Chilling Requirement - Stone (prunus) Fruit Tree Selection Guidelines To Match Local Weather Conditions

Stone (prunus) Fruit Tree Selection Guidelines To Match Local Weather Conditions

When discussing prunus fruit trees (almonds, apricots, cherries, nectarines, plums, peaches,) there are several climate guidelines to follow for maximum crop yield.

• Select varieties that have a chilling requirement at least 20% less than local averages.
• Selecting a low chill variety in a cold area will result in trees flowering too early and being damaged by late frosts.
• Selecting a high chill variety in warm areas will result in little or no fruit production.
• Early flowering varieties are best in warm climates, late flowering varieties are best in cooler areas.
• Early ripening varieties are best in areas with intense summers, late ripening varieties are best in cooler summers.
• Climate extremes may eliminate certain varieties that would otherwise meet the chilling requirements. For example, the very dry air and intense summer heat as found in Phoenix Arizona may stress a fruit tree beyond its ability to produce quality fruit.
• Terrain can affect the chilling hours received. Open slopes may receive more chilling hours than sheltered areas next to warm buildings.
• Various sellers of fruit trees publish significantly varying chilling hour requirements for the same variety. It is difficult to know the exact requirements. Experiment and ask around for promising local cultivar success stories.

Following the above guidelines here is a practical example. A good apricot for Phoenix Arizona (350 chilling hours) would be Katy apricot with a 200-300 chilling hours requirement. It is early blooming and ripens in May and the tree itself thrives in the intense dry desert heat with adequate regular irrigation. The Katy apricot has no apparent pests or disease problems locally. Planting a Katy apricot only 100 miles north (1000+ chill hours) would likely be fruitless from late frost damage to the flowers. A late ripening apricot variety like Autumn Glo might be a bad choice for Phoenix because the intense long summer heat (115+) might cook the green fruit on the tree and result in strange tastes and other problems with late ripening. The same late ripening variety might also fail in the colder areas 100 mile north because of the shorter summer not allowing enough time to properly ripen before cold weather sets in. A better apricot choice for that colder area might be Goldcot with an 800 chill hour requirement. The late ripening Autumn Glo might be better off in a long cool summer climate along the west coast.