Quick Facts...
- An advantage of container gardening is its portability and suitability
for many lifestyles.
- Container gardens allow creative expression in small spaces.
- Container gardens are excellent for beginner’s as well as advanced
gardeners.
- Consider container gardens for vegetables, herbs, and concentrations
of flower color and fragrance in small spaces.
- The disadvantages of container gardens are their need for frequent
watering and fertilization.
Container gardens are one of the fastest growing segments of gardening.
Containers can be grown where traditional gardens are not possible including
apartment balconies, small courtyards, decks, patios, and areas with poor
soil. They are an ideal solution for people in rental situations, with
limited mobility, or with limited time to care for a large landscape.
Since containers are portable, they can be placed in well-used living
areas during their prime and then removed or replaced after they’ve
become spent. Container gardens add an instant landscaped look and add
color. Containers are generally comprised of annual blooming plants, and
the look is easily changed from year to year as compared to traditional
landscapes. There are a variety of plants available for containers which
are more affordable than ever before.
Container gardening is a perfect activity for beginning gardeners intimidated
by large landscape projects. Container gardens are also a great solution
for advanced gardeners who are interested in showcasing particular plants
or gardening skills.
Choosing a Container
Just about any container can be used including clay (often called terra
cotta), plastic pots, wood barrels, wire baskets lined with sphagnum moss
or coconut coir, planter boxes, ceramic pots (often found in bold colors),
and even cement blocks. However, make sure you never use a container that
held toxic materials, especially if edible plants are going to be grown.
Drainage
No matter what container you select the most important thing to consider
is drainage. Plants will not grow successfully in soil that is continually
water logged. In water logged soils, space fills with water leaving no
room for air which is necessary for proper root growth. If there are no
existing drainage holes in the container make multiple holes in the bottom.
Keep in mind that containers made from porous materials (like clay and
wood) lose moisture quickly, but allow air movement into the root zone.
However, metal, plastic, and glazed containers are non-porous – they
hold water longer, but restrict air movement making drainage holes especially
important. Use a container insert if you plan to use an expensive decorative
container without drainage holes. Make sure the insert does not rest in
water.
Weight and Size
Consider whether your pots will be moved during the growing season. When
water is added to soil in an already heavy container, the weight may be
too much to lift easily. Plan ahead when planting large containers and
add container dollies with wheels. Keep in mind tall plants require a
heavier container to avoid tipping over from imbalance or offering too
much wind resistance.
The container should be large enough so the plants won’t dry out
between waterings. Many vegetables, herbs, and flowers will not be productive
if they are allowed to wilt. Containers of minimum size hold less moisture
especially when the roots are crowded. They will need more daily maintenance
during the heat of summer. Consider using a slightly larger container
with more soil to hold moisture and reduce maintenance.
Durability and Cost
Pots that are porous may look more natural but can deteriorate quickly
if consistently exposed to moisture and freezing temperatures. Porous
containers should be brought inside to prevent cracking during the winter
months.
Non-porous containers, including glazed pottery, have a longer life span
but are often more expensive. They may be stored outdoors in the winter.
Use non-porous containers, except glazed pottery, for growing early season
plants like lettuce or pansies. They can withstand the likelihood of frost
or freezing during early spring.
The size of the container should accommodate the roots of the plants
when fully grown. Plant vegetables such as tomatoes, eggplant, pepper,
cucumbers, cabbage, and beans in a minimum of five-gallon containers.
Beets, carrots, lettuce, and green onions can be planted in three-gallon
containers. Most herbs and radishes grow well in containers of one gallon
or less. With flowers, a general rule is the larger the height of the
flower, the more root mass is produced thus requiring a larger container.
Soil
Soil Mixes
Potting soil should be free of disease organisms, insects, and weed seeds.
It should be porous yet hold water and nutrients with a slightly acidic
pH. Do not use native soil, even if you can pasteurize it. Most native
soils have a high percentage of clay particles that easily compact reducing
the oxygen that is available to the roots. Potting soil may contain pasteurized
soil, sphagnum peat moss, vermiculite, perlite, and composted manure.
Never reuse the same potting soil from the previous growing season because
it may contain disease organisms.
