WHY FRUIT TREES FAIL TO BEAR Page 1 Publication WHY FRUI T TREES FAIL TO BEAR Number 31-S68 AUTHORS: Chuck Ingels, Farm Advisor, Sacramento Co. (Published Edited by: Judy McClure, Master Gardener Program Coordinator October 2000) Fruit trees will normally begin to especially by summer pruning Any factors that cause poor tree bear fruit between two and five (see Training and Pruning Fruit health can affect fruit set and years after planting, depending Trees). Lack of sunlight can also retention. For example, excess or mainly on the species and prevent flowering and fruit set; insufficient water during the method of training and pruning. trees should have at least six summer can cause fruit to drop, Most stone fruits begin to bear in hours of direct sun per day. If you but you would also see drooping year two or three, although are pruning appropriately and or yellowing leaves. Other cherries may not begin bearing your tree is healthy, but still no contributing stresses include root for up to five years after planting. flowers form after several years, constrictions caused by hardpan Apples often begin to bear in consider grafting to a different or compacted soil, sunburn or about two to four years but pears variety or replacing the tree. borer insects on the trunk or can take one to two years longer. Trees that consistently flower but branches, and pests such as soil In addition, fruiting in many set little or no fruit probably lack a nematodes, root rot, bacterial species requires pollination, as pollinizer variety (see Pollination canker, brown rot of twigs, well as adequate irrigation, section below). However, the powdery mildew, and spider drainage, and fertilization. problem could be cold and/or wet mites. OBSERVE FLOWERING AND weather during bloom, which ENCOURAGING PRECOCITY reduces the activity of pollinator RUITING HARACTERISTICS F C insects, preventing the transfer of Trees with vigorous, upright It is important to note whether pollen. Such weather conditions growth, such as cherry and pear, your trees did not bloom at all; also prevent pollen tube growth in tend to begin bearing later than bloomed but did not set fruit; or the female parts of the flower. those with spreading habit, such bloomed and set, but most or all Inclement weather is often more as peach and apricot. However, the fruit fell off at some point of a factor on early flowering these trees can be encouraged to before harvest. If your trees have species such as almond and bear earlier by bending upright never bloomed and they are older plum. Lack of nitrogen can also branches outward during the than the bearing ages listed lead to poor fruit set. If nitrogen growing season, before they above, you may be pruning too deficiency is suspected, fertilize in become too stiff to bend. severely. Most fruit trees require the summer to increase the Branches can be held in the development of spurs or short nitrogen storage in the tree over place by tying them to a shoots on which flowers form, the winter; this stored nitrogen is stake, a string attached although peaches and nectarines utilized for flowering a fruit set the to the ground, or a trellis bloom on longer shoots. It is following spring. (espalier). Also, avoid excessive heading cuts, especially during important, therefore, not to cut off If your trees bloomed and set fruit all the one-year-old spurs and the dormant season, since normally, but the fruit dropped off heading encourages vigorous shoots. It is also prematurely, any of several important to provide growth and reduces flower factors could have contributed. development. Bending adequate light to these Sometimes fruit appears to set, fruiting shoots by unheaded, upright branches but drops in April; this could still outward is a proven method for thinning out crowded be a lack of pollination. growth and/or opening the center, developing spurs and flowers quickly.

COOPERATIVE EXTENSION, UNIVERSITY OF CALIFORNIA Placer County WEB SITE: ceplacernevada.ucdavis.edu Nevada County 11477 E Avenue (Bldg 306, DeWitt Center) 255 So Auburn (Veterans Memorial Bldg)

Auburn, California 95603 The University of California, in accordance with applicable Federal and State law and University policy, does not Grass Valley, California 95945 discriminate on the basis of race, color, national origin, religion, sex, disability, age, medical condition (cancer- PHONE (530) 889-7385 related), ancestry, marital status, citizenship, sexual orientation, or status as a Vietnam-era veteran or special PHONE (530) 273-4563 disabled veteran. Inquiries regarding the University’s nondiscrimination policies may be directed to the UFAXNIVERSITY (530) 889-7397 OF CALIFORNIA COOPERATIVEAffirmative E ActionXTENSION Director, University of California, Agriculture and Natural Resources, 1111 Franklin, 6th Floor, PLACER & NFAXEVADA (530) C 273-4769OUNTIES Oakland, California 94607-5200. (510) 987-0096. E-Mail: [email protected] United States Department of Agriculture, University of California, Placer & Nevada Counties cooperating. E-Mail: [email protected] WHY FRUIT TREES FAIL TO BEAR Page 2

