I've never actually run across an actual “rule of three” in gardening. The closest I've come is the rule of thumb that says that plants look best if planted in groups of odd numbers – 3, 5 or 7. The rule of threes is my own invention, which is based on the odd numbers rule and then stretched to the limit by my own gardening experience.
Part of that experience was a sort of partial paralysis which comes when most gardeners are confronted with a huge, blank expanse of freshly turned soil where they hope to plant a garden worthy of admiration.
I'll be the first to say that the only admiration that really counts is your own – that if your plants are happy and healthy then your garden will be beautiful. But when it comes to my own beds, I all too often find myself sitting and pondering them and wondering where my design went wrong. To my own eyes, sometimes things seem out of kilter – and that causes me discomfort. I can't just sit and enjoy the garden. Instead I am perpetually popping up to lift one plant from its place to try it in another, hoping to eliminate the problem.
I never have this problem with containers. There I generally choose three plants that go well with each other. They have contrasting textures, one usually being fine, another quite bold and one somewhere in between. One may be upright another mounding and a third trailing. The colors are chosen either for dramatic contrast or a smooth blending of similarity. Three plants, three textures, three forms and my choice of color combinations.
Even when I group containers I have no problem, because I can shuffle them around until they complement each other.
Thinking of that, I realized that I was actually applying a rule of sorts to both my container planting and their grouping. The rule of threes. And I thought – why not apply it to the beds themselves?
We are told to plant in drifts to maximize the impact of each plant in the bed. That means that unless the plant itself is quite huge – like a peony bush, or a small shrub or perhaps a hosta – you plant them in threes. The exception is plants that are really skinny, like a gladiolus or crocosmia, in which case it may take as many as 21 to make any impact Why 21? Why, in fact, the odd numbers rule? Because try as you might, with even numbers you end up planting things in a sort of line or a square. It takes that odd numbered plant to turn the line into a drift. Try it sometimes and you'll see what I mean.
It also takes a mix of at least three forms to create pleasing contrast. Generally I try for an upright plant, one that mounds, and one that trails or flops pleasingly over the edges of the bed. And by the same token, we need at least three textures of leaves to look good (remember – few plants will flower all summer). So I look for plants with fine textures leaves, then some that are more medium, and ideally something quite bold.
I'm not so sure about the rules of three when it comes to flower shapes. Sometimes I try to mix shapes so that I have a daisy shape, a trumpet shape and something that blooms in spires and/or clusters. But I also like the look of similar shapes, as in drifts of coneflowers in white, purple and gold, mixed with white Leucanthemum and perhaps fronted by something short and bold like one of the golden hostas that tolerate sun. So I will leave that and color choices to you.
The trick to using the rules of three in a large bed is to imagine that you are actually planting a series of large containers all placed next to each other so that the colors create the kind of look you like. If you are a misty pastel person then you will plant a series if pale colored “container plantings” with some silvery foliage to help tone down the greens. The only thing to remember is that every few “containers” you will want to repeat something planted in an earlier container. This repetition gives a certain sense of harmony to the overall design. So you may choose to use lavender in several of your imaginary containers, and purple coneflowers in a few others.
For instance, the first area you plant might include a grouping of three English lavender plants. They have a mounded texture and fine foliage with flowers of a beautiful violet blue. Behind them, you might choose a mix of Siberian Iris also in shades of blue and purples, but with spiky, upright foliage and a bolder flower shape. You might choose three white Leucanthemum 'Becky' for the back of the border, because it picks up the white from the iris and has medium textured green foliage.
Moving on to your next grouping, you may want to take a cue from the yellow centers of the Leucanthemum to select three fine foliaged, pale yellow Coreopsis 'Moonbeam' for the front of the border. Like the lavender it has very fine foliage, but in green – and the yellow of the coreopsis will really highlight the deep blue of the lavender next to it.
Most of the plants I have chosen here will do well as long as they get at least 6 hours of sun. If you can manage that, an excellent mid-border choice for your second imaginary container could be three Salvia 'May Night' which is a nice deep blue similar to that of the lavender, and with a flower shape that also echoes the lavender. And at the back of the border you could select the Giant Shirley Foxglove mix which will introduce some shapes of purplish pinks and true pinks to your pastel garden.
Now move to imaginary container number three. Echo the pinks introduced by the foxgloves by planting three Geranium 'Sue Crug' , which have foliage that is somewhat bolder than your other front of the border plants, and flowers of soft pink with dark eyes. For mid-border, use Perovskia 'Little Spire' which closely resembles the lavender in that it has blue spikes of flowers and fine, silvery foliage. To introduce the element of repetition to the overall design, once use white Leucanthemum 'Becky' at the back of the border, just as you did when you began.
If you prefer drama, or hot colors, you will want to select bold colored plants, some with deep toned leaves. The trick here is remembering to repeat one color from the preceding “container” to give the overall garden design some unity.
So to begin a sunny bright garden, you may want to select some tall 'Golden Splendor' Trumpet lilies for the back of the border. Lilies have fine foliage but tend to be “thin” plants until they have matured to form a good-sized clump, so you will want at least six. In front of them use the bold purple foliage and golden flowers of Ligularia dentata 'Britt Marie'. The deep foliage will contrast well with the bright colors of its golden flowers – and those of the surrounding plants. At the front of the border use a few clumps of the ever-booming golden daylily 'Stella d'Oro' with its spike-shaped foliage for contrast.
Moving on to the next area, for height consider 6 Black Fritillaria. The deep spire-like flowers are near-black and so are a neutral color that will allow you to change from your yellow and orange scheme to almost anything else you desire. For drama, plant the brilliant Oriental poppy 'Turkenlouis' with its boldly fringed brilliant red flowers and deep clack center. The foliage is fairly bold and a silvery, fuzzy green. Cool things down at the front of the border with the true blue Geranium 'Brookside' which has medium foliage with just a hint of purple-black veining. There is nothing like blue to show off the brilliance of gold and yellow flowers or the brightness of a true red.
For the third area, use a single plant of Zebra grass – a tall, upright grass that is spattered with horizontal golden stripes that look like sunlight splashing off the blade-like leaves. In front, plant 3-6 of the deep blue German iris 'Persian Berry' - and for the sake of repetition and harmony, use daylily 'Stella d'Oro' at the front of the border.
In this way you are building your border one area at a time, while at the same time making sure each segment coordinates with the one next to it in color, form and texture.
Creating a great looking garden isn't hard of you use the rules of three. It takes care of your design problems, making them no more difficult than planting several large container plantings. The only key thing to remember is that a healthy plant is a happy one – and as long as your plants are good and healthy your garden will be beautiful. So make sure you pay attention to cultural conditions, planting shade plants in shade, and sun-lovers where they will get plenty of rays.
And then you will have a lovely garden.
