Worldwide, citrus trees produce more fruit than all other deciduous fruit trees combined. Many gardeners in Marin find growing citrus rewarding, but somewhat problematic. For problem-free growth and development, citrus plants require adequate sunlight, water, nutrients and temperatures between 65 and 85 degrees. Key preventive management practices include choosing an appropriate growing site, preparing the site well before planting, providing appropriate irrigation and drainage systems, selecting disease-resistant cultivars and rootstocks certified to be pathogen-free, using good sanitation and providing appropriate cultural care.
To successfully grow citrus plants, learn which varieties grow best in your area’s microclimate and purchase plants only from a reputable nursery. As citrus trees are subtropical to tropical in nature and suffer severe damage or even death in freezing temperatures, choose a variety that has sufficient cold-hardiness. The tree you select should have healthy, deep green leaves, and the trunk should be straight and able to support the tree without stakes.
Citrus does best in slightly acidic, well-drained loam or sandy loam soils, but with proper irrigation that drains easily, could grow well in clay soils. Plant trees in the spring in a warm, sheltered, preferably south-facing position away from cold winds; cover plants in winter if temperatures fall below 29 degrees. Choose a site that receives full sun for at least six to eight hours. To reduce the chance of disease, plant trees so the top of the root ball is an inch above the level of the native soil. Manure or soluble fertilizer should not be placed in the planting hole because it can injure roots.
Proper irrigation is one of the most important cultural practices to help young trees become established. Care must be taken to keep the soil moist, but not water-logged. Newly planted trees need to be watered every three to seven days depending on weather conditions and soil type. Water when the soil begins to dry out a few inches below the surface. After trees become established, water thoroughly but reduce the frequency to every seven to 14 days. A layer of organic mulch, kept a foot away from the trunk, will help retain soil moisture and permits feeder roots to grow close to the surface.
Nitrogen is the most important nutrient for citrus as it is required for flowering and fruit set. Apply a nitrogen fertilizer in January or February just prior to bloom. To maintain growth and fruit production, a second application can be applied in May; a third in June; avoid late-season fertilization. Occasionally, citrus suffers from zinc or iron deficiency. This can be quickly addressed with a foliar application of a liquid chelated micronutrient solution, but the long-term solution is to check the soil pH, to be sure it’s between 6.5 and 7. If the pH is correct, add appropriate soil amendments. If it’s not, adjust the pH.
To reduce the chance of infection, pull weeds and remove damaged fruit. Prune away dead, diseased or broken branches.
Monitor trees regularly to detect pests before serious injury occurs. Common citrus pests include citrus leaf miner, scales, Botrytis, slugs/snails and rats. Reduce the chance of infection by occasionally washing both sides of the leaves with a vigorous spray of water. Use an appropriate biological insecticide (Neem oil or Spinosad) if necessary.
Most citrus fruit should be allowed to ripen on the tree — the longer it remains on the tree, the less acidic and sweeter it will become. While enjoying years of delicious fruit, feast on the fact that citrus requires minimal pruning, no fruit thinning and can be adapted to small spaces. And, in comparison with other fruit trees, citrus has relatively few pest and disease problems if provided with good cultural care.