Thriller, Filler, Spiller: How to Design a Mixed Container

One generous pot planted with three kinds of plants can look as finished as a whole flower bed. The usual way to get there is a simple recipe called thriller, filler, spiller: something tall, something that mounds, and something that trails.

The recipe is easy to remember and forgiving to follow. What takes a little more thought is choosing plants that will be content living together, and giving them a container with enough room. Both come before any decisions about color.

What thriller, filler and spiller mean

• Thriller. The tall focal plant that gives the pot height and catches the eye first. Upright grasses, spiky foliage plants, tall salvia and upright coleus are common choices.
• Filler. Rounded, mounding plants that surround the thriller, hide its bare lower stems and make the pot look full. Geraniums, marigolds, begonias and impatiens are typical.
• Spiller. Trailing plants set at the rim to tumble over the edge and soften the line of the pot. Calibrachoa, trailing verbena, sweet potato vine and lobelia all do this.

One thriller, three to five fillers and two or three spillers is a common starting pattern for a large round pot, but it is a guide, not a formula.

Compatibility comes before style

Every plant in a mixed container shares the same light, the same potting mix and the same watering. So every plant in it must want the same light and similar moisture. A sun-loving geranium beside a shade-loving impatiens means one of them will always be unhappy, wherever you put the pot.

Read each plant tag before you buy and check three things:

• Light: all full sun, or all part shade or shade.
• Moisture: all happy with evenly moist mix, or all preferring to dry a little between waterings.
• Mature size: nothing so vigorous that it will smother its neighbors by midsummer.

For sunny spots, the list of reliable flowers for pots in full sun notes the habit of each plant, which makes it easy to pick one for each role.

Choose a container with room

A mixed pot needs width. A container about 14 to 16 in (35 to 40 cm) across is a commonly suggested starting point for a small trio, and a larger one gives you space for more fillers and spillers. Smaller pots usually look and grow better with a single kind of plant. Whatever you choose must have drainage holes.

A bigger volume of mix also holds more water, which matters when several plants are drinking from it. The guide to working out what size pot you need explains how to scale up for a group.

Where each plant goes

Placement depends on where the pot will be seen from.

• Seen from all sides: put the thriller in the center, ring it with fillers and space the spillers around the rim.
• Against a wall or in a corner: put the thriller at the back, fillers in front of it and spillers along the front and sides.

Three simple color approaches

• One color in several shades. Pale pink, mid pink and deep rose, for example. Calm and cohesive.
• Two contrasting colors. Purple with yellow, or blue with orange. Lively, and best when one color clearly dominates.
• Foliage only. Leaves in lime, burgundy, silver and green. No deadheading, and the pot looks the same from planting day to frost.

Whichever you choose, repeating a color between the filler and the spiller ties the planting together.

How to plant a mixed container, step by step

Plant tender annuals once the danger of frost has passed in your area. Have everything on hand before you begin.

1. Dampen the potting mix. Tip it into a tub, add water a little at a time and stir until it is evenly moist but not dripping.
2. Fill the container. Add mix to a few inches below the rim and firm it lightly with your hands.
3. Arrange the plants in their nursery pots. Stand them on the mix where you think they should go, step back and look from the direction the pot will be viewed. Rearrange until it looks balanced.
4. Plant the thriller first. Slide it from its pot, gently loosen any circling roots and set it so the top of the root ball sits at the same depth it grew at before.
5. Add fillers, then spillers. Work outward. Tilt the spillers slightly toward the rim so they trail the right way.
6. Fill the gaps. Tuck mix between the root balls and firm gently so there are no hollows. Leave a gap of about 1 in (2.5 cm) or more between the surface and the rim, so water can pool and soak in.
7. Water in. Water slowly at the surface until it runs from the drainage holes, then top up any spots where the mix has settled.

Two combinations to try

These are ideas, not rules. Swap in whatever your garden center has, as long as the light and moisture needs match.

• For full sun: an upright ornamental grass or tall salvia as the thriller, geraniums or compact marigolds as fillers, and calibrachoa or trailing verbena as spillers.
• For shade or part shade: an upright coleus as the thriller, begonias or impatiens as fillers, and a trailing vine such as sweet potato vine, which wants part shade more than deep shade, as the spiller.

The same recipe works in other containers. In a window box the thrillers run along the back; in a basket the spillers do most of the work, as the guide to planting a hanging basket shows.

After planting

A pot shared by several plants dries faster as they grow, and conditions vary from pot to pot with size, sun, wind and weather. Check by feeling the mix a couple of inches down, and water thoroughly when it is dry at that depth.

If one plant starts to swamp the others, trim it back.