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Perennials in Containers

Grow plants anywhere!

By Elise Ford

Penn State Master Gardener
2013

Master Gardeners Tips
  
Container plantings have long been a staple of ornamental gardening. Traditionally, containers have overflowed with annuals, but in recent years, tropical plants and perennials have become more common. An all-perennial container is a great way to showcase plants, and it's economical, as well. Plant a container once with perennials and, with a bit of maintenance, enjoy it for years to come.
 

If your space precludes traditional garden beds, you can still enjoy live plants by adding containers to front porches, courtyards, patios, decks and balconies, even rooftops. Containers also can be placed within established garden beds as focal points or to give visual interest. Consider an ornamental grass in a tall container in a sunny garden, adding a sculptural quality to that space.

  
Or imagine the impact in the shade garden of a turquoise ceramic container planted with chartreuse coral bells (Heuchera) and 'All Gold' Japanese forest grass (Hakonechloa macra).

  
The palette of perennial plants that thrive in shade is large and diverse, while the options for annuals can be limiting. Monkshood (Aconitum), anemone, Solomon's seal (Polygonatum), hosta, astilbe and bleeding heart (Dicentra) are great alternatives to impatiens and begonias. The textural contrast of a lacy astilbe paired with a solid hosta leaf is visually interesting, and for a brief period you'll get flowers, too.

Bleeding Heart flower
Bleeding Heart

A single container may best suit a space, or create a vignette using multiple containers compatible in size, style and planting. Choose a container that matches the style of your home and landscape, whether formal, modern, cottage or bungalow.

Terra cotta pots are relatively inexpensive and complement most garden styles, but their clay walls are porous and will crack from repeated freezing and thawing during winter. Glazed ceramic pots are colorful, offer a broad range of design options, but they can be expensive and susceptible to cracking if left outside for winter.

Container shrubs in a deck garden

Cast stone containers are heavy and expensive but, once planted, can be over-wintered outside if a water sealant for concrete is applied to their surface. Plastic containers are light, strong, retain moisture and are one of the least costly options.

Metal containers, such as cast iron and copper, can be over-wintered outside but get very hot in summer sun. Fiberglass pots are lightweight and come in a variety of styles to simulate stone, wood and metal. Some may be frost-proof but unable to withstand winter temperatures.

Hostas
Hostas

Avoid windy sites where containers could topple and plant foliage could be damaged. If your only option is a windswept roof, choose heavy pots and avoid plants with leaves having large surface area easily tattered in the wind. Be aware that pots in windy sites will require increased watering versus those in a wind-free spot. If the container is to be situated in baking hot sun, avoid dark colored or metal containers that act as solar collectors and can fry delicate plant roots.

Drainage is critical; plant roots in standing water will rot. If a container does not have a drainage hole, drill one and cover it with a piece of screening or landscape fabric to prevent soil from washing out. A container without a drainage hole may be used if the plants are "double potted" with a liner or plastic nursery pot. The liner is placed inside the decorative container and removed for watering and over-wintering. A container should be large enough for perennial roots to establish and, if over-wintered outside, should hold sufficient soil that plant roots do not freeze. Large pots do not need to be watered as often but are hard to move unless on casters. Smaller pots are more portable but dry out sooner.

Container soils must drain freely. Use a high-quality soil-less mix composed of sphagnum peat moss, aged bark or coir, perlite and composted manure. Coarse builder's sand or chicken grit may be added if additional drainage is needed. Invert an empty plastic pot in the bottom of a large container before adding soil to reduce the weight and amount of soil within the pot. Add a slow-release fertilizer and work evenly into the soil. Plants grown in containers require additional fertilization as their roots fill a pot and organic matter is depleted during the growing season. Use a water-soluble fertilizer at half strength with every watering or at full strength every two weeks. Stop fertilizing about six weeks before the first frost date to discourage new growth.

Astilbe
Astilbe

Before planting, determine whether the container will be viewed from one or several sides and place your plants accordingly. Choose plants that have similar cultural needs and are in scale with the size of the container. Foliage color and texture is important as perennials do not bloom continuously.

A well-designed container should look good even when not in bloom. The "thriller-filler-spiller" concept is a good template for creating effective containers. A "thriller" is a tall architectural plant placed in the center or to the back of the container. Smaller "filler" plants add mass. "Spillers" are planted last and cascade over the sides of the pot.

Water consistently, preferably in the morning. Do not allow the soil to dry completely. Plunge your finger an inch or two into the soil. If it is not cool and moist, water deeply using a gentle stream and aiming the hose at soil level. Allowing water to run out of the drainage hole encourages deeper root growth and leaches soluble salts that can damage plants.

Shrubs in Containers

Container perennials can be transplanted into established garden beds in fall or over-wintered in their containers. Cut plant foliage back and water well before the ground freezes. Move containers that cannot withstand freezing winter temperatures into an unheated garage. Water plants once a month while they are dormant. Containers over-wintered outside should be grouped together on the ground in a sheltered site, preferably on the east side of the house. Cover with leaves or evergreen boughs.

Be creative! Perennials have a diversity of foliage, habit and flowers unmatched in the plant world. Exciting container choices are now available at every price point. As a bonus you can enjoy your plants beyond a single season, whether planted out in your garden or gracing your containers for a number of years.

 

   

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