Answer: The cherimoya is subtropical or mild-temperate and will tolerate light frosts. Young growing tips are killed at 29? F and and mature trees are killed or severely injured at 25? F. If cherimoyas do not receive enough chilling, the trees will go dormant slowly and then experience delayed foliation. The amount of chilling needed is estimated to be between 50 and 100 hours. The tree grows well in the coastal and foothill areas of southern California, doing best at a slight elevation, 3 to 15 miles from ocean. It is worth attempting in sunny, south-facing, nearly frost-free locations from San Francisco Bay Area to Lompoc, and may survive to fruit in a very few protected Central Valley foothill locations from Chico to Arvin. Resentful of the excessive dry heat of the interior, it is not for the desert. Cherimoyas are not recommended for container culture because of their tap root type root system.
Location: Cherimoyas prefer a sunny exposure, buoyant marine air and cool nights. In southern California do not plant where heat collects on barren hillside or against a wall, since the leaves and fruit may sunburn badly. In the north, do the opposite: plant against a south facing wall to collect heat and encourage early bud-break and fruit ripening. The trees need protection from constant ocean or Santa Ana winds which may damage them and interfere with pollination and fruit set.
Soil: The cherimoya performs well on a wide range of soil types from light to heavy, but seems to do best on a well-drained, medium soil of moderate fertility. The optimum pH ranges from 6.5 to 7.6.
Cherimoyas need plenty of moisture while they are growing actively, but should not be watered when they are dormant. The trees are susceptible to root rot in soggy soils, especially in cool weather. Commence deep watering biweekly in April. Drip irrigation is also an excellent way to supply water. It is best to avoid poor water to prevent salt build-up. Drought-stressed trees will drop their leaves, exposing the fruit to sunburn.
Cherimoyas should be fertilized on a regular basis. Apply a balanced fertilizer, such as 8-8-8 NPK, in midwinter, then every three months. Increase the amount of fertilizer each year until the trees begin to bear fruit. Mature trees require an annual application of 4 ounces of actual nitrogen per inch of trunk diameter. Cherimoyas also respond to organic amendments. It should be kept in mind that yellow leaves may mean that the soil too dry or the weather too cold, not always a need for fertilizer.
Cherimoyas have rather brittle wood. Prune during the dormant period to develop strong branches that can support the heavy fruit. Train the tree to two scaffold branches at 2 feet of trunk, pruning them to a 2 foot length. Save only the strongest single shoots, preferably those at 60 to 90 degree angle, and remove the others. In the following years, remove two-thirds of the previous year's growth, leaving six or seven good buds, at time of new growth. This will keep fruiting wood within reach of the ground. Thin out crossing branches.
Young trees are very frost sensitive. Wrap the trunk and scaffold with sponge foam for protection, or cover the entire tree. In cooler areas plant next to a south-facing wall or under the eaves to trap house heat.
Mealybugs and snails are the main pests of cherimoyas. Keep ducks or apply copper strips to the trunks for control of snails. Mealybugs are brought by ants which can be controlled to some extent by maintaining fresh Tanglefoot on masking tape around the trunk. The masking tape is important to prevent damage to the tree. Skirt the tree to prevent ant access from the ground or weeds. No chemicals are registered for use on Cherimoyas.
Cherimoyas are susceptible to Armillaria (Oak Root Fungus) and Verticillium. Do not plant in old vegetable gardens, or near tomatoes, eggplant or asters. Crown rot can kill trees damaged by frost or growing in saturated soil, as well as from trunks hit by frequent, superficial lawn sprinkling.
The yellowing leaves probably indicate a soil problem, not a need for fertilizer.
Hope this information is helpful!
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