Citrus trees are one of my favorite choices for almost any garden. They are evergreen, prolific, and relatively low maintenance. And they just make a garden look sunnier!
Selecting and Planting
In climates where frosts do not occur, citrus (Citrus spp.) can be planted at any time. Elsewhere, plant trees in early spring.
Citrus is best suited for USDA zones 8 to 11. Best results come from planting in full sun, but they can tolerate some shade in most areas and do well with afternoon shade in the hottest regions. The general rule of thumb is that sweeter citrus types need more heat and sour types need less. Lemons, kumquats, and mandarin oranges are the most shade tolerant, but they still need heat.
Heat isn’t the only factor to consider, though. Frost-hardiness is an issue as well. Citrus will only survive in areas where temperatures never drop below 20°F. Lemons, limes, and citrons are the most frost-sensitive and also require the least heat. The most frost-hardy citrus includes satsuma mandarins, sour oranges, calamondin, and kumquats. Sweet oranges, grapefruit, mandarins, and the 'Improved Meyer' lemon fall somewhere in between on the frost-hardiness/required heat scale.
Well-drained soil is essential for citrus, which have thin-skinned trunks that will rot easily if the ground stays soggy. They prefer slightly acidic soil (pH level of 6 to 7.5) and lots of organic matter.
Standard trees grow to 20 to 30 feet high. Dwarf trees can grow to 5 to 10 feet, but careful pruning can maintain them at a much smaller size for container growing. Dwarf citrus trees can do well in large containers and can be brought inside or to a protected area when freezes are predicted.
To plant, dig a hole twice as wide and the same depth as the root ball. Add compost to the hole and to the soil that will be filled back in. Position the tree, making sure that the graft union at the bottom of the trunk is above the soil line. Water thoroughly so that the water penetrates the root ball and any air pockets in the soil will be filled in. Mulch deeply around the tree, but be careful that the mulch is kept a few inches away from the trunk to avoid crown rot. If planted in a lawn area, remove the lawn all the way out to the drip line of the tree.
Citrus needs consistent moisture but overwatering, particularly in areas with poorly draining, clay soil, will kill the tree. Newly planted and container-planted trees should be watered a couple times a week in summer, more during heat waves. Established trees can get by with watering every other week in the summer. Allowing the soil to completely dry out between waterings can cause the fruit to split.
Regular feedings of a high-nitrogen fertilizer are needed for all citrus, but in areas with sandy soil, use a balanced fertilizer. If leaves turn yellow between the veins, the tree is suffering from chlorosis and requires supplemental iron, manganese, or zinc. Apply a foliar spray that contains all three minerals.
Citrus mostly needs pruning only for shaping or removing dead or crossing branches. The best time to prune is summer, although light pruning can be done in spring and fall in areas that are not likely to experience early or late frosts. Avoid pruning so heavily that you expose the trunk to sunburn, but do be vigilant about removing suckers that sprout from below the graft union.
Pests and Diseases
Some of the most common pests on citrus are sucking insects such as aphids and scale. They thrive on the juicy evergreen leaves and stems, although it takes a heavy infestation to seriously harm the plant. On smaller trees these pests can usually be controlled by blasting them with a jet of water from the hose or wiping them off with a paper towel soaked in rubbing alcohol. If you have a problem with aphids or scale, you'll probably also find you have a problem with ants, which “farm” the insects for the sticky honeydew they secrete. If you control the ants—best done by applying a sticky band around the base of the tree using a product like Tanglefoot--you can better control the aphids and scale. Other insects, such as mites, can be controlled by spraying with horticultural oil in the spring and fall (or just in fall in hot-summer regions).
There is one particular citrus pest that home growers should be on the lookout for. The Asian citrus psyllid is a winged insect, similar to an aphid, that carries a bacterial disease called huanglongbing, also known as citrus greening disease. The disease is not harmful to humans but ruins the taste of citrus fruit and its juice and will eventually kill the infected tree. There is no cure for the disease so the only way to manage it is to control the spread of the psyllid. So far, the insect has done major damage to citrus trees in numerous states throughout the entire southern United States and west coast.
To prevent the further spread of the insect and the disease, go to www.CaliforniaCitrusThreat.org for the latest updates and guidelines.
Other diseases that may affect citrus trees include:
- Sooty mold: A fungus that lives on the honeydew secreted by sucking insects such as aphids. It appears as large black patches on leaves. The best way to control it is to control the pests that secrete the honeydew. Insecticidal soap will help to wash off the pests as well as the mold.
- Citrus canker: A bacterial disease that can spread in wet, windy conditions. The disease causes spots on the leaves and fruit; serious infection can lead to defoliation and fruit drop. Application of a copper-based Bordeaux spray can provide some protection.
Citrus generally ripens in late fall through winter, although Valencia oranges and some other varieties don’t ripen until spring or summer. Lemons and limes are considered everbearing but produce the most fruit in winter and spring.
Color of the fruit is not a good indicator of ripeness; you have to taste it to know for sure and since citrus will only ripen on the tree, don’t harvest without tasting first. Ripe fruit will feel a bit heavier than unripe fruit and the peel will feel less stiff when pressed.