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.
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.
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.
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.
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.
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.