First, the pros say, evaluate your surroundings.
“Groups of big planters are useful for softening edges and corners of large spaces,” explains Todd Holloway, owner of Pot Incorporated, an award-winning container and landscaping company in Vancouver, British Columbia. “Singular, large planters can be used symmetrically at the corners of spaces to add height and boundaries that define architectural elements. Large bowls are being used more frequently as focal points or as companions to seating areas in outdoor rooms. And oversized containers can add an organic element against bare walls next to outdoor gathering places.”
When used appropriately, says Holloway, large containers can also direct traffic throughout garden paths. “Framing your garden spaces with large planters,” he notes, “is also a great way of incorporating color and interest as a trick to invite guests into the area.”
How tall should you go? A general rule of thumb, says Holloway, is to keep the tallest designs around the perimeter of a space and the lower ones around furniture and gathering spaces. When it comes to the proportions of the designs themselves, he advises using the “rule of thirds” – devote one third of the height to the pot and the remaining two-thirds to the plants, or vice versa.
Dan Benarcik, a horticulturist who designs large container gardens for Chanticleer (a famous public estate garden in the Philadelphia area), likes using big designs as doorway flankers and as anchors for the corners of patios. He also likes positioning pots so that “there’s an experience with them.” For instance, he places them so they’ll be backlit by the sun, giving colorful or variegated foliage a brilliant, stained-glass glow. One of his favorites for this use is the colorfully foliaged Tropicanna® cannas.
Don’t get too worried about making your container garden “too tall,” says Benarcik: “People have more problems with achieving height than the other way around.” In the end, he says, it comes down to learning from experience and developing your own idea of what’s aesthetically pleasing.
Next, choose at least one plant that will give you the height you need.
“When you’re going out to buy the plants to fill your containers, you really want to think in threes,” says the Massachusetts-based Dave Epstein in one of his recent Growing Wisdom how-to videos on creating containers. “You want something that spills over the sides … something that fills the center … and something that’s the ‘wow factor,’ or what some people call the ‘thriller.’”
The “thriller” is where you can bring in the height, says Epstein, choosing the colorfully foliaged Tropicanna cannas, (with white petunias as the spiller and magenta celosia as the filler).
“Tropicanna cannas are ideal for a couple of reasons,” says Epstein, also recommending taller tropical and large-leaved plants and grasses for height or volume. “First, they are very forgiving. If clients miss a watering cycle, the plants bounce back. On the other hand, they can stand wet feet to the point of being used as water garden plants.” The colorful foliage means season-long interest, he adds, although the lily-like, tropical blooms are certainly a bonus. “And since there are several leaf colors to the cannas, you can design almost any container and incorporate the canna into the middle or back of the arrangement.”
Benarcik is a fan of cannas, too: “Pound for pound, cannas are the best plants for large container gardens, and surprisingly drought tolerant,” he says. His other recommendations for big planters include cordylines, phormiums (New Zealand flax – “especially the dusty or brown tones”), bulbines (he likes ‘Hallmark’), hibiscus, brugmansia (Angel’s trumpet), chenille plant (especially ‘Inferno’), coleus, banana, alocasia, variegated cassava (tapioca) and larger bromeliads (especially the orange and burgundy tones).
In addition to cannas, bananas, alocasias and colocasias, Holloway likes using papyrus, bamboo (for a fine-textured, organic, modern feel), daturas, fuchsias and abutilon. He also loves interestingly shaped conifers, noting that large containers can be beautiful with just one plant – or as many as you feel the design calls for. “Using them in colder areas allows you to hold on to year-round interest,” he says. “Alternately, you could use deciduous trees with charming bark or branching appeal.”
Epstein, who also uses conifers, will sometimes even use just the branches to extend the height of a piece.
“And, with the rising interest in growing food,” says Holloway, “large containers can serve as an exceptional extension of your food garden to reduce just a few more food miles.” His recommendations for large-container edibles include: artichokes, twining pole beans, tomatoes, cucumbers and even squash vines. “Fruit trees and berry bushes or vines can also be used effectively in large planters,” he suggests, citing dwarf apples and pears, fig trees or raspberry plants as alternatives to ornamental plants in grandiose containers. “If you have some wall space or arbors to cover, try grape or kiwi vines in large planters.”
When it comes to mixing and matching plants, Epstein says it’s about echoing or contrasting colors and textures. In his video, he notes how the broad, flat, ovate or lanceolate leaves of Tropicanna cannas differ from the fleshy rosettes of echeveria, yet the two go together, since they’re both shades of burgundy. In that same pot, however, he notes how you can contrast the dark burgundy with either a white petunia or purplish-pink celosia. “And don’t forget the color of the pot,” he says, noting it also can coordinate or contrast with the rest of the design.
Epstein’s also a big fan of using Flower Carpet® groundcover roses and Festival™ Burgundy cordyline in large containers, for their natural pest and disease resistance, season-long interest and ability to withstand extreme climate conditions.
“If you want roses that stand up to hot, dry conditions in containers, the original Flower Carpet line is an excellent choice,” he says. “For hot, humid weather, Flower Carpet’s new Next Generation line – which got excellent reviews from the Dallas Arboretum – is your best bet.” Festival, he adds, is extremely architectural, with its graceful fountains of burgundy, glossy, straplike leaves.
Jimmy Turner, senior director of gardens at the Dallas Arboretum, loves to use the Storm™ series of agapanthus in large containers. After all, it was the only agapanthus to survive in the arboretum’s famous plant trials in intense heat, drought and humidity.
When it comes to larger containers, Epstein likes lightweight, synthetic pots mimicking the look of heavier materials that dry out quicker (like wood, metal or clay). If the pot doesn’t already have holes for drainage on the bottom, he adds them with a drill. For even better drainage, he then fills the bottom of the pot with rocks (or even sticks, shells and other organic matter) and then a soilless, lightweight potting mix.
After filling the pot about halfway with the mix and working in a slow-release, granular fertilizer, Epstein likes to pot the tallest plant first, first loosening its roots. (If you put the tall plant in the center, the filler can go all the way around that and the spiller all the way around that, he notes. If you put the tall plant in back, the filler can go in front of that and the spiller in front of that). After the plants go in, Epstein adds a layer of mulch on top of the soil to help hold in moisture.
Larger plants also demand larger containers that can accommodate the roots of the plants’ ultimate size, says Holloway, adding that a larger volume of soil can also hold more water, longer. “At the very least, your container's volume should be roughly a third to a half the size of the eventual volume of the mature plants,” he says.
If your mature plants are expected to grow to 3 feet tall by 3 feet wide, for instance, your planter should be no smaller than 1 to 1.5 feet tall by 1 to 1.5 feet wide.
Epstein recommends watering in the cool of the morning (for less evaporation). “Make it part of your morning routine, like brushing your teeth,” he suggests. “Then you don’t have to think about it the rest of the day.”
First, he says, check the moisture level by sticking your finger 2 to 3 inches into the soil. Only water if it’s dry, to prevent overwatering. In addition to the slow-release granular fertilizer, you’ll also have to feed your large containers with liquid fertilizer for optimum growth and performance.
“It’s a hard truth – plants in containers do dry out quicker than those in the ground – and larger designs, especially, do require some maintenance,” says Epstein. “But with a bit of front-end planning and a few expert tricks, you’ll have magazine-worthy containers to enjoy the whole season.”