University of Vermont
Department of Plant and Soil Science

Spring News Article


Dr. Leonard Perry, Horticulture Professor
University of Vermont

Combining several types of flowers in the same growing container has been popular in England and Europe for some time, and has become quite popular now in this country as well.  Combine the right plants and they are easy to maintain, attractive, and perfect for those with small spaces or little time to garden. 
With so many new plants to choose from, including perennials and even tropical plants in addition to annual flowers, how do you decide?  Chris Schlegel, head grower for D.S. Cole Growers in New Hampshire, has some suggestions.  She says you should consider both cultural needs for your choices, and basic design principles.
Since your choices will be in the same container, make sure they have a similar tolerance for sun or shade.  Make sure the moisture and fertility requirements are compatible.  Use plants with similar vigor, so that one strong selection doesn’t overtake the planter and grow over less vigorous ones.  Reading the labels on plants, and asking professionals at complete garden stores, can help answer these questions. 
Then consider design.  For container gardens to have the most impact, three various plant forms should be used.  There should be tall plants that give an upright character to the planter, mounded plants to add volume, and cascading or trailing plants to visually soften the edges.  A simple combination might be the dark-leaved ‘Rubrum’ fountain grass (Pennisetum) for upright, a coleus for the volume such as ‘Alabama Sunset’, and a yellow or pink trailing petunia (Calibrachoa) to match the coleus, but provide a cascade over the side. 
You often see these referred to as “thrillers” for the upright or unusual that attract attention first, “fillers” that add the mass and fill in, and the “spillers” that cascade over the side.  Thrillers are big and bold, often with large leaves, such as an ornamental banana, black-leaved elephant ear or taro, or canna.  Thrillers can be plants with unusual foliage, vibrant colors, or unique form.  The purple-leaved millet ‘Purple Majesty’, an All-America Selections winner and annual grown from seed, provides a good example.  It would stand out, due to its size and dark leaves, among a lower combination of silver licorice plant (Helichrysum), blue fan flower (Scaevola), and verbena (most any color).   
Fillers are often foliage, filling in or weaving about the thriller.  Persian Shield (Strobilanthes), silver mint-leaf (Plectranthus), coleus, dusty miller, lantanas, and summer snapdragon (Angelonia) are examples of fillers. 
Spillers help soften pot edges and sides, and visually anchor the pot to the ground.  Often they contrast in color or texture with the other plants.   Ornamental sweet potatoes (Ipomoea) or nasturtiums are large, coarse-textured spillers for large pots.  Bacopa (Sutera) and the ‘Silver Falls’ (Dichondra) are ones for small containers for their flowers, and leaves, respectively.
You should use a variety of plant textures to add interest.  Texture is the visual effect created, usually by size or shapes of leaves.  Large foliage such as of the silver mint-leaf creates a coarse texture in comparison to the much smaller leaves and blue flowers of blue anise sage (Salvia guaranitica).  Similarly, the small leaves and red or pink flowers on airy stems of Whirling Butterflies (Gaura) contrast nicely with the larger and coarser texture dark foliage of Blackie sweet potato.
Mixed planters can be either symmetrical and formal, or asymmetrical and informal.  To be symmetrical, visually divide the container in half, and either side should be the same as the other.  To create symmetry, use even numbers of plants, and ones that remain discreet and don’t grow together. I made such a combination last year in a whiskey barrel half.  I used four red zinnias alternating with four red plumed cockscomb (Celosia), a dark-leaved millet in the center for height, red-leaved ruby leaf (Alternanthera) for a fine texture and filler, and red verbena cascading down the side.
To be most aesthetically pleasing, the plant size should be one to two times the height of the container.  So in a one-foot high container you might use a Marguerite daisy (Argyranthemum) that is under two feet high.  Use one with yellow flowers to go with the lower yellowish licorice plant ‘Lemon Twist’, chartreuse ‘Marguerite’ sweet potato vine, and to contrast with flowers of a purple trailing petunia or summer snapdragon.
Generally there are four color schemes you might consider.  Monochromatic color schemes rely on various shades of a single color, such as the yellow or red combinations described above.  Polychromatic combinations are just the opposite, using a variety of colors.  The British are famous for such combinations, often using 10 or more different flowers and colors in the same planter.
Analogous schemes use combinations of colors that are adjacent to each other on the color wheel, such as red and orange or blue and purple.  Keep in mind that warm colors (red, orange, yellow) catch your attention and are seen from a distance, while the cool colors (green, blue, purple) are more soothing and should be seen at closer range. A peach-colored trailing petunia or twinspur (Diascia) next to a coleus with red or orange foliage, such as ‘Tilt a Whirl’, would be an analogous combination.
Complimentary color schemes make use of colors that are opposite each other on the color wheel. A blue-flowered wishbone flower (Torenia) as a filler, and the yellow-leaved ‘Aurea’ creeping loosestrife (Lysimachia nummularia) as a spiller create this effect.
One last color effect is to contrast, or “echo”, one color in a leaf for instance with another plant.  So the purple from the leaves of ‘Purple Heart’ (Setcreasea) is echoed by the perfect purple match in the otherwise chartreuse leaves of the coleus ‘Gay’s Delight’.  The purple in Persian Shield echoes purple flowers of a trailing petunia around it. The pink in the ‘Tricolor’ sweet potato is used to echo pink flowers around it, as from a verbena, summer snapdragon, or twinspur.
Persian Shield, the mint-leaf, and the silver licorice plant are examples of silver foliage being used to act as a neutral color, and to bring out other colors in combinations.  White flowers also can be used effectively to separate colors that might otherwise clash.  An effective combination using white, and in fact most of these design principles, is a white Marguerite daisy, Blackie sweet potato vine, gold creeping zinnia (Sanvitalia), and blue wishbone flower. 
Don’t forget to consider herbs and vegetables in your combinations, either with flowers or by themselves.  A colorful stake with tomatoes or beans in the center of a large pot might be surrounded with carrots as filler, and flowers as spillers.  Or just surround them with beans to fill and spill.  Consider colorful Swiss chard, or red-leaved lettuces, mixed in with flowers.  There are quite a few ornamental and colorful peppers that blend well in container combinations.
Wherever you go, watch for good design combinations and make note of them and the plants.  You may want to hold plants next to each other when shopping in spring to gauge the effect.  Don’t be afraid to just start combining plants.  You’ll soon learn which you like and which work together better. The possibilities are almost infinite!

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