Soilless Mixes
Soilless mixes contain many of the same ingredients as potting soil,
but are two to three times lighter because they don’t contain heavy
soil. Common ingredients include peat moss and/or ground bark to hold
water and nutrients; vermiculite for water retention; and perlite to loosen
the mix and allow for air movement. You can add up to 10 percent of the
volume with clean, coarse sand to add weight for top-heavy plants.
Cultural Practices
Watering
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Many Coleus leaf forms and colors add interest
and unite the multiple containers in this planting. (Photo by
C. Wilson.)
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Container gardens require more frequent watering than “in-ground”
landscapes because the exposed sides of the containers result in more
evaporation. Plastic containers do not dry out as quickly as ceramic,
especially unglazed ceramic pots. Even plastic containers may require
daily or twice daily watering as plants grow larger. Do not allow containers
to dry completely or fine roots will die. Also, if allowed to dry excessively,
the potting media will shrink away from the side of the container and
be harder to re-wet.
The use of water-holding polymers or gels, mixed with the soil before
planting, can increase the amount of water held and may extend the time
between watering. There are also new self-watering pot systems that may
potentially reduce watering maintenance.
Most municipal water systems on the Front Range are from mountain sources
which are excellent and cause few problems. However, water from wells
and much of the Western Slope is often high in salts or carbonates which
will cause some problems. One way to prevent excessive salt buildup is
to water completely where 10 percent of what is added drains out the bottom.
Salt build-up is damaging to plants causing burned leaf edges, stunted
growth, and fewer blooms. If saucers are used to catch drained water,
empty them to prevent salt buildup. This can be done easily with a kitchen
baster; however, dedicate one to the garden and don’t reuse it in
the kitchen.
Water is often used to carry soluble fertilizers to the roots of container
plants. Fertilizers are forms of salts, so salt management is important
because of the need to fertilize container plants regularly.
Fertilizing
The rapid growth of many container plants quickly depletes the fertilizer
available in the limited volume of soil. Well-drained soil mixes also
result in the regular loss of fertilizer in the drainage water.
To provide the right amount of fertilizer, mix controlled-release fertilizer
granules into the soil mix at planting. The large number of plants often
grown in containers places extra demands on the fertilizer supplied by
timed-release products. Under Colorado conditions, the fertilizer supplied
by these products is generally insufficient to carry container plants
through the growing season. Use fully soluble fertilizer products added
to the irrigation water to supplement or replace timed-release products.
Organic fertilizers such as fish emulsion or blood meal can also be used
if desired, but may be available too slowly for actively growing plants,
or may develop sour aromas.
Dilute soluble fertilizers may be used with every watering, or at full
strength on a weekly or every two-week basis, depending on the type of
plants being grown. Follow product directions for concentrations and timing.
Light
It is critical to supply the right amount of light based on the plant’s
need. Follow the individualized requirements found on plant labels or
in references, and don’t mix plants with different light needs.
Consider the light available in the location where containers are to
be placed when initially selecting plants. Note that the portability of
containers allows for moving them to different locations if plant growth
falters because of too much, or too little, available light. Shifting
container locations is also desirable as the amount of available sunlight
changes with the seasons.
Reflected sunlight can be damaging to plants as well. Western exposures
may provide a risk for sun scald on many plants and this may be increased
with reflected light off lightly colored buildings and paving.
As a general guide, flowering plants, water plants, and fruiting vegetables
require a minimum of eight hours of full sun each day to perform well.
Root vegetables do best with six hours, and leafy vegetables and many
herbs should receive at least four hours of sun. Some foliage plants are
best located in filtered light or continuous shade.
Design Basics
There are a few design principles to consider when planting container
gardens. They concern dimension, shape, and color.
To avoid a flat look, add a spike, a tall plant, or a garden ornament
for height and a trailing plant to drape down from the container. A grouping
of different sized containers will also help achieve this goal. Chose
plants that are in scale with the size of your container and planting
backdrop. As a guideline, plants should be twice as tall as the visible
part of the container. If planting one large plant such as an ornamental
grass, select a larger container that will fulfill both plant growth and
design needs. Large plants can overwhelm small situations and small plants
make little impact in large spaces. Also consider whether the container
will be viewed from one side or several angles and position plants accordingly.
