Conifers are beautiful additions to a landscape, adding colour and interest for many years. Many conifers are massive trees that eventually reach 24 m (80 feet) and more. Often, conifers are fast-growers, adding 30 cm (12 inches) of height every year. If space for a towering fir or pine tree is at a premium in your landscape, the pleasure of a conifer can be had by growing them in pots on a patio, porch or balcony.
Tree selection is the most important factor in planting conifers in pots. Don't attempt to plant a full-size conifer in a container, as the tree will outgrow the pot very quickly. Consider a miniature or dwarf variety. Miniature conifers such as "Golden Sprite" cypress, "Sea Urchin" white pine or "Mitsch Mini" mugo pine grow less than 2.5 cm (1 inch) per year, topping out at about 30 cm (1 foot). Alternatively, plant a dwarf conifer that grows between 2.5 and 15 cm (1 and 6 inches) per year, eventually reaching a mature height of 3 to 7.5 m (10 to 25 feet), depending on the variety. Dwarf conifers include "St. James" Norway spruce, "Chippewa" pine or "Gentsch White" Canadian hemlock.
Plant a conifer in a wide, deep container that will accommodate the roots of the mature tree. A small pot will restrict growth, resulting in a smaller tree that will need to be repotted often. Most importantly, use a wide, sturdy container, because a lightweight container may become top heavy and blow over in a strong wind. A container with a drainage hole is critical. Avoid ceramic, clay or other breakable pots in climates that experience freezing winters, as these pots may freeze and crack.
Conifers in pots need a potting medium that retains moisture but is well-drained. Use a commercial potting medium that is rich in compost and other organic materials. The potting medium also should have vermiculite, pumice or perlite to improve drainage. Avoid regular garden soil, which becomes heavy and compacted and won't absorb water efficiently. Garden soil also may have weed seeds, insects and bacteria.
Water and fertiliser
A conifer planted in a pot requires more attention than a tree planted in the ground. Check the tree often, especially during hot, dry weather. Water when the top 2.5 to 5 cm (1 to 2 inches) of soil are dry to the touch. A 5 to 7.5 cm (2 to 3 inch) layer of shredded pine bark or other mulch retains soil moisture and reduces the need for watering. Apply a time-release fertiliser every spring. Use the fertiliser according to the rate applications on the fertiliser package.
Place potted conifers near a wall or other protected area away from harsh winds when the weather turns cold in autumn, as cold winds may cause winter burn. Wrap the pot with an insulating blanket to protect the roots from winter cold.