Trees in pots

Flower & Garden Magazine, August-Sept, 1995 by Marty Ross

PATIO GARDENERS HAVE LONG KNOWN THE pleasures of plants grown in pots. Containers allow the gardener to place color and fragrance just where it is needed. Flowers, vegetables and herbs are easy to grow in pots of all kinds. To add a new dimension to container gardening, try a tree.

Container-grown trees are not a new idea. Early garden book illustrations show trees in pots in 15th century gardens. By the late 17th century, tender specimens were grown in containers all over Europe; orange trees in tubs dotted the garden of Versailles every summer. Louis XIV's exotic trees were moved into a warm orangerie in winter, but all trees in containers do not demand such special treatment. A potted tree chosen with an area's climate in mind should be able to hold its place in the garden year-round.

Trees are the strongest vertical elements in the structure of most gardens. They provide shade and privacy, and give the garden much of its character. Planted in pots, they simply become more versatile, allowing height and dramatic emphasis to be added wherever it is needed.

Planting can be done at almost any time, but try to. allow several months for the tree to become well established before the season of most severe weather in your area. In cold climates, plant in spring or summer. Where winters are mild, fall and winter planting may be ideal.

Although trees in pots will remain smaller than normal, they should have room to grow without looking tortured -- potted trees should have a grand presence. In places where bone-chilling winters could freeze the soil and the tree's roots, use containers at least 18 inches tall and wide. If the winters are severe enough to crack and break ceramic pots, stick to sturdy plastic or wooden containers. Some experts recommend the additional insulation of an inch-thick layer of plastic foam (sold at hobby shops) all around the inside of a tub in cold climates.

Choose a pot or tub that complements its surroundings. Wood looks attractive in any setting, and it can be painted white to stand out, or a rich and soothing green, or a color that matches the house's trim. Dark colors may not be appropriate for pots exposed to hours of direct sunlight; the tree's roots may bake in a hot pot. Probably no container will last forever, but some are more ephemeral than others; bushel baskets, even those lined with plastic. fall apart after a year or two in the garden. Whiskey barrels seem to last for years. If you build the container yourself, use 3/4-inch-thick wood and galvanized or brass screws.

Good drainage is crucial to all plants in pots. Drill holes in the container if it does not have them already. If the holes are large, place pot shards over them to keep the soil from washing through.

Decide where the container will go before you plant. To experiment with several sites, move the empty container around, using a broomstick or garden stake to represent the tree. The tub. tree and soil will be too heavy to lift after you plant; planks and rollers may be needed to move it even a short distance.

Set the tub on bricks or blocks of wood, if possible, to encourage good drainage, allow air circulation, prevent rot and help guard against the roots' growing through the drainage hole and into soil below. In winter, this air space may need to be blocked with leaves or straw.

In the ground, trees send their roots far and wide to ensure a constant supply of moisture and nutrients. In a pot, they rely on the nutrition and moisture you provide. Start with a mix of equal parts of good garden soil and compost, with a few handfuls of dehydrated manure added. Mix the soil on an old bedsheet or sheet of plastic next to the container. If your garden soil compacts easily or does not drain well, add perlite, vermiculite or fine bark chips to lighten the mix.

Once you have a sturdy container, a supply of soil and a site picked out, select a tree. Any tree hardy in your climate zone -- and remember the garden's microclimates -- should thrive in a pot. Choose a healthy plant with a pleasing shape that fits your needs. Buy something with a little flair; trees in pots really stand out.

Many trees are suitable for containers. Good evergreens to try are pine, yew and juniper. Hollies, spring-flowering cherries, crape myrtle, magnolias of all kinds, willows, even ginkgoes thrive in pots. Birch, locust and maple trees, especially Japanese maples, also are good choices. Where winters are very mild, try orange, lime or grapefruit. Think about what you want the tree to do and the light and exposure where the container will be placed, then discuss the possibilities with experts at your nursery. They may recommend specific varieties for your area.

To plant, first discard the container or burlap around the root ball. Loosen the soil around the roots with your fingers, thereby encouraging the tree's roots to grow into your potting medium. Lift the tree by the root ball, not by its trunk, and set it on a layer of soil in the tub. Fill in with soil, gently firming it around the roots as you go. Plant the tree only as deep as the soil line on its trunk, and leave a couple of inches to spare at the top of the container. Water thoroughly after planting.