Thrills & Spills

Taking container gardens to new heights.

If you research container gardening, you’ll probably find this classic technique used by beginning and professional gardeners alike: Thriller, Filler, and Spiller. The thriller is the tallest element of the arrangement and helps define the silhouette and overall vibe. Fillers are the mounding varieties positioned as the next tier down from the thriller. Spillers are the trailing, spreading plants placed along the perimeter of the container to soften the edges and cascade toward the ground.

While I don’t know the origin of this terminology, I do know it’s a universal practice that has stood the test of time. Whether you’ve tried this approach before or this is the first you’ve heard of it, get ready to take it to the next level. Try these tips to elevate your usual container gardens into lush, high-end designs this summer.

DESIGN FOR DRAMA

First, exaggerate the height of your thriller to create both balance and drama. You always want the plants to grow in proportion to the container and your space. In general, the tallest vertical element in a design should be about as tall as the planter. This means a container that is 24 inches tall needs a vertical element that will grow to at least 24 inches high. Please don’t skimp on your thrillers!

When designing for an open space without a ceiling, roof, or other overhead structure—imagine the hardscape surrounding a pool or the entrance to an office building—go even higher to create a really dramatic impact! In these scenarios, select a thriller that will grow up to twice as tall as the planter. Note, though, that taller plants often have wider root balls, so be sure your planter will accommodate it.

Another way to create a well-rounded, high-end container garden is to use what I call the “Bullseye Approach” (see the diagram on p. 121). Here, we layer plants in concentric circles of descending heights as we move away from the middle of the planter. Start with a tall, eye-catching thriller as the centerpiece of the arrangement. Then, add a set of three mounding fillers evenly spaced around the centerpiece in ring “B” to begin the transition to the outer edge of the pot. Next, position three low, spreading spillers in the openings between the fillers, but closer to the edge of the pot in ring “C” so they’ll soon cascade down the sides. This pattern surrounding the thriller creates a rhythm to the design and results in a full, layered arrangement to be enjoyed from all angles.

As you get more comfortable with this approach, start adding more plants to the arrangements by alternating flowering and foliage varieties within each circle. For example, build a pattern alternating coleus (foliage plants) and Whopper Begonias (flowering plants) in ring “B.” If you’re feeling adventurous, build a similar pattern with your spillers in ring “C,” and you’ll quickly find you’re creating an abundant mound of color and texture.

PLAN FOR SUCCESS

People often tell me how overwhelmed they feel when they shop for plants. The key is not to panic—be prepared so you know exactly what to look for.

First, note your sun exposure—the amount of sun your planter will be exposed to on a typical summer day. The standard ranges for the gardening industry are full sun, part sun/part shade, and full shade.

Full sun: Locations with six or more hours of direct sun each day. This is usually the side of your property that faces south.

Part sun/part shade: These terms are often used interchangeably and are defined as three to six hours of direct sun, preferably in the morning or early evening. Areas exposed to three to six hours of direct midday sun should be categorized as full sun.

Full shade: Less than three hours of direct sun each day. This is typically the north side of your property, where sunlight may trickle in briefly during the day.

Next, measure the height and width of your container. Just as the height of your container should dictate the height of your thriller, the diameter of your container will tell you how many individual plants you can fit around that thriller. Achieving a deluxe look requires more plants than you might think; you’d be amazed by how much plant material we put into one arrangement!

At left are some general guidelines for the three categories of plants needed to fill common sizes of round pots. You can always improvise based on what’s available and the look you want to create. Don’t be afraid to experiment by adding even more plants—or doing the opposite and using fewer plants that are already more established and fill your design immediately.

If you see a plant that intrigues or energizes you but doesn’t exactly match your sun exposure or size criteria, try it anyway. Many plants are resilient and can adapt to less-than-ideal conditions.

—Steph Green, Contained Creations

SHOPPING FOR PLANTS

Once you’ve determined your ideal thriller height, sun exposure, and approximate number of fillers and spillers, you have all of the information you need to get started. It’s time to shop for the plants you need.

Garden centers typically group their summer annuals according to the amount of sunlight they need to thrive (full sun, part sun/part shade, full shade). Take a cue from the displays and start at the tables that match the location of your planters at home. Double check by reading the plant tags showing each plant’s preferred sun exposure to ensure you select a mix of plants with similar light needs.

These tags also tell you each plant’s finished height and spread at maturity, so you can choose thrillers, fillers, and spillers that will fit well together and grow into the design you wish to create. Because room for root growth is more limited in a container than it is in the ground, plants may max out at the lower end of the range listed on their tags.

PICKING POTS

Planters are available in all styles, sizes, materials, and price points. For more traditional settings, antique lead, iron, and cast stone pieces are popular choices. For more transitional or contemporary settings, glazed ceramics and streamlined geometric silhouettes are great alternatives.

If you desire a lighter weight option, fiberglass composites have become more readily available in attractive styles. These pieces mimic heavier versions at a fraction of the weight. They can often be shipped directly to you, or be transported by car, and easily put into place on your property—no professional handling required.

