When and where to place plants in the garden is an art and a science. It can be approached analytically based on research and data or in a more intuitive by the feel way. Both are valid. Those inclined towards scientific methods often get stuck in decision making, get boggled down in minutiae, have difficulty finding information concerning specific plants, or become lost in trying to balance and unite all the variables inherent in working with nature. Those who go the artsy route are less bothered by the cumbersome research, but unless they possess experience and field knowledge in addition to their aesthetic tastes, the gardens will flop. Not initially because the artsy person will ensure that the garden will look pretty nice right off the bat, having just picked whatever looks good at the nursery at the moment. It is time that will reveal the character of the garden. That is to say the plants may end up crowded and unhealthy, dangerous by way of mature spines or poisonous saps, and in the end ‘ugly’ because not much thought has been applied to the plant palette growing up together as a garden community. Spacing, root room, shading, weeds and maintenance all play a part in such outcomes. A garden grows and changes in a dynamic fashion and that is its greatest joy. It is not a static picture or arrangement composed for one day of installation. It takes continual hands on human commitment and work if it is to persevere and be happy.
On the analytical side, consider the plants first. In spite of what the designer or landscape architect depicts on the plan, it is hard to predict how big the plant will be in five years or ‘at maturity’. Some plants just keep on growing and do not stop at 5’ diameter by 12’ height simply because somebody wrote that down in a reference text or drew a circle on a piece of vellum. Every plant has a particular growth rate and some get bigger faster, some take forever. For example in our region, the woody perennial Lavatera and the butterfly bushes Buddleia are fast but the Daphne is slow. A dwarf conifer is still three feet tall in fifty years. Also consider the plant’s way of growing and its natural shape. The hummingbird sage Salvia spathacea spreads sideways rhizomatously and may form a nice mat for you over time, but it is uneven and haphazard depending on where the stems decide to pop up. The seaside daisy Erigeron glauca is relatively well behaved, and does make a groundcover about a foot tall or less. And, you can prune it to your liking. A plant with closely planted neighbors often behaves differently from one with ample room to spread out. They are each individual and unique in their approach.
The plants do not grow in isolation or have set patterns that they adhere to. Their size and shape are dependent on the particular garden conditions of sun, water, soil, and wind. All interplay and are dependent on one another. Not enough sun and the plant may reach out farther and farther looking for it and have a floppy leggy look that ‘wasn’t in the catalogs!’ Too much sun and the shade loving plant may get the burned up leaves that have you calling the plant pathologist. Too much water and the plant may rot and drown and get sick with fungal disease, and too little water may cause the plant to become drought stressed, stunted, and not want to grow. Rock or sand? With manure or without? It goes on like this endlessly. There is a range that plants enjoy and are comfortable in, where they seem to sing and flower and hum laughing tunes. There is another range where they are in survival mode, hunkered down, wishing for a killing frost or a typhoon to take them out.
So assuming you figured out and calculated the growth rate, precipitation rate, percentage of sand clay and silt, parts per million of zinc and nitrogen and sulfur, gallons per minute of the variable rate nozzle, hours of daylight and the shade cast by surrounding buildings, the cation exchange rate, and so, there is still the matter of the nursery.
So somehow with the help of computers and scientists everywhere you have drawn up a plant list of the ‘perfect plants’ for your garden. It is based on careful analysis of existing site conditions. You have a plan using three-dimensional simulations which show the garden growing and fading through time, the angle of the sun, the tall plants in the back and the low plants in the front. Everything exactly as you have wanted and planned it. Not a thing out of place or random or unexpected. Good. At the nursery you hand them the plant list and they are like no we don’t have that cultivar you want twenty of. The other plant you want they say we have it only in five gallon plants not one gallon plants. Another plant which the computer said is perfect for our region the nursery says no way we don’t grow that anymore because it was a carrier for this or that disease. Your choice specimen plant in a two-foot box is sold out. You are like “what!’ I gotta go back to the drawing board and redo all my plants!
Then there are the little analytical decisions at the nursery. Do I plant the small four inch pots or the big five gallon pots? Well they say the little plants will grow up fast in a year, and they are cheaper. But the big pots look good, right away! But what will happen in a year, two years, five years down the line?! Do I buy three mud flats of the groundcover, or twenty one gallon pots? My reputation as a designer is riding on this one! Help! And we have not yet even talked about client expectations, aesthetic preferences, and the finicky fashions of horticulture trends… So a strict analytical methodology is not only disconcerting and confusing, it is downright impractical for the landscape designer. Sometimes the pay sounds good but if you calculate the hours?! The mental stress and anxiety?!
Another way to approach this whole project is by feel and flow. Intuition and imagination. The fiction foil to the nonfiction data and information saturated reality. I suggest that you visualize a mythical animal that lives in your garden space. See its innards and body parts. It is a vertebrate animal, by the way. So for the pieces of back bone, the vertebrae, you find a plant that some old timers called the structure or the bones of the garden. It can be herbaceous or woody, monocot or dicot. But, it has to work. For that spot in the garden. For that neighborhood. For that part of town. For that part of the country. It should be a good looking plant, a proven performer, a plant the nursery actually has. It may be a dependable bloomer eight or nine months of the year, it may have colorful foliage or cool texture and shape. It has to work. So if everything in the garden sucks, the bones hold up. When other plants are dormant or tired or shredded and haggard, this plant is still there, taking care of business. So you lay out this plant in an animalian flow pattern in the garden. Your mythical animal might be a sea snake or dragon, or a griffin stingray, whatever. The vertebra don’t all have to show, since the sea snake goes above and below ground in an undulating pattern. In some cases it might even be two species of plants that serve as the backbone. It is okay.
Then you put in a plant for the head of the mythical beast. That in design circles may be called the focal point, in the nursery the specimen plant, and so on. Maybe the beast has two heads, so two crazy cool plants. If you happen to dream of a hydra then you will have a crazy mind blower of a garden like the entrance garden to the San Francisco Botanical Garden but for most gardens that is overkill. Like looking at a movie awards ceremony of dressed up peoples everyday. The beauty in a small garden lies in the occasional kabamm spaced out in time, not constant stimulation.
Then, having the head and the bones, it is time to fill in the muscles and sinew and tendons, the appendages if any, the skin and colors, the internal organs and the frills of feathers and fur, iridescence and rough folds. Any number of smaller shrubs, herbaceous perennials, bulbs and corms and tubers, annuals, vegetables are all excellent. For most clients six or eight plant species in a small San Francisco residential yard is sufficient. If they are gardeners they appreciate diversity and understand complexity. But if they are not gardeners, many plant species stuns the client and causes them to lose their bearings and you to lose the design job. Remember it is a mythical creature you are working with. So it may have fins or legs, wings or a long slimy tail. What this means in horticulture language is that you may have a long swathe of daffodils in yellow and white, with a pair of rockroses and lavenders anchoring the northern slope. A set of manzanitas and sages on the eastern flats. The mythical creature may have a belly that lights up with colors in the spring and summer evenings. That, in garden tongue, is the field of four o’clocks or Iceland poppies at the entrance to the garden.
Knowledge of information and its limitations, pushing gardening boundaries and making mistakes, and a magical framework are all important to consider in plant selection and placement. To combine the workings of art and science in the garden is the challenge. The best designs grow out of field experience and careful observations of plants in their habitats. For this, it is essential that good designers garden religiously, hike and wander profusely, and are patient as they meditate on nature through time. Do not fret and worry about the little decisions in the garden. Plop ‘em in and see what happens! Most importantly, enjoy the trees and learn as the years stream by. Good luck in your plant adventures!