With its short days and cold temperatures, January is a good month to turn your focus to indoor gardening and expand upon your houseplant palate. It is a wonderful way to bring the garden indoors, so to speak. However, simply because the plant is labelled as a houseplant does not mean it cannot go outside come next summer! Haworthiopsis is a succulent that my mother propagated and distributed throughout the house and summer garden with great abandon, but it never garnered much of my attention. Having now ‘inherited’ all of these plants, I have come to discover its beauty, along with its wonderful care free nature!

Haworthiopsis was originally described and placed under the genus Aloe by Carl Linnaeus (1707-1778) in 1753 and was classified within the Liliaceae or Lily Family. It has recently been relocated under the Asphodelaceae or King’s Spear Family. The genus name was changed from Aloe to Haworthia in 1809 by the French physician and botanist Henri August Duval (1777-1814). The genus name honors the English botanist and entomologist Adrian Hardy Haworth (1767-1833) who described 21 species of the genus throughout his career, although he too classified them as Aloe! In 2013, based upon genetic studies, the British botanist Gordon Douglas Rowley (1921-2019) split the genus creating the new genus of Haworthiopsis. The new ending for the name is from the Greek Ópsis for appearance, indicating these plants appear like Haworthia. The most noticeable physical difference is the thicker and harder epidermis or outer covering of the Haworthiopsis leaf when compared to Haworthia. Both Haworthia and Haworthiopsis are native to countries in the southern regions of Africa with the predominance of species found in South Africa, although Mozambique, Swaziland and Namibia are also home to numerous species. Both genera exhibit CAM or Crassulacean Acid Metabolism whereby the leaf stomata open only at night to reduce the loss of water during the day and allow for gas exchange. This allows the plant to be very efficient at conserving water, but also rather slow growing since it can only produce a limited amount of sugars per day based upon the amount of CO2 absorbed at night.

The most commonly grown species, and the plant my mother used with seemingly reckless abandon is the Zebra Cactus or Haworthiopsis attenuata (pictured at right). The species epithet is from the Latin Attenuatus meaning diminished or lessened and refers to the form of the leaf, which tapers or diminishes to a sharp point. The common name of Zebra Cactus comes from the ornamental bands of small white warty projections called tubercles on the back sides of the dark green leaves, which with a touch of imagination resemble the markings of a Zebra. The tubercles allow the expansion of the leaf during the moister summer months without imparting any tearing or damage to the stiff epidermis of the leaf. The plants are stemless and produce 3-6” diameter rosettes of foliage that develop offsets or pups over time and eventually develop into sizable colonies. White to soft pink flowers are occasionally produced during late fall and winter, which corresponds to the spring and summer months in the plants native homeland. The genetic clock does not change simply because the plants are now in North America! The flowers are located along slender stems that bend like fishing poles under the weight of the flowers. The flowers actually consist of tepals, whereby the petals and the leafy calyx look identical and they are displayed in a bilobate arrangement, with a very distinguished upper and lower lip, as seen above. The tip of the lips reflex back, giving the flower a very pronounce appearance similar to a set of puckered lips. Green or reddish brown stripes run down the inside and outside of the flower and most likely serve as nectar guides or visual cues for visiting pollinators.

Another very ornamental species is Haworthiopsis limifolia, commonly called the File Leafed Haworthia or Fairies Washboard. Herman Wilhelm Rudolf Marloth (1855-1931), a German born South African botanist and pharmacist, described the species in 1910, under the genus Haworthia. The epithet is from the Latin limo, meaning to diminish or file off, a reference to file-like appearance of the raised linear ridges of tubercles along the leaves. The common name of Fairies Washboard is also a reference to the raised ridges of tubercles. The leaves are arranged in stemless rosettes, although they are slightly broader, especially near the base when compared to its previously mentioned cousin. ‘Spider White’ (pictured above) is a relatively recent introduction with very white tubercles and is the recipient of the 2015 Dutch ‘Glass Tulip’ award for best new houseplant. The tubercles are a very showy white and give the foliage a very attractive creamy glow!

