) resembles spiky, lumpy green animal horns, while the stems of E. lactea look like handfuls of thin green pencils (lit with red in the selection 'Sticks on Fire').
Graptopetalum paraguayenseThe common names ghost plant and mother-of-pearl plant derive evocatively from the very useful, almost pastel coloration (in shades of blue, gray, and pink) of the rosettes of thick leaves. Sensational when combined with anything pink, dark blue or purple, or gray, including pots and topdressings.
HoyaWax plants provide plenty of linear interest to a container, especially when dangling from a hanging basket or trained onto a hoop. Clusters of waxy, starry flowers add some color and punctuate the overall linear appearance. Have patience with these; many grow slowly.
KalanchoeHere is a feast of colors, forms, and textures: K. beharensis (felt bush) produces roughly triangular, brown-tinged, finely haired leaves on big, coarse plants. K. pumila makes a gently cascading, fine-looking mass of small, almost chalky leaves and lilac flowers in late winter. And K. thyrsiflora looks like a nested stack of red-edged, greenish-gray, thickcut potato chips.
OpuntiaWhile most members of this genus seem to inject their tiny, persistently itchy spines into your skin just by looking at them, don't give up on the entire group: some of the less pernicious or even spineless species (such as O. ficus-indica var. inermis) make eyecatching, coarse-textured accent plants or focal points.
PachyphytumThese are basically elongated versions of their Graptopetalum relatives (listed above) but are usually more rounded and softer looking. Most, including the chubby, poetically named moonstones (P. oviferum), appear to be covered with frost or dusted with confectioner's sugar.
PachypodiumWith age, most pachypodiums become statuesque, treelike specimen plants covered in spines, and they bear explosive-looking leaf rosettes. Grow them by themselves in their own pots or group them with mounded, less coarse-looking plants for a study in contrast of form and texture.
Portulacaria afraSimply put, the elephant bush looks like a more refined and relaxed jade tree (Crassula ovata, listed above). Use it in contrast with coarser and more linear succulents. The variegated selection adds color interest but may look a little lost among coarser plants.
RhipsalisMost rhipsalis look like green waterfalls or mop heads: a mass of green lines rushing from a hanging basket or tall pot. A large hanging basket looks like a giant wig, while a smaller plant emerging from a container suggests a billy goat's beard or goatee. Few other plants - with the exception of grasses - are so full of lines, but these hang down.
SedumTough plants that offer color, line, form, space, and texture. I think sedums provide more for a designer to work with than any other succulent genus. Some cover the "ground" in a pot (S. acre and S. xrubrotinctum); others produce long ropes that hang or cascade (S. morganianum and S. rupestre 'Angelina'); and others make fleshy, sturdy mounds of different heights (S. cauticola, S. 'Herbstfreude', S. sieboldii, and S. spathulifolium 'Cape Blanco'). Colors range from green to red to gray to yellow to purple to pink, and that applies to the flowers almost as much as it does to the foliage. Don't garden in the sun without them!
SempervivumRosette-forming hens and chicks, which are much more cold hardy than their bigger yet more elegant cousins the echeverias, can grow as thick as thieves and create the impression of pointy green lava spilling out of strawberry pots or low bowls. Use the larger ones as starburst accents in a mixed pot, and let the smaller, more prolific selections quickly fill large areas of "ground."
 Like many succulents, the dark but reflective rosettes of Aeonium arboreum 'Zwartkop' resemble undersea creatures. Their depth of color is related to the amount of sun they receive.
 Sempervivum and the related Jovivarba and Rosularia grow best in a welldrained medium with plenty of sun, although they tolerate shade if not kept too wet.
 A strawberry jar pocket provides an excellent home for Sempervivum arachniodeum (the cobweb houseleek), which quickly fills out. (While appreciating the drainage offered by a jar, these older plants need heavier water.)
 The solid structure of Agave ferox perfectly complements soft, airier grasses such as this Muhlenbergia dumosa.
 Many sedums, such as Sedum telephium ssp. ruprechtii, are hardy in much of North America; the cold they receive during winter dormancy promotes strong growth the next season.
 Not all succulents are small and solid-looking. Members of the genus Cussonia can become quite large and offer light feathery foliage.