Negative space - space not filled by trees, shrubs, stones, or other
elements - is a very important tool in Japanese garden design. This is the
area where appropriate groundcovers can impact the beauty and spirit of
the garden. Here are a few suggestions for low, ground covering and
moss & moss allies.
Explore the countryside in the vicinity where the garden is located. There are mosses and moss-like plants called Selaginella growing in most areas - you just have to find them. You will need to find a species growing in the same light conditions. Pay attention to growing conditions so you can duplicate them as closely as possible.
Dwarf Monkey Grass. This isn't really a grass at all, but a member of the Lily family. There are several cultivars ranging from 2" high to 6", including a dark-leaved variety that comes as close to black as any foliage. Dwarf Monkey Grass, or Ophiopogon japonicus 'Nana', is relatively slow to spread and definitely not invasive. It's dark green foliage color is a good contrast with lighter plants in what is usually a predomanently green landscape.
Turfgrasses . There are some grasses used for lawns that make good groundcovers for Japanese Gardens. My favorite is a cultivar of Zoysia tenuifolia called "Emerald". It has a fine blade and tolerates short cutting to mimic the look of moss. This grass can escape its bounds and become a maintenance problem if not contained by hardscape or at least 6" deep barriers such as steel edging.
Inland Seaoats. This native to creeks and lowlands holds soil on slopes and add grace to streamsides and hillocks. Inland Seaoats or Chasmanthium latifolium grows to a height of 24 inches counting the seed stalks, perhaps too tall to be considered a groundcover. If the abundant seeds are allowed to drop, it can be invasive in moist landscapes.
Ajuga. This is a low groundcover with spatula-shaped leaves of green and purple. There are varieties with large leaves, but I prefer the old small-leaved Ajuga repens. A medium to fast spreader, it is easily controlled.
Wood Violets. More suited to sandy soil with moderate shade and moisture, this Viola species provides a 4 to 6" heigh carpet of medium green, heart-shaped foliage with occasional purple to white flowers.
While the empty space of swept earth, gravel, or groundcovers provides the canvas and horizontal plane of the garden, taller shrubs, ferns and perennials provide the vertical accents and help create spaces and perspective.
Purple sage. A good subject for tamamono with a range of leaf color, growth habit and flower. It is also known as barometer bush as certain selections are dependable forcasters of rain.
Buckeye. Red Buckeye (Aesculus pavia), Yellow Buckeye (A. pavia var flavescens), and Texas Buckeye (Aesculus arguta) are all excellent large bush to small trees for a Japanese garden. The graceful grey to white trunks are crowned by rosettes of palmately compound leaves that emerge at the same time as the large flowerbuds. The seeds are contained in interesting pods that persist on the tree all year.
Mexican Buckeye. Usually a large, multi-trunked bush of 10 feet or more, it can grow to 20 feet. It has pink flowers on its branches similar to redbud, but a little later in the spring. The flowers are followed by provocative, lantern-like seedpods that persist all year, offering an interesting winter sillouette. Ugnadia speciosa.
Mahonia . Also known as Oregon Grape, Mahonia species provide bold, blue-green holly-like foliage with yellow flowers and blue berries. They very in height from 10 to 12" for the dwarf varieties to more than 4 feet for larger cultivars. a favorite for warmer climates is Mahonia bealii or Beal's Mahonia.
Dwarf Barberry . Berberis thunbergiana 'Atropurpurea' is a 10" to 2 foot barbary with cherry red to dark burgandy foliage. This one can be sheared to maintain shape and height, or left to its natural fountain-like habit. It is an excellent visual accent where a splash of color is desired. It does have thorns hidden within its beautiful foliage.
Flame-leaf Sumac. A medium green native, Rhus lanceolata provides a spectical of fall reds, purples and yellows before dropping its leaves in late fall. It normally maintains a height of 4 to 6 feet along the edges of sunny areas, but can reach 15 or more feet. A moderate spreader by running roots.
Rusty Blackhaw. Another native with impressive fall color, Viburnum rufidulum grows from 6 to 20 feet in height.
Possum Haw . As implied by its botanical name, Ilex decidua is a deciduous holly with small medium-green leaves fall leaving clusters of red berries on trunks and stems until the birds discover them as winter treats.
Pittosporum. Pittosporum tobira, known as "Tobira" in Japan is a commonly used Japanese landscape plant. It is adapted well to dry hot climates, can be sheared or trained as an impressive tree with literati qualities. It is available in dwarf varieties such as the popular 'Wheelers'.
Black pines, red pines, and Japanese maples may be considered the quintessential trees of the Japanese garden, but these species may not thrive in some dry and hot climates. Here are some trees to consider as worthy additions to Japanese landscapes.
Blanco Crabapple . Pyrus ioensis var. Texana. Cherry blossom like flowers in spring and cherry-like growth habit to 15 feet. This one is hard to find but worth the hunt. Outstanding!
Carolina Buckthorn. Beautiful glossy foliage and red to black drupe fruit giving an overall appearance of the tropical Coffee tree. Mature specimens are usually 10 to 15 feet but can reach 20 feet with grey to white trunks and branches. Rhamnus caroliniana.
Escarpment Cherry . Prunus serotina subspecies exima is the native black cherry thriving on the inner ledges and creekbeds of the Balcones escarpment and Edwards Plateau where soil and moisture are a little more abundant. Beautiful semi-weeping foilage, pendant flower clusters in spring, beautiful pink to gold fall color and the banded bark typical of this genus.
Mexican Plum. Prunus mexicana is another substitute for flowering cherry for this area. Growing from 8 to 18 feet, it has clusters of white flowers in early spring.
American Smoke Tree. Interesting leaf color and flowering panicles, Cotinus obovatus grows from 8 to 15 feet and offers excellent fall color in good light.
Uvalde Bigtooth Maple. Acer grandidentatum sinuosum Heat-tolerant maple with great fall color maturing at 18 to 30 feet. It gets its name from the large toothed leaves.
Texas Redbud, Mexican Redbud. Cercis canadensis varieties Texensis and Mexicana both do well in dryer climates. The leaves are thick, shiny and dark green. Flowers vary from red (cv. 'Oklahoma') to pink and even white. A medium grower to 20 feet.
Texas Mountain Laurel. Sophora secundiflora grows from 6 to 20 feet tall, usually multi-trunked with dark green compound leaves. The wonderful wisteria-like flowers provide grape-scented purple blossoms in early to mid spring.