Not all the species form rosettes of foliage, as some have stems reaching up to several inches long. Haworthiopsis coarctata bears a central stem that grows to nearly 8” long with tightly clasping leaves appearing radially around the stem. The species was initially described by Haworth himself in 1824 and the epithet is from the Latin for crowded or close together, describing the densely overlapping nature of the foliage. The tubercles appear as linear dots along the length of the leaf and are not as distinctive as in the previous two species. In shade, the foliage is a dark green, although the foliage often turns to purplish-red in full sun, as seen in the image below at Chanticleer Garden. Interestingly, this species is the type species for the genus, although it looks quite different from those forms that create rosettes.

Haworthiopsis species are exceptionally easy plants to grow, providing you do not equate weekly watering with proper plant care! During the summer months, the plants are actively growing and are tolerant of our summer rainfalls, allowing them to be used in summer container arrangements or simply set outside for the summer. In the regions where they are native, they typically grow in the shadow of a rock and prefer a similar, lightly shaded location as an ornamental. Fertilize with a half dilute houseplant food that has a higher phosphorus content, such as 5-10-5. Come fall bring the plants inside and give them a windowsill with bright light or morning light. The key in winter is to let the soil dry out completely in-between watering, which can mean upwards of 2-4 weeks without the need for a watering can – something that may prove very difficult for some gardeners!

As you enjoy the warmth of your home this January, hopefully planning additions to your outdoor garden for 2021, it is always nice to enjoy and add some new houseplants to your indoor garden. There are many plants that ask for so very little, yet provide interest and joy throughout the season. Haworthiopsis is one such genus that will continue to provide joy not only throughout the year, but from one generation to the next!

Bruce Crawford
Program Leader in Home and Public Horticulture, NJAES

December is undoubtedly best known for the Holidays, family gatherings and festivities that invariably include decorating the homestead with colorful plants. The plant most frequently used of course is the Poinsettia. I like Poinsettias, but for the past few years I have been discussing plants that provide holiday cheer while continuing to improve in size and appearance as the year to come, or better yet the years to come, pass. One group of plants that I have greatly enjoyed as colorful houseplants are species of the genus Peperomia, commonly called Radiator Plants.

Peperomia is in the family Piperaceae or Pepper family, which derives its common familial name not from peppers we eat as a vegetable, but from Piper nigrum, the source of black pepper! The genus Peperomia consists of nearly 1,000 species, most of which are found throughout tropical regions of South America, although a few are located in Africa, Mexico and the Caribbean. The genus name was penned by the Spanish Botanists Hipólito Ruiz López (1754-1816) and José Antonio Pavón Jiménez (1754-1840) in 1794, following their 3 botanical tours of Peru and Chile during 1777 and 1788. The name Peperomia comes from the Greek Pipéri for pepper and Hómoios for resembling or similar, once again a tribute to its distant cousin Piper nigrum. The common name of Radiator Plant was coined by the famed horticulturist Liberty Hyde Bailey (1858-1954); since the plants enjoy warm air and bright light, much as one would find on a window sill above a radiator, he deemed it apropos! For nearly all species of the genus, the foliage provides the primary ornamental appeal, although the flowers are intriguing. The horizontal rows of small flowers are located along a 2-5” long spike (image at right) that emerges from the apical tip of a stem. They are certainly not stunning, but they do provide a touch of interest. Very little research has been conducted on the flower pollination, but it appears many of the plants produce seed asexually via agamospermy, whereby unfertilized ovules yield viable seeds!