CLIMATE AND WEATHER POLLINATION cherries are self-fruitful, such as ‘Lapins,’ ‘Stella,’ and ‘Sunburst.’ Most fruit trees need a substantial Most fruit trees Many apple varieties are self amount of cold winter weather to need to be fruitful, including ‘Braeburn,’ end their dormancy and to pollinated. Without ‘Empire,’ ‘Fuji,’ ‘Gala,’ ‘Granny promote spring growth. After mild sufficient pollination, Smith,’ and ‘Pippin.’ winters, spring growth and they may blossom flowering are delayed and abundantly, but will SELF-UNFRUITFUL TYPES irregular, the flowering period is not bear fruit. A pollinizer is a “Self-unfruitful” species include extended, and fruit set is reduced. tree or branch of a different many apple, Asian pear, sweet The extended bloom increases variety with a similar bloom cherry, and Japanese plum the chance that inclement period. Pollinators (usually bees) varieties. The label usually weather will cause blossom carry pollen from the flower of one indicates varieties that will diseases, such as brown rot or variety to the flower of another pollinate your tree. fire blight. variety. To pollinate adequately, The chilling requirement is the Most species of fruit trees have plant two or more number of hours below 45°F from ‘perfect’ flowers: both the anthers, varieties no further November 1 through February 15. which contain pollen, and the than 35 to 50 ft. apart - Fruit tree species and varieties pistil, which develops into fruit, the closer, the better. differ greatly in the number of are located in the same blossom. Alternatively, you can hours required to fully break Trees that bear fruit through self- graft a pollinizer dormancy. The label on a pollination, or set fruit without variety onto the tree (see “Bud purchased fruit tree will often pollination, are called “self- Grafting,” EH Note #85). The use state the chilling requirement. fruitful.” However, there are many of bees can improve pollination. The Sacramento area usually fruit species with perfect flowers In the interim before a pollinizer receives adequate chilling, that cannot produce fruit from variety is grafted or planted averaging about 900 to 1,000 their own pollen. These require nearby, you can place flowering hours. When possible, select pollen from another variety and branches of a pollinizer variety in varieties with a chilling are called “self-unfruitful.” a jar filled with water, and set the requirement below about 700 to Some species do not fit into either jar and flowers in the tree canopy. 800 hours, since there are some category. Pistachio and kiwifruit Bees will visit these flowers and years in which we receive less have male trees that produce will pollinate the tree’s flowers. than 800 hours. Varieties pollen and female trees that requiring 1,000 hours or more Some cherries have fairly specific produce fruit. To grow them may set poorly in some years. pollinizer requirements. ‘Bing,’ successfully, it is necessary to Low-chill varieties are available ‘Lambert,’ and ‘Royal Ann’ cherry plant at least one tree of each for most fruit tree species, and the trees do not pollinate one gender near each other. chilling requirement is usually another. Plant a pollinating stated on the label. SELF-FRUITFUL TYPES variety such as ‘Black Tartarian’ or ‘Van,’ or a sour cherry such as Sometimes frost during or shortly Almost all citrus species are “self- ‘Montmorency’ nearby. after blossoming can cause fruitful.” Other self-fruitful species young fruitlets to abort, even include quince, sour cherry, most For additional information on though no frost damage is seen. apricots, fig (except the Smyrna pollination and varieties, see When a heavy frost is expected, type), peach (except ‘J.H. Hale’ these Web sites: covering the trees with plastic or and some others), and European- Fruit and Nut Research & bed sheets will sometimes type plums and prunes. Some Information Center prevent injury to the expanding European pears are also self- Dave Wilson Nursery buds or blossoms, providing fruitful. ‘Bartlett’ pear is temperatures do not fall too low parthenocarpic, which means that and the cold weather is of short no pollination is required to set duration. fruit (only in California). Some

UNIVERSITY OF CALIFORNIA COOPERATIVE EXTENSION PLACER & NEVADA COUNTIES WHY FRUIT TREES FAIL TO BEAR Page 3

BIENNIAL BEARING Biennial bearing of apples is difficult to alter or correct. Occasionally, certain fruit However, you can induce a return trees such as apples bear to normal annual fruit production heavily one year and by heavily thinning during the year sparsely the next. This is in which the trees are producing called “biennial bearing.” their large yield (see “Fruit The spring-flowering buds of most Thinning to Increase Fruit Size and deciduous fruit trees have actually Maintain Healthy Trees,” EH Note been formed during the previous #84). About 30 to 40 healthy summer. Therefore, an especially leaves are needed to produce heavy crop one year may prevent each fruit. adequate flower bud formation for the following year because the Adapted from Environmental carbohydrates produced through Horticulture Note #68, University of photosynthesis are used California Cooperative Extension, preferentially for fruit production Sacramento County during the “on” year.

UNIVERSITY OF CALIFORNIA COOPERATIVE EXTENSION PLACER & NEVADA COUNTIES