Most people, especially city folks, seem to be suspicious of any plant that dares to grow higher and wider than a marigold. Trees may be exempt; nevertheless, they are usually grown in isolation surrounded by plenty of short, safe turf.
Large plants—be they trees, shrubs, or large herbaceous perennials—too often are at the mercy of homeowners’ loppers. Why anyone would prefer a naturally graceful, billowing bridal wreath trimmed into the shape of a light bulb remains a mystery to me. Tall and bulky herbs suffer a similar fate.
Many gardeners apparently prefer tiny borders no deeper than 2 or 3 feet. Perhaps they believe that a shallow border will be easier to manage. There’s plenty of room for smaller herbs such as basil, calendula, chives, and thyme, but a big one—perhaps angelica or Joe-Pye weed—will look like Gulliver among the Lilliputians. No wonder it gets hacked backed mercilessly in a vain attempt to make it fit in.
• Chart: Big Plants for a Bold Garden
Room to Grow
A skimpy 2-foot-wide border just can’t produce the dramatic effect you admire in books and magazines. Large beds, on the other hand, open the door to a whole range of plants that don’t fit into tiny, tidy beds. Big borders are made for big plants. I freely mix perennial ornamentals and herbs in my borders; after all, many of the ornamentals have traditional herbal uses. Tansy, yarrow, costmary, globe thistle, bee balm, bugbane (Cimicifuga racemosa), angelica, Joe-Pye weed, monkshood, and plume poppy (Macleaya cordata) need space to be shown to advantage. Even such annuals as sweet Annie, sunflower, lion’s-ear (Leonotis leonurus), tall verbena (Verbena bonariensis), and castor bean can attain the height of small trees in a short time. Tropical plants such as papyrus, cannas, and bananas are blockbusters, even in temperate gardens.
The key to making a successful big bed is to plan for the ultimate size of its inhabitants. This can be tricky as the information on nursery tags seems intended for gardeners in Pittsburgh or Peoria or Paducah, not my semiarid climate, where the drought and cold winters and clay soil limit the growth of many plants. The best thing to do, wherever you live, is to study how a plant grows at a local botanical garden or in your neighbor’s yard before placing that kind of plant in your own garden.
Underestimating a tree or shrub’s mature size is all too common: we’ve all seen houses eaten alive by their foundation plantings. Leave room for the plants to spread and strut their stuff. Shrub roses, for example, begin as scrawny, pot-grown youngsters. For a while, they look like gangly teenagers, but in five or six years, they come into their full glory. Plant light, airy, shallow-rooted annual herbs such as dill, opium poppy, or sweet Annie around shrub roses. Other suitable companions include short-lived perennials such as peach-leaved bellflower, columbine, lunaria, rose campion, and foxglove. As the rose spreads its wings, it will shade out its shorter neighbors, forcing them to reseed farther away from the base. Do the same when situating Carolina allspice, witch hazels, pokeweed, sassafras, dogwoods, lilacs, plums, and hydrangeas.
Put the tallest plants at the back of the border or at the center of an island bed, you’d be surprised to learn how many borders I’ve seen in which some tiny herb at the rear is straining to be seen up front. That doesn’t mean that a few spires of mullein, tall verbena, or foxglove can’t be allowed to seed near the front as long as you can see around or through them to the back.
Use herbs with contrasting shapes. Round masses underscore spikes dramatically. Possibilities include silver tansy (Tanacetum niveum), feverfew, sages, rue, smaller yarrows, and Artemisia ‘Powis Castle’.
Big-leaved plants break up the visual monotony of a bed of Mediterranean herbs, with their short, narrow leaves. Putting rosemary, lavender, santolina, and oregano next to one another is boring—they look too much alike. Instead, toss a few large-leaved plants into the mix for excitement. Sea kale (Crambe maritima), colewort (C. cordifolia), German statice, sea lavender, lamb’s-ears (especially the cultivar ‘Big Ears’), and silver mullein (Verbascum bombyciferum) thrive in the same dryish conditions as rosemary, lavender, and santolina. The architectural spikes and spines of aloes, agaves, and yuccas also contrast effectively with fine-textured foliage. A yucca in full bloom—its tall spikes studded with creamy white flowers—is a grand sight.
Big foliage unfortunately is more susceptible to wind and hail damage than are finer leaves. My garden got hammered three times last summer. Small hail bounces right off, but a big storm can really slice and dice.
Running With The Big Guys
I’m creating a new garden at Denver Botanic Gardens to showcase our lilac collection. Rows of shrubs can be deadly dull so I’m arranging them in cottage garden fashion. Lilacs are big and bulky; the right partners are essential to display them effectively. Plants that bloom in concert with the lilacs as well as later on are vital to my plan.
Lilacs are an important link to the horticultural heritage of my region. Throughout the plains, old lilac bushes mark the sites of homesteads that disappeared long ago. Once they sink their roots into western clay soil, lilacs need only infrequent watering. Their companions in the new garden must enjoy the same conditions. I’m using sea kale, colewort, lead plant (Amorpha canescens), Artemisia ‘Powis Castle’, upright junipers (to pierce the monotony of round green shrubs), silver mullein, native asters and goldenrods, ‘Moonlight’ Scotch broom, as well as yarrows and yuccas. Tough shrub roses also have survived from Colorado’s pioneer days so I’m also planting Rosa xharisonii ‘Harison’s Yellow’, R. ‘Agnes’, R. foetida ‘Persiana’, and R. rugosa var. alba. The color scheme mixes silver and yellow with the colors of the lilac blossoms themselves. For contrast, I’ll throw in a bit of chartreuse foliage from golden feverfew, hop, and ninebark.
A second, lower tier of companions includes sea hollies, globe thistle, daylilies, bearded irises, Phlomis russeliana, silver tansy, and several salvias, including Salvia officinalis, S. forsskaolii, S. pratensis, S. nemorosa, and S. sclarea.
Filling in will be self-sowers such as love-in-a-mist, silver mullein, cream yellow California poppy, white-flowered rose campion, horned poppy, tall verbena, bachelor’s-button, and larkspur. Tulips, crocuses, and alliums will interject color in spring and early summer.
The main part of the new lilac garden measures about 40 by 80 feet—small by public garden standards but large by most homeowners’. I hope that we’ll inspire gardeners, many of whom may have a lilac or two lurking about their yard. By beginning with these lovely, old-fashioned shrubs (or with dogwoods, rhododendrons, mock oranges, or whichever signature plants populate your region) and incorporating big, beautiful herbs and ornamentals into the landscape, you can create an intricate interplay of texture and form that will be interesting to look at throughout the growing season.
In his new position as director of horticulture for Denver Botanic Gardens, where he is responsible for 16 acres of gardens, frequent Herb Companion contributor Rob Proctor will have plenty of opportunity to think big.