One of the easiest species to grow is Peperomia obtusifolia, commonly called Blunt Leaved Radiator Plant or Baby Rubber Tree. The species epithet comes from the Latin Obtusus for dull or blunt and Folium for leaf, providing the foundation for one of its common names. Originally described by the German botanist Albert Gottfried Dietrich (1795-1856) in 1831, this native of Mexico and the Caribbean has 1-2” glossy round leaves that appear along stout stems. The plant produces a low, almost shrubby habit, growing to 18” tall by 2’ or greater in diameter. The stems are somewhat brittle and care should be exercised when handling. For December, the form ‘Variegata’ sports attractive creamy white and soft green variegation. Interestingly, there are several forms of ‘Variegata’ on the market. Some have a broad, creamy white margin with an irregular, silvery green central splash that nicely compliments the deep red color of the younger stems (as seen on the left). Others have mottled white and green foliage that is somewhat less impactful yet still very attractive. Regardless, these forms provide great colors for the season.

Another easily grown species is Peperomia clusiifolia, the Red-edge Peperomia. Originally named Piper clusiifolia in 1789 by the Dutch Chemist, Doctor and Botanist, Nicolaus Joseph von Jacquin (1727-1817), it was not until 1829 that the British systematic botanist William Jackson Hooker (1785-1865) properly described the plant. Native to the West Indies and Venezuela, the species name describes how the leaves are similar to the tropical genus of woody plants Clusia, which was named after the famed Artois botanist, Carolus Clusius (1526-1609). The plants have thick waxy paddle shaped leaves, growing to 3-4” long with a prominent red margin and red stems. The variety named Tricolor (pictured at right) features foliage splashed with red, white and green, producing a most attractive plant for the home that can be paired very nicely with some Poinsettias! As with the previous species, plants reach upwards of 18” tall and gradually spread to 18-24” around.

The most commonly grown Radiator Plant is Peperomia caperata. The origin of the plant is actually unknown, since the botanist Truman G. Yuncker (1891-1964) described the plant in 1958 from a plant in a private collection. The species name is Latin for wrinkled, which very aptly describes the deeply veined and corrugated foliage. There are a number of dark purple and green foliaged forms, but one of the most handsome for December is ‘Silver Ripple’, with almost reflective, silvery foliage between deep green veins (pictured below).

Most species of Peperomia are epiphytic, dwelling in tree tops where they are exposed to brighter light than on the ground below. They grow on decaying branches or composting leaf litter trapped amongst the base of branches. As a result, they prefer well-drained potting soils that are rich in humus and kept on the drier sides, especially during the winter months. In fact, Peperomia caperata develops decay if the crown remains wet and benefits from the pot being placed in a container of water, allowing the water to be absorbed from the base, keeping the crown dry. P. clusiifolia and P. obtusifolia are much less fussy, although they too benefit from the soil being kept drier during the winter when active growth slows. All species prefer warm temperatures and should be kept away from cool drafty windows where the ambient temperatures could dip below 55°F. Although not a necessity, increasing the humidity does benefit the plants. If space allows, setting the pots on top of gravel in a shallow dish flooded with water will increase the humidity. Also, just because the plants are listed a ‘houseplants’, it does not preclude them from being used outdoors come the summer – a mistake made by many a gardener! In late May, place the plants outside in a lightly shaded area, where our humid warm summers will encourage lush growth.

Peperomia will certainly not replace Poinsettia for its seasonal color. However, Peperomia does provide a colorful and enduring plant that will only increase in beauty with the passing of the years. Happy Holidays to all!

Bruce Crawford
Director, Rutgers Gardens

Let’s face it, November is not a month best noted for flowers. The spectacular fall colors of various trees and shrubs abound, but for the pollinators, there are scant few flowers left to visit. Even most of our native plants have succumbed to the autumn frosts. However, over the past few years, I have noticed one plant that has sustained both blooms and pollinators well into November – Aster tataricus, commonly known as the Tatarian Aster.

