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Shrubs: Growing Shrubs In Containers
by Kent Gullickson
Aesthetics and restricted space are the most common reasons for growing shrubs in containers. Millions of people, especially in urban situations, do all their gardening in pots— and quite successfully, too, as the rooftops and balconies of big cities from Manhattan to Rome attest.
Whatever the reason for growing plants in pots, container gardening often results in a relationship between gardener and plant that rather resembles that between a parent and a young child. Potted plants remain dependent for water and feeding long after individuals of the same species will have gained at least a measure of self-sufficiency in the ground. Container-grown plants do not have access to the same reserves of nutrients and water that shrubs planted out have; interruption of the supply of either is stressful for plants; and like people, plants under stress often perform poorly.
Pittosporum tobira is prized for its lustrous, dark green leaves.
The yellow flower clusters of Mahonia lomarifolia mature to powdery blue berries.
Loropetalum chinense rubrum is a neat, compact shrub with tiered, cascading branches.
But growing shrubs in pots also has its advantages. Perhaps the most compelling reason to put up with the added effort of it all is simply that in pots you're able to grow things that otherwise wouldn't survive in the garden. For example, our garden is located in a "banana belt" in the foothills of Oakland, California, and is essentially frost-free most winters. Our biggest problem isn't the cold, it's the soil— heavy, thick, dark, sticky clay with a six-inch overlay of good soil in the best spots. I have a fondness for aloes, especially some of the ones that get big, and I've lost some to cold, but more to wet feet. In any case, if they're in pots, plants can be moved in out of the cold, and good drainage is simply a matter of using the right soil mix.
Growing shrubs in containers does present a few peculiar challenges, but isn't really much different from growing shrubs in the ground. Sun and shade requirements remain the same, and regular fertilizing is important to maintain good growth and leaf color. Of course, watering is the most critical aspect of maintenance. One hot afternoon in bone-dry soil can be the death of many potted plants. Containerized shrubs should be thoroughly soaked and then the soil should be allowed to become dry to the touch before more water is added.
Shrubs need repotting occasionally; either into larger pots if you want the plant to grow, or into the same pot time after time, following root and top pruning. This not only keeps the specimen from growing too large but also enables you to freshen up the soil by replacing at least a part of it. After repotting, shrubs respond with fresh, vigorous root and top growth; shrubs that are pot-bound or root-bound at first languish and ultimately decline.
Some plants tolerate container growing better than others (click here for chart). Many fast-growing plants are poor candidates for containers because they need almost constant repotting. On the other hand, relatively slow-growing plants can make excellent container subjects.
There are two things to avoid with container-grown shrubs. First, whenever repotting, avoid the often disastrous practice of removing a plant by pulling it out of the pot by the stems or trunk. Always invert the pot (if possible) to let gravity help remove the soil mass, or lay the plant on its side, and gently coax the root ball out of the pot. Second, don't use pots without drainage holes; wet feet can be murder on your shrubs. If necessary, double-pot shrubs directly in a container with drainage, and then place this pot into a larger, decorative container without holes to catch the runoff.
Kent Gullickson is a horticulturalist and garden designer in Oakland, California, specializing in perennials and pond gardens. He has managed nurseries and garden centers throughout Northern California.