People frequently want to grow some type of fruit tree in a container, usually because of poor soil, improper climate or lack of sufficient space as is often the case around apartments and condominiums. Fortunately, a wide variety of fruit trees can be grown in containers with some degree of success. However, such plants will rarely be as attractive or grow and fruit as well as those grown under optimal conditions in the ground.
One of the principal reasons for growing fruit trees in containers is portability. Thus, tropical and subtropical fruits can be grown in containers in areas where freezes might occur. The size and mobility of the containers allows the plants to be moved indoors during periods of predicated freezing temperatures. Many fruits which can be successfully grown in containers are listed in Table 1. Most will produce some fruit if given proper care. The list is by no means complete, as most fruit trees could be grown in containers if the size of the container were not a problem. [The wider availability of many types of dwarf fruit trees also greatly increases the choices that container gardeners have.]
Containers may be plastic, metal, clay, ceramic, wood or any others normally available at nurseries and garden supply stores. Used whisky barrels cut in half are excellent or wooden boxes may be built to order. The container should have adequate holes at the bottom for drainage of excess water.
The drainage holes of the container may be covered with pieces of screen mesh to prevent the soil from washing out. A layer of gravel 1-2 in. (2-5 cm) should be placed in the bottom of the container to facilitate drainage.
Any commercial potting soil should be suitable for growing fruit trees. However, a mixture of 1 part sand, 1 part peat and 1 part bark, perlite or vermiculite will also serve quite well. The potting medium should be loose enough to permit adequate but not excessive drainage.
Examine the root system of the plant. If it is pot-bound or has experienced severe root crowding in its previous container, judiciously prune some of the larger roots and loosen others to facilitate root proliferation in the new container.
The container should be partially filled with soil (large containers should be filled at the site they are expected to remain). Place the plant in the partially filled container of soil to its correct planting depth which is the depth at which the plant was previously grown. The final soil surface should be 1-4 in. (2-10 cm) below the rim of the container, in direct proportion to container size, to allow for watering.
Complete filling the container and firm the soil around the plant. Water thoroughly but do not fertilize until new growth commences. An attractive mulch of bark, gravel or other material can be added to improve the appearance of the container.
Most fruit crops grow best in full sunlight, but some will do well in partial shade. However, plants grow in direct proportion to the amount of light received, if other conditions are optimum, so container grown fruit trees should be placed where they will receive maximum sunlight.
It is important that rapid changes in light exposure be avoided, i.e. plants growing in partial shade should not be suddenly exposed to complete, direct sunlight. Any plants that are to be grown indoors part of the year should be acclimated by gradually reducing the light to which they are exposed for 2-23 weeks before moving them inside and vice versa for plants being moved outdoors. Such acclimation is not necessary for plants that are to be moved indoors for few days during freezes.
Tropical and subtropical fruit trees cannot tolerate freezing temperatures for very long. Some will be killed back to the soil by mild freezes while only small twigs will be killed on others. Some root damage can occur because the root system is not as well insulated from cold in a container as it would be in the ground.
Cold hardiness depends on the plant, the care it receives and many other factors. Protection from severe cold is essential for all tropical and subtropical fruits growing in containers. Plants may be covered temporarily with blankets, paper or other material as protection against hard freezes, but such material should be removed each morning to allow the plants to take full advantage of incoming solar radiation. Plants moved indoors during cold spells should be placed away from drafts caused by doors and heating ducts.
Most container grown plants that do not thrive are usually in poor condition due to faulty watering practices, usually overwatering. Plants growing in containers should be watered only as needed. The frequency of watering depends upon such variables as type and size of plant, type and size of container, temperature, humidity, potting medium and other factors. For most plants, the upper surface of the soil should be allowed to become dry to the touch before watering. Then water thoroughly by slowly filling the container. Good drainage of excess water from the container is essential.
The soil in plastic, metal and ceramic containers generally stays wet longer than it does in wood or clay containers, which allow water to evaporate through the sides. Cool weather generally slows plant growth and this reduces the plant's need for moisture, so watering should be less frequent during cool weather.
Good nutrition is essential to the success of container-grown fruit trees, but excess fertilizer can result in overgrowth, poor fruit and possible dieback due to salt accumulation. Water-soluble fertilizers are widely available and should be used according to label directions. If mature foliage is deep green in color, adequate fertilizer is being used.
Many fertilizers can be used successfully, provided they are complete and balanced. The fertilizer should contain nitrogen, phosphorus and potassium in balanced proportions and should include lesser amounts or traces of magnesium, iron, manganese, zinc and copper. The ingredients and quantities of each nutrient contained are listed on the fertilizer label.
Salt accumulation may sometimes be a problem and is often indicated by a white crust on the soil or container and may be due to excess fertilization and/or water containing considerable soluble salts. Should this occur, the container should be thoroughly leached by slowly running water through the container for several minutes. This will carry excess salts down through the soil and out the drainage holes.
With few exceptions, fruit trees will develop and maintain their natural shape with little or no training or pruning. They will occasionally become "leggy" when grown indoors or in poor light for too long. Leggy branches should be partially cut back to force branching and bushiness.
Frequently, the top will grow rather large and begin to exceed the capability of the root system. Consequently, some leaf shed and twig dieback will often occur. Such plants should be pruned back heavily to rejuvenate them. When plants area heavily pruned, less fertilizer and water will be necessary to compensate for the reduced plant size.
Most fruit crops will produce fruit in containers, given time, good care and adequate size and age. However, naturally large fruit trees will require larger containers to bear much fruit, as the amount of fruit produced is proportional to the plant's size, so large yields should not be expected. Many fruit plants need to be large in order to fruit at all, so their size can quickly become limiting in containers. Many fruit crops also require the presence of pollenizer cultivars and pollinating insects. Flowers can be pollinated by hand.
It must be emphasized that even under the best of conditions, fruit production in containers will not equal the quantity produced on trees in the ground, as fruit trees grown in containers are usually growing under sup-optimal conditions.