As the name implies, thrillers are the big, attention-getting star players. They are usually tall, upright plants, with outstanding qualities—such as colorful foliage, intriguing shape, or dramatic flowers—that last all season long. Many thrillers are architectural: plants with structural, eye-catching form that can serve as a sturdy backbone or rugged framework for a scrim of less substantial plants. Think of the boldly colorful, paddlelike leaves of Canna ‘Pretoria’ or the bright spikes of Yucca filamentosa ‘Gold Edge’.

Thrillers work best in compositions where they are the tallest plant. For me, they are also the starting point in a container design. I select my thriller, then build around it. At planting time, the thriller goes in the center of a pot that will be viewed from all sides or at the back of a pot that will be displayed in a corner or against a wall.

Fillers add mass

Next, I add the fillers—billowy, more finely textured plants that surround and weave through the thriller. Fillers add mass to the overall composition and, more important, establish a dialogue with the thriller. Fillers add a textural contrast or colorful counterpoint. In a monochromatic composition, they may simply echo the thriller, though with less saturated color or at a reduced scale. Texturally, I might use a round-leaved filler with a spiky thriller. Since fillers are usually plants with a mounded silhouette, they also do just what the name implies: They fill up the pot while embracing the thriller. Often, they help by hiding the bare knees—the less interesting stems or stalks—of their larger neighbor.

When planting a pot, I position my fillers around the thriller. I often use a mix of plants for this job: some with foliar interest, others with flowers. For flowery fillers, I avoid perennial varieties in favor of uncommon, striking annuals or tender perennials for their much longer flowering season. Since the goal of container plants is to attract the eye, these plants add an alluring unusual flavor. I like bountiful-looking containers, so I cram in as many fillers as I can.

Spillers anchor the pot

I often have just enough room left to shoehorn in a few spillers toward the edge of the pot. Sometimes it’s fun to unify a composition by training a few tendrils of a spiller to climb into and through both the filler and the thriller. The main role of a spiller, however, is to sprawl over the side of the container, softening its edges and tumbling toward the ground. When parts of a container planting touch the earth, the pot looks rooted to its place.

But spillers should do more than soften a pot and link it to its place. Well-chosen spillers continue the dialogue begun by the thriller and filler. To deepen that conversation, I look for spillers that echo or contrast with the pot’s other plants by virtue of shape, color, or texture.

Each plant plays a role

The photo at right is a good example of a well-balanced container planting. Thrillers like this New Zealand flax (Phormium cookianum ‘Maori Sunrise’, USDA Hardiness Zones 9–10) are the highlight of the container and are often where ideas originate.

As a filler, salvia (Salvia splendens cv., annual) is doing what any good sidekick should do: make the hero—the thriller—look good.

A good spiller like licorice plant (Helichrysum petiolare ‘Variegatum’, Zones 10–11) can end up being a mini-thriller, just growing down instead of up.

Keep scale in mind

Planting the right combination of thrillers, fillers, and spillers creates a lush, intriguing composition rich in color, texture, and form. It fills out a pot by exploiting space in every available direction—up, down, and sideways. When selecting plants, I also consider the element of scale. Though I often aim for extreme contrasts in terms of color combination, texture, and shape, I like to use plants more closely related in size. I usually try to group plants using fillers that are roughly between one-third and two-thirds the size of the thriller.

I also bear in mind that the boundaries between my three basic plant types aren’t fixed. Depending on the arrangement and scale of a planting, some fillers might get promoted to thriller, some fillers—many kinds of verbena, for example—might spill a little, and some thrillers might serve as fillers when paired with something larger and even more exotic. But it’s not necessary to overthink the process. No matter what the specific plant, using a thriller, a filler, and a spiller is a sure recipe for success.