Container Fruit Trees
Fruit trees in containers require more care than fruit trees planted in the ground. Generally, fertilizing should be done more often, especially for citrus. Watering must be done more frequently, two to three times a week during spring, then almost daily watering during the hot summer months.
Generally, the larger the container, the less frequent you will have to water. Smaller containers generally dry out faster than larger containers. The more wind your plants are exposed to, the more water they will need. Wind can dry your containers out quickly, even if it isn't a particularly warm day.
Growing Fruit Crops in Containers
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.
Containers can be just about anything. Used whisky barrels cut in half are fine. 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 inches (2-5 cm) should be placed in the bottom of the container to facilitate drainage.
Fertilizer
Good nutrition is critical to 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.
Pruning
With few exceptions, fruit trees will develop and maintain a natural shape with little pruning. Frequently, the top will grow rather large and begin to exceed the capability of the root system. Such plants should be pruned back heavily to rejuvenate them.
Fruitfulness
Most fruit crops will produce fruit in containers, given time, good care and adequate size and age. Many fruit trees also require pollinating insects. Flowers can be pollinated by hand. 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.
Leaves Turning Yellow
Yellow leaves could be a result of lack of fertilizer and minerals, a watering problem or insect damage. If the older leaves are turning yellow and the other leaves are a pale green, then you may need to add nitrogen. If the leaves are yellowing, but the veins on the leaves are green, then your citrus most likely needs iron. If the outer leaves are yellowing and some of the branches are dying back, the citrus may be getting too much water.
Insect Problems
Insects that abuse citrus are aphids, scales, and mites, brought to the trees by ants. A trail of ants going up your lemon tree means there are probably aphids or scales in your tree.
Another indication of these insects is a sticky residue on the leaves. Most of the insects will be found on the back side of the leaves. Scales may be found along the branches as well and will look like bumps along the limbs. Scale can be white, black or brown. These insects are seen most often in the spring and fall, but can be a problem at any time of the year. For control of these insects, you can use Horticultural Spray Oil, Malathion, or a Pyrethrin based spray (like Master Nursery Pest Fighter Spray).