In recent years, as interest in herb cultivation has increased, more gardeners are discovering the decorative possibilities of plants that have been carefully trained and trimmed into ornamental shapes. Container-grown herb topiaries can graciously frame an entryway or decorate a table or windowsill, and generally enhance decor, whether indoors or out. The time and effort spent in maintaining one of these green sculptures are repaid in the charm and beauty it brings to a room or garden, and sometimes also in the culinary dividend of its trimmings.
Most topiaries are produced from upright-growing woody herbs such as Greek myrtle (Myrtus communis), rosemary (Rosmarinus officinalis), lemon verbena (Aloysia triphylla), fringed lavender (Lavandula dentata), dwarf sage (Salvia officinalis ‘Nana’), and sweet bay (Laurus nobilis). Small-leaved scented geraniums (Pelargonium spp.) also offer many possibilities.
Topiaries begin their careers as cuttings, except for the occasional mature plant discovered to have a central straight stem. Successfully rooting cuttings of woody herbs requires a certain amount of skill and patience. If you’re considering rooting your own cuttings, see “Growing Herbs from Stem Cuttings.” However, the easiest way for a novice gardener to obtain suitable cuttings is to purchase them, already rooted, from a reliable nursery. Look for a plant with a single, very straight stem and no side growth. I’d suggest that you start with one in a 3-inch pot. If you are ordering by mail, mention that you want to make the plant into a topiary.
Training Topiary Standards
Training begins early for rooted cuttings that are destined to become topiaries. The first step is to transplant the young, 3- to 4-inch-tall plants from the rooting medium into 3-inch pots. Choose a potting mixture that drains quickly, such as Pro-Mix, a soilless mix, or equal amounts of aged compost, sand, and peat. To test drainage, fill a pot three-quarters full of potting mix and flood with water; it should pour out the drainage hole. If water stands, the mix is too heavy. You will need to add perlite or more sand to lighten it.
After transplanting the rooted cutting to its new pot, insert a short, slender, 10- or 12-inch bamboo stake, such as a barbecue skewer, about half an inch to an inch away from the plant. Tie the plant loosely to the stake with one or two loops of cotton string. As the plant grows, add successive loops near the top to keep it growing upright. Some growers instead split a plastic drinking straw down its side and position it around the tender stem in this early stage of training.
A few months later, when the plant has reached the height of the stake and begins to outgrow its small pot, transplant it again, this time to a 5- or 6-inch pot. At this time, replace the original stake with a new bamboo garden stake which is as long as the intended height of the mature tree. Push the stake deep into the pot an inch from the plant’s stem and tie the stem loosely to it at frequent intervals with strips of cloth or raffia (string is not strong enough).
Now is the time to determine the ultimate form of the topiary. Observe the plant’s pattern of growth. Are twigs bunching at one or more points along the stem as well as at the top? It may hold promise of a double- or triple-tier shape. On the other hand, it may suggest a less geometric form such as a fanciful animal or bird.
Single ball. The secret of effective topiary design is simplicity of form and correct pruning. The simplest design is the standard (also known as the poodle or lollipop), consisting of a single head of foliage clipped into a tight ball. Any of the species mentioned above may be trained in this shape, though some are more appealing when allowed to grow into a less formal, naturally open head of arching branches. Either shape is achieved by pinching the topmost growth, or leader, when the plant has grown to the desired height.
Begin trimming the lowest leaves and branches from the stem at the time of the plant’s transfer to its 5- or 6-inch pot. The green head should measure one-third the total length of the stem—1 foot for a 3-foot topiary—for a pleasing, balanced appearance and adequate photosynthesis to keep the plant growing well.
After you’ve clipped the leader and the tips of the side branches, just relax and watch the foliage start to fill in and the head begin to take shape. This process usually takes a few months, depending on which herb you are working with. When the shape has been achieved, maintain it by clipping the new growth as it appears, about every other week during periods of rapid growth in the spring and summer, seldom or not at all in winter. As the plants become large, you may transplant them to 7- or 8-inch clay pots.
Cone. A variation of the single head is a cone, larger at the bottom, beginning at the rim of the pot for a Christmas tree effect—particularly appropriate for an upright rosemary—or farther up the stem. A cone can also top a multiple-tier topiary. These more complex designs require small-leaved, tightly compact plants such as Greek myrtle and rosemary.
Barleysugar. A bit more complex is the form traditionally called barleysugar, in which the shaped head surmounts a trunk which has been wound into a corkscrew. This style of trunk looks best topped with a plain globe of green, for here the focus is on the stem. Select a six-month-old plant and transplant it to a 5- or 6-inch pot. Insert a stout stake—I use 3/4-inch bamboo—into the pot and trim it to two-thirds the height of the plant, leaving the top growth free. Now, carefully wind the still-flexible stem evenly around the stake and tie it snugly in position at several places along the stem. Check the ties in two or three weeks and loosen them as soon as they start to become tight. Trim the leader and side branches as described above for the single-ball design. As the tree grows taller, continue removing the lowest branches and winding and tying the stem around the stake, checking previous ties for tightness.
When the plant has reached the height of the stake and the stem has stiffened somewhat (this can take anywhere from six months to a year, depending on height), remove all the ties and, starting at the top, very gently unwind the stem from around the stake. Pulling the stake out or unwinding too woody a specimen will injure the stem. After unwinding the stem, support the topiary with another stake the same thickness as the trunk. The spirals should look evenly spaced. As the trunk thickens with age, the spirals become less prominent and more subtly wavy. Nothing can equal a matched pair of these elegant topiaries stationed at a formal entranceway, on a patio, or in a sunroom. I have made barleysugar topiaries with 3-foot-tall Greek myrtles and plan to experiment with ‘Lemon Crispum’ scented geraniums.