Consider the texture or shapes of plant leaves and flowers. A variety
of leaf shapes and sizes can be more appealing than uniform foliage. Combine
round-shaped flowers with irregularly shaped ones.
Color Wheel
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Figure 1. While combining flower colors
is a personal choice, there are design principles to keep in mind.
Use complementary colors on the opposite side of the color wheel
or analogous colors adjacent on the color wheel. Examples of complementary
colors are orange and blue or yellow and violet. Analogous color
examples are orange and yellow, or blue and violet.
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Also consider whether you want an area to stand out through the use of
hot colors like orange and red, or recede through the use of cool colors
like blue and violet. One-color compositions can be used but may look
flat. Repeating a flower color among the different vertical plant layers
will give a stronger and more unified appearance.
A grouping of containers devoted to different colors can help achieve
the composition desired. Consider the color of plants within a container
and the color among the group of containers. The colors of the containers
themselves will contribute to the entire effect.
Take advantage of the variety of foliage colors. Foliage can be silver,
gray, red, many shades of green, including yellow-green and blue-green,
and the tawny beige found in winter dormant grasses. Variegated foliage
can be the perfect complement to complete a colorful container.
Finally, use your imagination and find what pleases you. Remember that
you can easily rearrange and replace plants within a container as well
as rearrange which containers are grouped together.
Plant Possibilities
Choose plants based on light, moisture, color, height, shape, texture,
desired theme, and more.
The group of plants most immediately thought of for container use may
be annuals. In addition to new versions of old favorites, many new choices
are available. Geraniums feature new zonal, ivy, and cascading types.
New petunia colors are available as well as improved trailing types that
require no pinching or pruning. There is also a mini-trailing petunia
family species, Calibrachoa, with quarter sized blooms. Other improvements
have been seen in Verbena, Salvia, Impatien, and Fuchsia. Among the relatively
new annuals are Angelonia, Bacopa, Ipomea, Evolvulus, Bracteantha, Pentas,
Scaevola, and Torenia.
Don’t overlook “indoor” or tropical foliage plants for
shady areas. Consider Dracaena, Schefflera, Ficus, Aspidistra, and Fatshedera.
Another group of sun-loving plants is cacti and succulents, but don’t
combine them with plants that require more moisture.
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Vertical accent provided by a red-leafed
Canna. Salvia provides irregular-shaped, red flowers and Marguerite
daisy yellow, round flowers. Yellow-leafed Coleus fills in the middle
of planting with a color in the design’s “hot” yellow-red
colors. Yellow-flowered, trailing Calibrachoa and white blooming
Bacopa stretch the composition downward.
(Photo by C. Wilson.)
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Perennials can be combined with annuals to achieve design goals. Burgundy
leaf Eupatorium ‘Chocolate’ will contribute bold foliage color
as will the red and rainbow colored leaves of Canna and Caladium varieties.
For irregular-shaped flowers, try Agastache, Gaura or the more herbaceous-type
Penstemon. Agastache adds the bonus of attractive fragrances to container
gardens. Perennials are generally treated as annuals in containers and
not overwintered.
Bulbs and bulb-like plants can also be grown in containers. Consider
Asiatic and Oriental lilies, dwarf dahlias, gladiolus, montbretia (Crocosmia),
Calla lilies, Anemones, tuberous begonias, and Siberian iris.
Ornamental grasses and grass-like plants grown in containers make bold
statements. Pennisetum, Miscanthus, Calamogrostis, Deschampsia, Panicum,
and for very large containers, Phyllostachys may be considered.
Either alone or for the tall plant featured in a mixed container, consider
woody plants. Interesting single plant specimen choices are Cytisus, Caryopteris
and the dwarf conifers like Dwarf Alberta spruce, Little Gem Norway spruce,
and Blue Shag dwarf white pine. For a Japanese garden look consider Japanese
maple or Nandina. If you’re looking for red foliage, think Newport
plum.
If you want to evoke an English cottage garden, container roses make
a good choice. The bright blooms of Osteospermum, Hibiscus, and Lantana
will create a tropical feeling.
