Patio Plants: Container Gardening With Perennials

By David Salman, High Country Gardens Founder

Container gardening has traditionally been focused on the use of annual plants, but containers are a great way to garden, and we can also use them to grow beautiful perennials and ornamental grasses. Below, Chief Horticulturist David Salman will review tips for proper planting, expanding your plant palette, and recommended container plants. 

Read on for helpful tips for success with container gardening.

• 5 Tips For Container Gardening
• How Growing In Containers Expands Your Plant Palette
• How To Protect Pots Over The Winter
• Re-Potting Perennials
• Arranging Plants: Thrillers, Fillers & Spillers
• Planting Natural Nectar For Hummingbirds

1. Use bigger pots. (Note: I use the words container and pot interchangeably.) Avoid using pots that are too small. Plants quickly become root-bound and it becomes difficult if not impossible to keep them adequately watered and fertilized. I always use at least a 14-inch diameter pot. Remember: The bigger the mature plant, the bigger the pot.
2. Always use a soil-less potting mix. Filling pots with garden soil is a recipe for failure. Garden soil compacts and greatly restricts drainage and air exchange. I always recommend a high quality soil-less potting mix. This potting mix can be reused each season and enhanced with new ingredients.
3. Keep the plants well fertilized. Because we must water pots more frequently than plants in the ground, we need to replenish nutrients that are flushed away. If you want to grow your pots organically, top-dress every couple of weeks with earthworm compost and Yum Yum Mix. Compost tea is also excellent. Growing conventionally, use Osmocote slow release fertilizer mixed into the soil at potting time and supplement with water-soluble Miracle-Gro (or equivalent) once every week or two.
4. Don't put gravel in the bottom of the pot! Counter to popular belief, adding gravel to the bottom of the pot actually encourages water to saturate soil, and makes it more difficult for the water to leave the soil. This is a useless technique that can actually restrict drainage in the pots. Fill the pots completely with soil-less mix. Be sure that there are drainage holes in the bottom of your pot. If the pot has a large drainage hole, I'll put an irregular rock over the hole that doesn't seal the hole and allows for water to flow out.
5. Leaving pots out-of-doors year-round: If you want to leave your containers outside year-round, I recommend using a fiberglass pot or the pot-in-pot strategy to avoid cracked pots and cold damaged roots. For pot-in-pot cultivation, plant in a plastic nursery container and drop this pot into a slightly larger ceramic pot. Fill the empty space in between with small bark nuggets. This insulates the inside pot from heat and cold and allows winter watering without cracking the ceramic pot.

Perennials that may seem impossible to grow in the ground become easily cultivated in pots.

For instance, gardeners living east of the Mississippi will find the use of containers as a great way to expand their palette of perennials. This is especially true when it comes to growing xeric plants that would be unhappy in the ground because of excessive moisture and soggy freeze-thaw conditions in spring. I can't recount how many gardeners have asked me how to grow Agastache (Hummingbird Mint) in cold, moist, midwestern or eastern climates. The answer: plant them in pots. The same goes for growing Lavender, native Sage (Salvia greggii and hybrids), and other popular xeric plants!

Conversely, Western and dry-area gardeners may use containers to grow selected plants that require richer soil and more frequent watering. 

Containers are also a great way to grow perennials that aren't quite winter-hardy enough for in-ground cultivation in your region. For example, gardeners in Zones 4 and 5, fcan enjoy Perennial African Daisy (Gazania), native Sage cultivars/hybrids (Salvia greggii), and Spanish Lavender (Lavandula stoechas) by planting in containers and overwintering the plants indoors. 

We need to protect the pots and their resident perennial plants from the extremes of the winter weather.

• After several hard frosts, move them into an unheated garage or cold frame.
• If this isn't practical or you have a lot of pots to protect, make a straw bale enclosure where the pots can be placed. Cover with a couple of sturdy pieces of row crop cover (frost blanket) fabric.
• Be sure to give the pots a drink every month or so on a warm day so the roots don't dry out excessively.
• In spring, cut the perennials back and move them into the outside position.

When using perennial plants, they can remain in the pot for at least two seasons before re-potting them into a larger one. Or the perennials can be divided and re-planted back into the same pot with fresh soil-less mix.

When designing your container garden, make sure pots have a mix of plants: thrillers, fillers and spillers. Perennial plants that appreciate well-drained soil are a great choice for containers.

Remember the container gardening mantra, "thrillers, fillers, and spillers." 

• Thrillers: The tallest, showiest plants go in the middle of the pot. Consider upright Agastache, Salvia, Penstemon, and Ornamental Grasses
• Fillers: The medium-sized plants go around the center plant. Consider Stachys, Coreopsis, Salvia, or mounding Ornamental Grasses.
• Spillers: Soften the edges of the pots by planting trailing plants. Consider Sedum, Creeping Thyme, Santolina, Aubrieta, or Zauschneria.

When planting a pot or a container against a wall, put the tallest plants on the side of the pot that's closest to the wall.

As a hummingbird gardener, I recommend planting hummingbird attracting flowers and placing them around your outdoor living areas as a replacement or supplement to hummingbird feeders. When hummingbirds discover a reliable source of nectar, they will return for years to come.

Pots filled with Hummingbird Mint (Agastache), native Sage (Salvia), Monardella, Hummingbird Trumpet (Zauschneria) and Coral Bells (Heuchera) make colorful, nectar-rich containers. Even better, these plants are showy and wonderfully fragrant, so planting them near your outdoor spaces where you can enjoy the benefits is a great addition to the garden.

Our friends at The Hummingbird Society grow Agastache, Salvia, Penstemon, Honeysuckle, and more in containers to feed hummingbirds at their Arizona headquarters.

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