Enclose, Define, Edge, and Carpet
After you have drawn your base map, included the necessary circulation ways, and determined where the trees will be located, you can start building patterns and definition to your design with shrubs. A good, logical way to do this is to design with shrubs by height category. By incorporating shrub masses by size, you can delineate enclosure and screening to build outdoor rooms within the site. You can establish living mulch areas. You can build color blocks with contrasting backdrops and create multilevel echoes of color that excite the viewer. You can hide naked stems and hide messy plant beds. You can prevent maintenance burdens. You can open views. Categorizing shrubs by size is a really handy tool for landscape design!
Shrubs are offered for sale in containers, sized in four-inch pots, gallons, 3 gallons, 5 gallons, and 7 gallons. These plastic containers are in no way indicative of the final size of the shrubs you purchase. They only determine your cost. In fact, the perfect shrub for your project usually costs exactly the same as the worst shrub choice possible, as long as they both are offered in the same sized container! What counts is the mature size of a shrub. Mature size counts more than any other yardstick you use in deciding what to plant. So, categorize your shrub choices by full-grown height rather than purchase size.
Start with tall shrubs. These are shrubs greater than six feet but less than fifteen feet tall. Anything taller might be considered a tree. Tall shrubs create enclosure and provide a backdrop for the rest of the vegetation. They are rarely practical for foundation planting, unless placed at the corners of a building or in front of tall, blank walls. Because of their size, they block views, so they make great choices for screening or enclosure. One reason you see tall shrubs offered for sale more than any other size is because they are so interesting! The tall shrubs typically provide lots of form, flower, and fruit choices.
There are some famous families in the tall shrub category—Viburnums, some Junipers, some Loropetalums, PeeGee Hydrangeas, Sasanqua Camellias, Crapemytles, Waxmyrtles, Osmanthus, Chinese and hybrid Hollies, Arborvitaes, Old-fashioned Azaleas, native Azaleas, Rhododendrons, Pittosporum, Inkberry, Mahonias, Pieris, Quince,Lilac, Firethorns, Oleander, and lots of the heirloom shrubs used in the Victorian when houses were lofted up on tall foundations like Beautybush and Pearlbush. Privets fall into this category, too, but they can become very invasive. Tall shrubs have been around for a long time, so in each of these families there are hundreds of cultivar choices. It’s not important that you know them all. Just choose within the family, and you should be safe. You can mix and match these families in a hedge or group, but think through the final effect rather than peppering too many species on a plan. Simplicity is elegance.
You can more effectively mix and match shrubs by layering a new, staggered row of medium shrubs in front of tall shrubs for a contrasting look. Medium shrubs are three to six feet tall. These can be used as foundation plants or as facer plants for taller shrubs. They are not suitable for areas where clear sight lines are needed for pedestrians or vehicles. The densest part of medium shrubs is right at eye level, so they block views. If you are designing an area on a human scale, people will feel comfortable with this size. These are shrubs you can pat on the head, and you can reach the limbs to prune them if necessary. They are a moldable, manipulate-able group. Small-leaved evergreen species are perfect for topiary. Boxwoods, hybrid Azaleas, Aucuba, Spiraeas, dwarf Hollies, dwarf Loropetalums, Nandinas, Cleyera, Yuccas, Dwarf Palmettos, Hydrangeas, Barberries, Sweet Box, dwarf Inkberry, Burning Bush, dwarf Laurels, Dwarf Yews, Sweetspire, Clethra, Pittosporum, Indian Hawthorn, Gardenias, Weigelas, Butterfly Bush, Abelia, Roses, Forsythia, and Mountain Laurels fall into this category. Ornamental grasses can be considered part of the medium shrub category, as far as design use is concerned. The tall ornamental grasses grow into thick masses, and the shorter ones tend to from small clumps. Use medium shrubs in masses of at least three or more. As tempting as it is to use them under windows, do not. You will be committing yourself to pruning year after year, and most likely ruining the natural form of the shrubs.
Under windows your best bet is low shrubs. Low shrubs are one to three feet tall. It’s a surprisingly limited category, considering the potential market for foundation shrubs. Keep your choices under windows limited to shrubs that will never outgrow the space, even if your choices are reduced. You can get some really effective compositions using low shrubs in groups of nine or more. Low shrubs can be used to create a tapestry of foliage color. They enhance the edges of landscaped beds and provide a definitive boundary for geometric shapes in the garden. They make wonderful facers for parterres. They hide, or at least, minimize the messy litter and unkempt areas beyond their clean lines. Dwarf Boxwoods, dwarf Hollies, Weeping Hemlock, St. John’s Wort, big-leaved Sages, Santolinas, Lamb’s Ears, low Junipers, dwarf Nandinas, dwarf Abelias, dwarf Cephalotaxus, Holly Ferns, Cast Iron Plant, dwarf Spiraeas, Gumpo Azaleas, Cotoneaster, low Loropetalums, and Crimson Pygmy Barberries fall into this category. Geometric plant beds can be pretty messy as long as they are bounded by a low hedge of English Boxwood.
What if you want to actually carpet an area of your site, without resorting to turf grass? Your options expand considerably, then. Ground covers can be woody ornamental shrubs or herbaceous perennials. Pachysandra, Green and Gold, Candytuft, Crown Vetch, Creeping Fig, Yellow-root, Lantana, Sedums, Creeping Gardenia, low Junipers, Epimediums, Thyme, Thrift, Liriope, Mondo Grass, Blue Rug Juniper, Heath, and Procumbens Juniper fall into the ground cover category. Some herbaceous perennials do a good job of being a ground cover—Dianthus, Mints, Oregano, low Sarcococca, Hellebores, and Tiarella work nicely. Some ferns provide good ground cover, also. Notice, I didn’t mention English Ivy or Periwinkle? They are simply too invasive, unless corralled by a planter. If plants are vigorous enough to carpet the ground, they may also be invasive. Take care with your choices!
There are a lot of plants that you might be tempted to consider for ground covers, but which don’t really provide a thick, carpeting effect. They need to be used in only small areas. Low woodland plants typically grow in tiny clumps and will not provide adequate, dense cover. Other plants don’t provide cover year-round in a reliable way, and may go dormant and disappear during the winter. Be sure to consider what ground covers will look like in every season.
Spacing for ground covers can vary quite a bit. Some low junipers can stretch eight feet while some tiny herbs can only fill small nooks and crannies.
So, enclose, define, edge, and carpet with all the choices above! Did I leave out a major selection? Let me know what essential selection has worked for you in your projects.