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Conifers and container gardening can be a good match both visually and culturally.
Appearance-wise, a container elevates (literally and figuratively) a slow-growing dwarf specimen so that it may be better noticed and admired. These tiny trees or shrubs also lend themselves to creative container planting; accessorize the pot with stones and creeping perennials to evoke a full landscape in miniature. Evergreen conifers of larger size keep a container interesting all year and fit beautifully into outdoor winter decorating schemes.
In terms of culture, containers can be an asset to gardeners who wish to grow conifers but have less than ideal in-ground conditions. Container gardening allows you to mix a custom growing medium on a small scale and more easily provide adequate drainage and the right amount of moisture. Pots and dwarf conifers give small-space gardeners the opportunity to tend a colorful collection of trees and shrubs, as seen in the deck garden Sharon Elkan has created at her Oregon apartment.
Key steps for container gardening with conifers:
Choose a plant that is winter hardy to at least one USDA Zone warmer than the one in which you garden. For example, if you garden in Zone 6, the plant should be hardy to Zone 5 or colder. (This is true for any perennial, tree or shrub that will be left outdoors in a container year-round.)
Purchase a pot-grown conifer rather than a balled-and-burlapped one. The former will grow well continuing in a container, while the latter has spent time growing in the ground before being dug and packaged for sale, and would fare best going back into the ground.
Choose the right size container. The diameter should not be more than twice that of the plant's nursery pot if it will be a single planting, or larger if you intend to make a mixed planting. Using a pot that's too big can easily lead to root rot. Keep in mind that many conifers, especially those labeled dwarf, grow quite slowly and will likely be able to remain in the same container for years. In cold regions be sure the container is frost-proof.
Be certain the container has drainage holes, and use a potting medium that drains freely, such as a bark-based mix. Conifers require sharp drainage.
Research your chosen conifer to learn about how much water it needs. Keep in mind that containers dry out more quickly than the ground, so you may need to water more frequently. Mulch the pot to conserve moisture. Water the potted conifer right through the fall and again during any winter thaws.
If the container stands in a spot subject to winter winds, move it for the winter or set up a windbreak. Winds can dry the plant's needles.
Most conifers prefer sun. Place your container in a position to meet the plant's light requirements, however you may move the pot to a place where it will get some shade during the winter, to help prevent wide swings in soil temperature.
For added protection over the winter, especially with small pots, consider burying the pot in the ground before it freezes, or mounding mulch up around the sides of the pot. These methods will insulate the roots. If you've chosen a plant hardier than your zone, this may not be necessary, but better safe than sorry. Another option is to move the pot into a frost-free space such as a garage or cellar, or pull the container up against the wall of the house, as this space tends to be warmer than the open landscape.
To fertilize, remove the mulch and apply a layer of compost in early spring, then reapply the mulch. Alternatively, use a slow-release fertilizer annually or a very weak solution of water-soluble fertilizer weekly during the growing season (use one fifth of the recommended dose).
If you're planting other dwarf shrubs, perennials or seasonal annuals in the same container, make sure their needs and rate of growth match up to those of your conifer. When in doubt, or to widen your palette, keep each plant to its own container and group the pots together to make a vignette. For a cohesive look, use containers of the same color and material, but in different shapes and heights as appropriate for the plants.
Recommended related reading:
Gardening With Conifers by Adrian Bloom provides plant recommendations as well as design inspiration and care techniques for these treasured garden plants.
Conifers for Gardens, Richard Bitner's encyclopedia of conifers, helps gardeners choose just the right plant when investing in these long-term backbones of the garden.
Create tiny, living garden worlds that incorporate shrubs and perennials with the book Gardening in Miniature by Janit Calvo.
Image credit: F.D. Richards/CC BY-SA 2.0