The Art of the Thriller, Filler, & Spiller: A simple formula for designing beautiful container gardens every season of the year

Maika Mattson and Clare Janetzki

April 27, 2026

Container gardens are one of the most rewarding ways to bring beauty to a patio, balcony, or doorstep. But there's a difference between a pot of plants and a pot that makes people stop and stare. That difference comes down to a single, elegant design formula: the thriller, filler, and spiller.

Whether you're starting your first container or reinventing an existing one, this framework will help you create lush, layered, professional-looking plantings that perform all season long.

The Formula

You can view the container as ‘the stage,’ the thriller as ‘the drama,’ the filler as ‘the body,’ and the spiller as ‘the finish.’ The container sets the tone, the thriller is typically the most striking or tallest element, the filler provides the bulk of texture and color, and the spiller spills out of the container to create length and soften the edges.

Plant by Season - Four Seasons of Containers

The beauty of the thriller-filler-spiller formula is that it works year-round. Below are some of our favorite combinations for each time of year. Plants marked with an asterisk (*) are annuals that complete their life cycle in one growing season.

Keeping it Beautiful - Care & Maintenance

Container plants are dependent on you for everything: water, nutrients, and grooming. The good news? A consistent routine is simple, and the payoff is enormous.

Watering

Water most pots until it runs out of the drainage holes to ensure thorough saturation. During the hottest months, most containers need daily watering, occasionally skipping a day as needed. In the rainy season, covered containers still need weekly attention. For more watering tips, check out our blog on 'watering tips to survive the dry Seattle summer.’

Fertilizing

Container plants have limited resources and depend on you for nutrients. Add a slow-release organic fertilizer at planting time and reapply monthly. Supplement with a liquid fertilizer every two weeks for an extra boost during peak growth and bloom periods.

Deadheading & pruning

Remove spent blooms before they set seed; this encourages continuous flowering throughout the season. Don't be afraid to trim plants that are crowding their neighbors and cut back anything that looks stressed after heat or missed waterings to encourage fresh growth.

Getting started - How to Plant Your Container

Start with quality potting soil

Reach for a high-quality organic potting mix formulated for containers, not garden soil, which compacts and drains poorly in pots. Good soil is the foundation everything else depends on.

Water your plants before planting

Make sure all of your plants are thoroughly watered before you begin, or submerge the nursery pots in a bucket of water until the soil is fully saturated. Dry root balls can be difficult to re-wet once buried.

Arrange and plant

Fill the bottom two-thirds of your pot with potting soil, mix in a starter fertilizer, and arrange plants so the top of their soil sits about 2 inches below the container rim. Start with your thriller, work outward with fillers, and tuck spillers around the edges.

Water thoroughly

Once everything is in place, water the container deeply to settle the soil around all the roots and eliminate air pockets. This is the start of your daily water-and-care routine, and the most important moment to get it right.

Ready to build your most beautiful pot yet?

Container gardens are a wonderful, low-commitment way to experiment with plants you might not grow in your garden beds, express your style through color and texture, and bring life to spaces that feel overlooked. With the thriller-filler-spiller formula as your guide, you'll be designing beautiful pots in no time.

Sources:

The Seattle Times, ‘How to create beautiful, functional container gardens on balconies and patios’

Dennis' 7 Dees, ‘Container Garden Care & Maintenance’

MMApril 27, 2026West Seattle Nursery