Topiary plants may be trained on circular or heart-shaped wire rings as well as more elaborate and fanciful forms. I’ve used ‘Lockwood de Forest’ and ‘Huntington Carpet’ prostrate rosemaries as well as the small-leaved ‘Prince Rupert’, ‘French Lace’, ‘Lemon Crispum’, and ‘Strawberry’ scented geraniums for these forms.
To form a single wire ring for a 4-inch clay pot or other container, bend a 23-inch length of aluminum wire the thickness of a coat hanger around a 6-inch cylinder (such as the top of a clay pot), twisting together the excess wire at the ends. Stop twisting about 1 1/2 inches from the ends and, with pliers, bend them out sideways as shown. Suspend the ring on a rod such as an old broom handle and spray paint it a light sage green that will blend with the plant stems. When the paint is dry, stand the twisted stem of the ring in the pot. (For a larger pot, make the ring at least as wide as the width of the pot.) Partly fill the pot with fast-draining potting medium and tamp it down to keep the ring upright. A heart shape is formed by simply bending a single ring downward at the top before placing it in the pot.
Select a rosemary or geranium plant having at least one long branch—preferably two or more—and place it in the pot right next to the ring. This could be a recently rooted cutting, but even a mature plant in a 6-inch pot can be shaped in this way.
For a plant with just one branch, start at the bottom of the ring winding the branch around and up one side; secure it loosely with green cotton string. It will eventually grow all the way around the circle. Emerging side shoots may be pinched to make the ring of foliage bushier, or a side shoot near the base may be left to grow and tied onto the other side of the ring.
For a multibranched plant, train the branches up either side of the ring and pinch the side shoots to encourage bushiness.
When the plant has grown sufficiently to extend all around the ring (a matter of four to six months for a rooted cutting, less for a more mature plant), clip the branch tips to force further branching and thicken the shape. To discourage fungus diseases, keep your ring in full sun with good ventilation, and when watering, avoid splashing the leaves. Continue close trimming as the plant grows.
Rosemary rings especially offer mealybugs a tempting haven. A thorough drenching with an insecticidal soap such as Safer’s will eliminate them if they are detected early. Follow the directions on the container. Alternatively, mealybugs may be removed with cotton swabs soaked with alcohol. Oil sprays are effective in eradicating these pests from some species of plant but are lethal to rosemary and lavender.
Light. Herb topiaries need full sun to look their best. They can be kept outdoors in summer as long as they are thoroughly drenched every day during hot, windy periods. Most plants that I grow are not winter-hardy where I live in Maryland and must be moved indoors to the sunniest spot available before first frost. I rotate the pots one-quarter to one-third turn each week to expose all sides to the sun when they are indoors.
Soil. Topiaries appreciate soil that is light, porous, quick draining, and not too rich. Most herbs thrive in neutral soil, but lavender prefers a somewhat alkaline growing medium. Pro-Mix potting mix may be used or a homemade equivalent of three parts potting soil to one part sand or perlite, plus a sprinkle of agricultural lime.
Water. If a pot feels light when you pick it up compared to how heavy it feels when wet, and if the surface of the soil is dry and the soil ball is beginning to shrink away from the sides of the pot, it’s time to water. These judgments take practice but are worth developing. Topiaries grown in containers too large to test by lifting should be checked with a house plant moisture meter. Any reading less than 50 percent calls for watering. Thoroughly drench the plant every time you water, but never allow the pot to sit in the drainage water. A soil mixture that drains well (described above) is essential to prevent root rot. At the same time, you must keep the plant from drying out completely. As you become familiar with the plants you are growing, knowing when to water will become second nature.
Fertilizer. For maximum rapid growth, which permits optimal trimming and shaping, I fertilize topiaries with a weak liquid fertilizer every two weeks during the active spring and summer growing season. Peters water-soluble fertilizer for foliage plants is good, as is fish emulsion. Reduce the frequency of feeding as growth slows, and don’t feed at all if the plant stops growing during the winter.
Pruning. Regular pruning is necessary to maintain the shape of a topiary. During periods of rapid growth in spring and summer, you will probably need to trim it every other week; in winter, rarely or never. Use wide-handled “rabbit ear” shears, curved-blade pruners, or ikebana shears.
Trim around the bottom of the plant first—new twigs often turn downward there, especially on rosemary—and work up the sides to the top. Cut twigs of large-leaved plants such as bay close to a leaf node, but simply trim smaller-leaved plants “haircut” fashion. Branching points don’t matter on these, but cut big plants above a “Y” on a branch to stimulate further branching and filling in.
Herb topiaries require more time and commitment than most potted plants, but they reward one with more than a handsome accent for the living room or patio. They provide an opportunity to pay close attention to a plant’s habits and needs, to master important skills by practicing them on a small scale, and to respond creatively to the materials nature gives us to work with.
— Sally Gallo fled the business world in 1986 to learn the world of plants at Bittersweet Hill Nurseries in Davidsonville, Maryland. In time, she became responsible for a veritable forest of perfectly shaped herb topiaries. Her book, Herb Topiaries, was recently published by Interweave Press; this article is excerpted from it.