If you plan to leave your planters outside during the winter months, choose a material that is labeled frost-proof, or at least frost-resistant. Also, be sure your planters have proper drainage, so excess water is able to escape via the drainage holes, especially in the cold winter months. If your planter retains water, it will be more susceptible to freeze and thaw cycles, which can lead to cracking.

Shopping virtually? Try these online sources:

  • BurkeDecor.com
  • CrescentGarden.com
  • PennoyerNewman.com
  • ShopTerrain.com
  • VeradekShop.com
  • Wayfair.com

Prefer to shop in person? Try these Virginia retailers:

  • Colesville Nursery, Ashland
  • Great Big Greenhouse & Meadows Farms Nursery, Richmond
  • Ivy Nursery, Charlottesville
  • Sneed’s Nursery, Richmond
  • Strange’s Florists, Greenhouses, & Garden Centers, Richmond
  • The Greenhouse, Glen Allen

WATERING CONTAINER GARDENS

Regular watering is key to keeping your containers lush and green, but you shouldn’t just splash it on. Follow these guidelines for the best results.

Check the soil and observe the plants before watering. In general, the soil should be kept in a state much like a wrung-out sponge—not soupy and wet, and not dry and crusty.

Water at the base of the plants. Showering the entire arrangement may seem satisfying, but dense foliage and flowers can actually block the water from reaching the roots, where the plants can absorb it. Use a rain wand or sprayer that gently disperses the water and won’t wash dirt away from the root systems. My favorite sprayer is the Dramm One Touch Shower and Stream.

Water in the early morning or early evening. That’s when temperatures are cool and roots aren’t stressed, so they will absorb more water. Avoid watering late at night; the lack of light will minimize evaporation of excess moisture and can lead to the growth of fungus.

Water deeply and slowly. Then, pause to see if excess is escaping through the drainage hole. For large planters, it may take a while for excess to work its way down, so move on to the next pot, then come back to check. If the potting mix is overly dry, it may actually repel the water at first and prematurely send it out the drainage hole, tricking you into thinking you’ve watered enough. This is why it’s so important to check the status of the dirt before you water. 

Watch for clogs. If you find the soil is staying soupy and/or you notice a rotten smell coming from your planter, you may have a clogged drainage hole. To confirm, tilt the planter and gently poke a stick or other object into the drainage hole to see if you can dislodge the clog and release excess water.

Get a lightweight hose. Container gardens require frequent deep watering. We’re all likely to be more successful if we have a good hose system in place. There are some great lightweight expandable hoses on the market, like the Xhose, that make it a breeze to move around your property to water.

My final piece of advice is to take a risk once in a while. If you see a plant that intrigues or energizes you but doesn’t exactly match your sun exposure or size criteria, try it anyway. Many plants are resilient and can adapt to less-than-ideal conditions. If you notice it struggling mid-season, you can always remove it from the arrangement and transplant it to a better suited location. This trial and error is part of the beauty and flexibility of container gardening.

I hope you experiment with something different and dramatic to elevate your container garden designs this year!

TRICKS AND TOOLS OF THE TRADE

1 Styrofoam Blocks

Use leftover Styrofoam blocks to take up space in the bottom third or half of oversized planters. Place a drainage disc over the drainage hole in the empty pot, then position several Styrofoam blocks to take up space in the cavity of the planter. Make sure they aren’t blocking the path for excess water to reach the drainage disc. Also, make sure they are low enough that the largest root balls of your new arrangement aren’t crowded and have plenty of room and potting mix beneath them.

2 Drainage Discs

To prevent clogs in drainage holes and to minimize the amount of dirt that may escape, place a Drain Smart disc in the bottom of your planters before you add potting mix.

3 Fertilizer

When you plant your summer arrangement, sprinkle an all-purpose granular fertilizer on top of the potting mix before adding the plants. This should fuel the plants for three to four months. Because container gardens require such frequent watering, nutrients are gradually washed out of the dirt and need to be replenished sooner. For a late- season boost of nutrients, you can water your containers with a water-soluble fertilizer.

4 Sphagnum Moss or Shredded Hardwood Mulch

Add a layer of sphagnum moss or shredded hardwood mulch at the base of freshly installed plants to protect the roots from extreme swings in temperature, minimize erosion, and give your arrangement a more finished look. Immerse dry sphagnum moss in water for a few minutes before applying. Simply grab a wet handful and ring it out, then tuck it in between your plants to cover any exposed dirt. Dry mulch also gets the job done.

5 Pruning Saw or Hori Hori Knife

If your pots have well-established plants from a prior season that need to be removed, try a pruning saw or hori hori knife to cut out stubborn root systems.

6 Pot Risers

These tough little rubber squares sit discretely under your planters to lift them off the hardscape, encouraging good drainage, increasing air flow, and minimizing water damage and staining. They’re also great for leveling pots on slightly uneven surfaces.

7 Garden Snips

These petite clippers are ideal for deadheading annuals or harvesting herbs. They have short, agile blades that give a nice clean cut without mashing or bruising the stems.

8 Potting Mix

Opt for potting mix over garden or planting mixes. Potting mix is an ideal growing medium for potted plants because it tends to be fluffier and reduces compacting, allowing water and air to easily reach the roots.

This article originally appeared in the June 2021 issue.

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