Many dwarf conifers make excellent container plants and can add year-round interest. When choosing your conifer, look for slow-growing plants (1 to 6 inches of growth per year). Also, pay attention to the shape of the conifer; there are spreading conifers that may not be suitable for containers, while mounding or upright forms make beautiful additions to your container garden.
Choose a container that is at least 4 to 6 inches wider than the container or root ball the conifer came in.
People generally place pieces of broken terracotta pots over and around the drainage hole to prevent the holes from clogging. If you want to increase the weight of the container, you can fill approximately a tenth of the planter with small stones. Weight at the bottom of the container is important as conifers can become top heavy and blow over in strong winds.
Add a small amount of soil-based mix to the container. Use a combination of soil-based mix and sharp sand (3:1½ or 3:2 ratio) for good drainage.
Gently loosen the roots of the conifer with a hand fork or your fingers.
Place the conifer in the container making sure that there is a space of at least 1 inch between the rim of the container and the soil surrounding the roots
Add the rest of the soil mix to the container and water the plant well.
Add a layer of fine gravel or mulch to prevent water evaporation.
Most dwarf conifers can remain in the same container for several years. Conifers can be planted as a specimen in a container or you can create a miniature landscape with a variety of containers. For city dwellers, pines and junipers fare well in more exposed sites. Choose a heavy container, such as terracotta or a wooden barrel, to give the plant stability.
When choosing a conifer at a garden center, remember that container-grown conifers tend to do better than conifers bought as root-balled plants. The latter was grown in the ground and contains soil organisms that may lead to problems in the confines of a small container.
Feed conifers during the summer with an all-purpose fertilizer; slow-release fertilizers tend to be the most efficient. Remember to water your container regularly so that it does not dry out.
The fine foliage of Pinus strobus 'Shaggy Dog', a spreading dwarf pine
Designing with Conifers by 
Encyclopedia of Conifers by 
The Complete Container Garden by 
The Homeowner's Complete Tree and Shrub Handbook by 