Vines on a trellis can also be used in container gardens. Consider morning
glory, Nasturtium, scarlet runner bean, or canary creeper.
Many vegetables can be successfully grown in containers. Look for varieties
that are labeled as “bush,” “patio,” “dwarf,”
or “compact.” Often variety names imply compact such as ‘Patio’
or ‘Tiny Tim’ tomatoes, ‘Spacemaster’ cucumber, ‘Morden
Midget’ eggplant, ‘Short & Sweet’ or ‘Thumbelina’
carrots. These are prolific producers that require minimal space. Read
the label for overall plant size. Vegetables suitable for containers include
beets, beans, cabbage, carrots, cucumber, eggplant, green onions, lettuce,
collards, bok choy, spinach, kale, tomatoes, peppers, and radishes.
Among the herbs suitable for containers are thyme, oregano, parsley,
rosemary, basil, chives, cilantro, and lavender. Herbs add foliage texture
and color, plus they may be edible or contribute fragrance to the landscape.
Container Maintenance
Many new annual flowers do not require deadheading to bloom over a long
period. Some removal of spent flowers is desirable with many perennial
flowers to prolong bloom. Regular harvest of herb leaves and vegetable
fruits will also prolong the useful life of these plants.
Stake or cage larger vegetable plants such as tomatoes and flowers such
as sunflowers. Vining plants such as cucumbers and morning glories will
require support from a trellis or cage.
It is difficult to overwinter plants outside in a container. The roots
will desiccate without moisture thus winter watering and protection are
necessary. Protection for containers containing woody or herbaceous perennial
species may include heavy mulching or burying the container in the ground.
Many containers, especially porous ones, will crack if the moist media
is allowed to freeze and thaw throughout the winter.
Often perennials, ornamental grasses, and woody plants are treated as
annuals in containers and not overwintered. However plants may be transplanted
into gardens and landscapes.
All media and plants should be discarded into the compost pile at the
end of the growing season. Disinfect containers by scrubbing with a 10
percent solution of chlorine bleach to kill any organisms that remain
on the container.
Water Plants
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A grouping of containers of different heights
includes a rectangular container water garden on the right.
(Photo by C. Wilson.)
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In addition to plants that grow in soil, consider aquatic plants for
container gardens. Container water gardens use water instead of soil mixes
to support plant life. Some plants float such as water lettuce, Pistia
stratiotes and water hyacinth, Eichhornia crassipes. The plants
that grow at the water’s edge, “marginals,” are potted
in a heavy clay soil in mesh pots. The pots are supported on a pedestal
of rocks or bricks to position the top of the soil at the water line within
the container.
Though containers can be small and hold one plant, a medium-sized container
allows for growing a number of plants. With a container 12 to 24 inches
wide and 12 to 16 inches deep, use the same design rules employed in combining
land plants. Select a spiky, erect, plant such as sweet-flag, Acorus
calamus, or yellow flag iris, Iris pseudacorus. Combine with
a broad-leaf plant such as giant arrowhead, Sagittaria latifolia,
or calla lily, Zantedeschia aethiopica. Add a cascading plant such
as water mint, Mentha aquatica, or parrot feather, Myriophyllum
aquaticum. Finish the planting with floating plants such as those
mentioned earlier. Two to three potted plants and some floating ones make
quite an impact.
Place the container where it will receive six hours of sun each day.
Add water every few days as it evaporates. When plants begin to grow,
add a fertilizer tablet available at the garden center where the plants
were purchased. If algae or mosquito larvae develop, remove the water
plants, empty the container, refill with clean water, and replace the
plants.
Container water gardens may either be treated as annuals or brought indoors
for the winter if a sunny location is available. Plants will require the
same six hours of sun that they do outdoors. As with annuals brought in
for the winter, be mindful of bringing spider mites and insect pests indoors
with your water plants. Examine and treat plants for pests before moving.
Indoors, a small, submersible aquarium or indoor fountain pump is useful
for aerating the water to keep it fresh. Add water as needed through the
winter. In spring, divide the plants that have grown too large and replant
the container outdoors for the summer.
An increasing number of water plant choices are available at major garden
centers. Container water gardens are actually quite simple and worth trying.
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