This must be one of the sillier horticultural names. Tree houseleek, Aeonium arboreum, is neither a tree nor related to leeks. The biggest cultivars can not stand much more than three feet tall. Above that, their succulent foliage gets too heavy for their fleshy stems and fine roots. They perform well as houseplants only within very sunny situations.
Formerly common tree houseleek, with simple green foliage, is not so common anymore. Almost all popular modern cultivars are variegated or bronzed, with wide foliar rosettes. Variegation ranges from bright lemony yellow to creamy white. Bronze ranges from light brown to very darkly purplish. Foliar rosettes are about four to eight inches wide.
Plumply conical trusses of tiny yellow or chartreuse flowers bloom for spring. They are neither numerous nor brightly colorful, but are weirdly interesting. Fresh spring foliage is most colorful and lush. It can fade and partially shed during arid summer weather. New plants propagate very easily from dragging stems or cuttings of pruning scraps.
Large pots, urns and planter boxes filled with ridiculously colorful blooming annuals are certainly nothing new. However, more small perennials and even a few small shrubs and trees are being planted along with the annuals, and allowed to stay indefinitely as fewer annuals get replaced around them as the seasons change.
These plants only need to be tolerant of confinement, regular watering and the comings and goings of the annuals around them. Upright plants should go in back, behind the lower annuals. Cascading and ground cover type plants should go in front.
Small forms of New Zealand flax and trunkless dracaena palms (Cordyline spp.) add texture, form and motion to large planters, but may eventually get too big if not properly pruned. Larger shoots can be pruned out to allow smaller shoots to take over. Alternatively, overgrown plants can be removed and put out in the landscape when they get too big.
Hollywood and Rocky Mountain junipers have striking form if pruned to show it off, and are easier to contain with selective pruning than reputed. Even without the interesting branch structure of junipers, arborvitaes are appreciated for their similar finely textured foliage and their rich green or yellow color. ‘Blue Rug’ juniper, a grayish ground cover juniper, cascades nicely from large planters.
Large succulents that tolerate water, such as good old fashioned jade plant and various aeoniums, offer bold texture and form in the background. They are easy to prune as they grow, and do not have aggressive roots. Low clumping aloes do the same in front.
Euonymus fortunei, English ivy, various iceplants and other ground cover plants do well cascading over the edges of large planters.
There really is not much limit to the variety of perennials and small shrubs and even trees that play well with others in planters of blooming annuals, and do not mind the confinement and regular watering. Annuals are still the best for flashy floral colors. Yet, the other plants excel in form, texture, foliar color and motion in the breeze.
The long, white hair of old man cactus, Cephalocereus senilis, that protects it from sun scald in harsh climates is what make it so striking in home gardens. However, the sharp spines concealed by the hair make it more appealing from a safe distance, like in the background behind lower perennials. The white, yellow or red flowers are rarely seen, since they only bloom on old stems that are at least a dozen years old. Such old stems are often cut down to the ground before they bloom because they get too tall and awkward, or because they eventually lose some of their hair as they get too old. There should be plenty of hairier, younger stems emerging from the basal clump to replace the older stems anyway. Individual stems rarely develop branches. Although old man cactus can get quite tall, it is typically kept less than fifteen feet tall.
Wandering Jew, spider plant, various philodendron and jade plant were among the most popular houseplants of the 1970s. They are as easy to propagate as they are to grow, so were popular gifts for friends and neighbors. Jade plant, Crassula ovata, commonly grew too big to stay inside without pruning. It fortunately grows better than the others outdoors.
Jade plant does not grow fast, but can eventually get more than six feet tall, with densely rounded form. The succulent stems of such large specimens get quite plump, but remain rather fragile. The paired evergreen leaves are thickly succulent, and mostly a bit longer than two inches. Clusters of tiny pale pink or white flowers are not especially impressive.
At least one cultivar is variegated with irregular white stripes. Another is somewhat ruddy with relatively compact growth. Others exhibit tubular or curly leaves. Foliage can fade or develop narrow red edges in response to harsh exposure or heat. It is also susceptible to frost damage. Jade plant is mildly toxic, but also potentially appealing to dogs who chew.