Aster tataricus is native to the cold regions of Siberia, Northern China, Mongolia, Korea and Japan, where it is native to moist meadows and wetlands. It is a member of the Asteraceae or Sunflower family, which contains close to 32,000 species. Carl Linnaeus (1707-1778) first penned the genus name in 1753 from the Greek Astēr for star, referring to the star-like form of the flowers. Linnaeus established Aster amellus, the European Michaelmas Daisy as the type flower to which all the other plants for this genus are referenced. Initially home to an enormous number of species, the genus was reduced to around 180 species found throughout Eurasia, based on more recent and improved understanding of the genetics. Carolus Linnaeus the Younger (1741-1783), continuing in his father’s footsteps, published this species in 1781 in his book Supplementum Plantarum. The species epithet tataricus comes from Tartay, an archaic name for the geographic region that extended from the Caspian Sea and Ural Mountains east to the Pacific Ocean, including the areas to which this plant is native.

Aster tataricus is a robust plant, to say the least. The coarse, paddle-like shape of the foliage always reminding me of Horseradish with the basal green leaves reaching 16-24” long and up to 6” wide (pictured above). The plants are rhizomatous in nature and can spread over a fairly substantial area of the garden, providing a rather pleasing yet coarse groundcover. In late August to mid-September, the flowering stems elongate, reaching an impressive height of 5-8’ before blooming! The stems are hispid or clothed with straight bristly hairs along with more modestly sized leaves of 3-4” in length and 1” wide. The top of the flower stem branches freely, producing abundant flower buds that open from late September through early November. The flowers (pictured at right) typically have between 12-18 lavender-blue to blue ray florets that resemble petals, surrounding a center of yellow disc florets, creating a beautiful display.

The Aster’s stems are very sturdy and unless the plants have been excessively fertilized, they do not need staking. Although the traditional thought would be to place the plant at the back of the border due to the height, the plants also look great when worked in among grasses such as Calamagrostis x acutiflora ‘Karl Foerster’ (Feather Reed Grass) that typically matures to 5’ tall (pictured at left). The blue flowers peaking above the grassy foliage, providing a very natural appearance similar to their native meadows. The flowers also have great symbolism. Hanakotoba is the ancient Japanese art of assigning a meaning to a flower, which in turn allows a person to communicate with others without any spoken words. ‘Flower talk’ so to speak! Aster tataricus expresses remembrance, a tribute I suspect due to its late blooming nature!

If the species form is a bit too tall, the selection named ‘Jindai’ grows to a more controlled height of 3-4’ tall. Rick Darke of Longwood Gardens and Sylvester ‘Skip’ March of the U.S. National Arboretum discovered this selection at the Jindai Botanic Gardens in Tokyo Japan during 1985. Although shorter in height, they are still spreading in nature and need to be watched to ensure they do not grow beyond their bounds by removing unwanted rhizomes early in spring. I have also found this habit to be a benefit, since the plants will spread into neighboring shrubs and create some attractive combinations. In one instance, as pictured at right, the Aster has spread amongst a Bonica® Shrub Rose and the sky blue flower of the Aster looks great growing amongst the soft pink flowers of the Rose! It has also spread into a Salix alba ‘Britzensis’, commonly known as Coral Bark Willow that is coppiced or pruned back to 8-10” annually. The stems of the Willow develop a light red coloration by mid-October, providing a nice backdrop for flowers. Another pleasant combination is with Amsonia hubrictii, the Blue Star Amsonia; the yellow fall color of the Amsonia pairs beautifully with the central yellow disc flowers of the Aster, as seen in the image below. So many combinations!

Both the cultivar ‘Jindai’ and the straight species produce copious amounts of nectar late into the season and are beneficial to a number of pollinators, including bees, beetles, moths and wasps. The plants are best grown in full sun in moist to average garden soil. As I have discovered, they do require more acidic soils and fail to perform well in soils with a high pH. Other than occasionally rogueing out some rhizomes that have ventured too far afield, Aster tataricus is very low in maintenance and truly is one of the ‘Flowering Stars’ in the November Garden.

Bruce Crawford
Program Leader in Home and Public Horticulture, NJAES