Chilling Requirements of Fruit Trees Growing at Cloverfield Organic Farm

Our farm is located in Sunset Garden Zone 17, in El Sobrante, California. Our geographic location means we have a relatively mild climate with significant coastal influence, fairly cool Summers, and low amounts of accumulated chilling hours in the Winter. Our USDA zone is 10A. Our mild climate dictates what fruit crops will grow and produce good quality and high yields of fruits at our farm.

Accumulated chilling hours are the hours during the months of November to February, when the fruit trees are dormant, and when the outside temperature is between 32 and 45 degrees Fahrenheit. Here is a chart showing the chilling hours for an adjoining city of El Cerrito. Our chilling hours might be a bit more in the lower parts of our farm valley, where cool air collects, than what is shown in this chart for neighboring El Cerrito.

Calculators - Fruit & Nut Research & Information Center (ucanr.edu)

As you can see from the chart, accumulated chilling hours over the last few years have varied from as low as 207 hours to as high as 590 hours. This last 2021/2022 Winter we had 396 chilling hours. In 2014 the chilling hours were only 128!! Several different fruits have very low chilling requirements (i.e., 150 hours or less). Some of these are pomegranates, citrus trees, figs, mulberries, and persimmons. All of these do well at our farm and produce every year.

If a fruit tree doesn't get the required chilling hours that it needs during the Winter dormant season, the tree may have either no or erratic flowering. The health of the tree may be weakened also. Chilling below what the tree needs may prevent or reduce fruit setting.

In some cases we have planted some fruits that require more chilling hours than what our Winters may reliably provide, realizing that the yields may be lower or only possible during certain years. One tactic we use for the higher-chill fruits is to plant them lower in our valley or in more shaded Northern exposures so that they get more cold exposure. There is a trade-off we make if a fruit is one we really enjoy but needs more chilling hours; we may try growing this fruit tree even if we can only harvest fruits from it intermittently.

Fruit tree breeders and propagators have been developing more low-chill fruits in the expectation of climate warming. Here is a chart of the various low-chill fruits we have planted at our farm:

Type Variety Expected Harvests: Chill Hours:

Lemon Meyer Lemon 1/1 - 12/31 0

Orange Washington Navel Orange 1/10 - 2/25 0

Orange Moro Blood Orange 1/15 - 3/15 0

Orange Trovita Orange 2/25 - 4/30 0

Grapefruit Rio Red Grapefruit 3/1 - 5/1 0

Mandarin Tango Mandarin 3/15 - 4/20 0

Orange Valencia Orange 3/15 - 5/15 0

Mulberry Pakistan Mulberry 5/27 - 6/12 0

Avocado Mexicola Avocado 8/15 - 9/10 0

Mandarin Satsuma Mandarin 10/21 - 1/15 0

Lime Bearss (Persian) Lime 11/1 - 4/10 0

Guava Nazemetz Pineapple Guava 11/15-12/15 0

Cactus Pear Burbank Spineless Cactus Pear 11/15 - 12/31 0

Lime Australian Finger Lime 11/15 - 2/1 0

Orange Robertson's Navel Orange 12/20 - 1/25 0

Orange Cara Cara Orange 12/20 - 1/25 0

Blackberry Blackberries 6/25 - 8/20 100

Apple Dorsett Golden Apple 6/25 - 7/20 100

Fig Negronne Fig 8/10 - 11/20 100

Fig Osborne Prolific Fig 9/05 - 11/20 100

Fig Brown Turkey Fig 9/05 -11/20 100

Fig Desert King Fig 9/05 - 11/20 100

Fig Black Mission Fig 9/05 - 11/20 100

Loquot Gold Nugget Loquot 5/15 - 5/30 150

Jujube Lang Jujube 9/5 - 10/5 150

Pomegranate Hotuni Zigar + Other Pomegranates 9/13 - 11/3 150

Jujube Li Jujube 9/15 - 10/10 150

Olive Empeltre Olive 1/20 - 2/21 200

Blueberry Colibri Blueberry 4/2 - 6/15 200

Strawberries Sequoia Strawberries 4/22 - 7/15 200

Currant Wilder Red Currant 6/3 - 6/20 200

Apple Anna Apple 6/25 - 7/20 200

Peach Tropic Snow White Peach 7/1 - 7/15 200

Elderberry Emerald Lace Elderberry 7/3 - 9/26 200

Elderberry American Black Elderberry 7/15 - 8/15 200

Guava Chilean Guava 8/19 - 10/5 200

Persimmon Jiro Fuyu Persimmon 10/15- 10/25 200

Olive Various Table/Oil Olives 10/15 - 12/15 200

Persimmon Hachiya Persimmon 10/20 - 11/10 200

Cherry Royal Lee Cherry 5/5 - 5/15 250

Cherry Minnie Royal Cherry 5/10 -5/25 250

Cherry Royal Crimson Cherry 5/12 - 5/28 250

Plum Green Wild Plum 5/16 - 6/10 250

Plum Ripe Wild Plums 6/1 - 9/5 250

Peach Donut (Stark Saturn) White Peach 6/25 - 7/10 250

Peach Babcock Peach 7/5 - 7/20 250

Peach Mid Pride Peach 7/10 - 7/25 250

Peach Red Baron Peach 7/18 - 8/10 250

Pear Shinseiki Pear 8/10 - 10/5 250

Apple Sundowner Apple 9/15 - 10/5 250

Medlar Karadagskaya Medlar 9/20 - 10/20 250

Pluot Splash Pluot 6/20 - 8/10 300

Pluot Dapple Supreme Pluot 7/5-7/20 300

Plum Burgundy Plum 7/8 - 7/21 300

Nectarine Double Delight Nectarine 7/10 - 7/25 300

Plum Late Santa Rosa Plum 7/15 - 8/1 300

Plum Laroda Plum 7/18 - 7/28 300

Pear Hosui Pear 7/25 - 8/10 300

Autumn Berry Autumn Berry 7/25-10/15 300

Grape Marechal Foch Grape 7/28 - 8/15 300

Grape Gewurtztraminer Grape 7/28 - 8/10 300

Grape Emeryville Pink Grape 8/10 - 9/10 300

Grape Black Monukka 8/13 - 9/20 300

Peach Fairtime Peach 8/20 - 9/05 300

Quince Smyrna Quince 9/8 - 9/25 300

Walnut Pedro Walnut 9/20 - 10/15 300

Aprium Cot-N-Candy White Aprium 6/25 - 7/5 350

Pluot Flavor Grenade Pluot 7/12 - 8/10 350

As you can see, we expect to have ripe fruits available for visitors to come u-pick most weeks of the year. Some years will be better than others based significantly on the amount of chilling hours, the warmth of the Summer season, and amount of rainfall/ humidity. Farming is a delicate and intricate science with many variables impacting our success at producing a wide variety of delicious farm fresh organic fruits.