There really is no way to neatly classify succulents. Many are spiny cacti with fleshy stems without recognizable foliage. Others are euphorbs (related to poinsettias) that may resemble cacti, or may instead have fragile leaves on fleshy stems. Aloes and agaves have bold rosettes of fleshy leaves that obscure their wide basal stems.
The most familiar succulents are small docile perennials, like the many varieties of jade plants and iceplants. Some are flowering perennials like begonias. A few are even grown as annuals, like busy Lizzie (impatiens).
So what do succulents have in common? Well, that is a good question that is open to interpretation. Most would agree that succulents have some sort of fleshy succulent parts for storing water through dry weather. These succulent parts are most often leaves or stems. Yet, yuccas, dracaenas and ponytail palm that are no more succulent than palms, are considered by many to be succulents like related aloes and agaves.
Many succulents are remarkably easy to propagate vegetatively (without seed). Most aloes, some agaves and many yuccas produce pups, which are basal shoots that can be separated as new plants. Agaves that do not produce pups while young will likely produce many pups after they bloom and begin to deteriorate. (Individual rosettes die after blooming.)
Despite the nasty spines that make them difficult to handle, cactus that produce multiple trunks can likewise be divided. Cactus can alternatively be propagated as large cuttings; but because they are so fleshy, should be left out for their cut ends to dry and ‘cauterize’ somewhat before rooting. Many euphorbs behave much like cacti, but are even more hazardous to handle because of their very caustic sap.
The majority of small succulents, like the many jade plants and iceplants, are notoriously easy to propagate by cuttings.
It is difficult to see how string of pearls, Senecio rowleyanus, is related to much more colorful daisies and asters. The small, fuzzy and sickly white flowers are not much to look at, and only clutter the elegantly pendulous and oddly succulent foliage. The round leaves are light bluish green, so actually resemble peas more than they resemble pearls. The stems are so very thin and limber that they can only stand a few inches high, but can cascade to three feet!
Although evergreen, stems of outdoor plants can be cut back while dormant through winter to promote fresher growth in spring. The pruning scraps are very easy to propagate as cuttings. Roots are undemanding and sensitive to rot, so should be allowed to get nearly dry between watering. Bright ambient light without too much direct sun exposure is best. Incidentally, all parts of Senecio rowleyanus are toxic.
Several species of Agave inhabit the landscapes here. Only a few are identified. Some of those that are unidentified could likely be identified if their identities were important to us. For some, identification would be as simple as researching our records. I know what Agave attenuata is only because there is nothing else like it. #3 is likely a variegated and dwarf cultivar of Agave americana. #6 is the surprise of these Six. It is a familiar species that was formerly identified as another genus. Although its relation to the Family should be obvious in regard to physiology, it is not visually similar to others of the Agave genus. I still know it by its older and perhaps less accurate designation. It works for me.
1. Pups of an unidentified agave that was removed last year are a concern because others just like this continue to develop where the agave was relocated from a few years earlier!
2. The parent agave got removed and dumped next to a greenwaste pile after gophers ate its base, but somehow survived. It fell over only recently. Maybe other gophers found it.
3. Gophers also ate the base of this other unidentified agave, which, like the other agave, seems to have survived somehow. Fortunately, it did not leave undesirable pups behind.
4. Agave attenuata arrived as a big cutting with a long stem, and by odd circumstances. The severed stem generated a big secondary rosette, which is now generating four pups.
5. The pup to the lower right of this unidentified agave indicates that its primary rosette may be about bolt and bloom. Although most agaves are monocarpic, their pups survive.
6. Surprise! Fresh from 1985, tuberose, which was formerly Polianthes tuberosa, is now Agave amica. We just installed three, with two more still canned. I hope for many pups.
Like so many fads often do, the vertical gardening fad has become trendier than it really should be. It certainly has practical applications, and is very appealing in the right situations. However, in the wrong situations, it can be more problematic than it is worth.
Vertical gardens can shade and insulate exposed walls, but really do little more than strategically placed shade trees, large shrubbery or even trellised vines can do in that regard. The disadvantage of vertical gardening is that it can hold moisture against the affected walls, and can promote rot if the planters are not installed properly. Planters over windows or decks drip just like any other planters do, staining or dirtying whatever is below. Only free standing vertical gardens (that are not attached to a wall) or those on concrete walls that are not susceptible to rot will not cause such problems.
Water borne pathogens (diseases that disperse in water) can proliferate more in vertical gardens because they get carried with the natural flow of water from top to bottom. Wherever any such disease gets established on a vertical garden, it will likely get carried to everything below. In the ground, such diseases spread slower since they only travel as far as water flows or gets splashed.
The obvious advantage to vertical gardening is that it makes it possible to grow many more plants in very limited space, which is excellent if there is no open ground for vegetable gardening. It can also be a great way to display plants like orchids and certain bromeliads that are more appealing if they hang from above. Staghorn ferns cling to walls naturally.
Another advantage is that vertical gardening can be so aesthetically appealing and unique. Vertical gardens of small, densely foliated succulents hung like tapestries to adorn exterior walls are so much more interesting than simple vines or shrubbery used to obscure such walls. Northern exposures that are too dark for most plants can be adorned with ferns.
Some but not all of of the many succulent plants known as ‘hen and chicks’ are varieties of Echeveria. Likewise, some but certainly not all Echeveria are known as ‘hen and chicks’. Echeveria are so variable that many do not seem to be related, although all have dense rosettes of succulent leaves. Some have very narrow leaves like miniature yuccas. Others have warty broad leaves. Foliage can be simple green, yellowish, bluish, gray, bronze, bronzy purple or variegated. The edges and tips of leaves of many varieties are blushed with red or purple that is more colorful in winter, or with complete sun exposure. Most Echeveria will tolerate light shade. Propagation is very easy from division of pups, stem cuttings and even leaf cuttings.
Cacti have thick, fleshy stems outfitted with nasty spines instead of leaves. Agaves and related aloes have stout, fibrous stems that are mostly obscured by thick, fleshy leaves. (Only a few somewhat rare aloes develop bare trunks and stems.) What they have in common is that they all are succulent plants, collectively known as succulents.
There are all sorts of other succulents. Humongous saguaro cactus have hefty trunks and limbs. Diminutive impatiens (like busy Lizzie) are grown as annuals for their colorful and very abundant flowers. Many succulents have succulent stems. Many have succulent leaves. Some, like the common jade plant, have both succulent leaves and stems. Trailing ice plants, leafy begonias, and sculptural euphorbs (related to poinsettias) are all succulents.
Many succulents store water in their succulent parts because they live in dry climates. Because moisture is such a commodity where they live, cacti protect their succulent stems with sharp spines. Agave protect their leaves with sharp teeth. Euphorbs are equipped with caustic sap, and many also have spines like cactus have. Fortunately, most succulents are not so unfriendly.
Almost all succulents are remarkably easy to propagate from cuttings or by division. In the wild, pieces of prickly pear cactus that fall onto the ground will begin to develop roots through the rainy weather of autumn and winter, and be ready to grow into new plants by spring. In the home garden, cactus cuttings should be left out for a week or more so that the cut ends will ‘cauterize’ (Actually, they just dry out a bit.) and be less susceptible to rot once they get plugged into the ground or pots to grow roots. Alternatively, clumping cactus that develop multiple main stems from the base can be divided, although the spines make handling them difficult.
Most aloes and some agaves produce basal shoots known as pups, that can be split from the main plants to grow into new separate plants. Agaves that do not produce pups while young typically start to produce pups after a few (or many) years, as they mature enough to bloom. Many of the larger types produce an abundance of pups after bloom, since the main shoot dies as flowers deteriorate. If desired, one or more of the pups can be left in place or planted back to replace the parent plant.
Most other succulents are even easier to propagate. Small cuttings can be plugged wherever new plants are desired. Some can even be grown from leaf cuttings!