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Marin IJ Articles

Why didn’t my fruit tree set?

  • Martha Proctor
  • Did your fruit tree not produce much fruit this year? Let’s look into why this might occur.

    For the home gardener, the number one reason for failure of trees to bear fruit is improper tree vigor. Over vigorous trees expend all their energy in growing wood and don’t produce flower buds. Typically, this occurs for two reasons: over-fertilization and over-pruning. Heavy applications of nitrogen (are you fertilizing a lawn within 5 feet of the spread of the tree’s ranches?) will stimulate excessive growth at the expense of flower production. Heavy winter pruning also stimulates excessive growth. Fruit trees (with the exception of citrus) should be pruned each winter, but indiscriminate heading cuts (the removal of a portion of the branch) will delay flowering and fruiting as pruning promotes more vegetative growth and delays flowering. The best time to prune citrus trees is soon after harvest in winter to early spring before bud break.

    A second leading cause for poor fruit production is frost damage. The flowers of fruit trees are very sensitive to late spring frosts. Temperatures below 29oF prevent fruit formation. Once the flower buds begin to swell and develop there is a risk of frost damage. Examine the flowers the day after a frost - those with dark brown to black centers will probably not set fruit that year. To avoid this, select fruit trees adapted to your area and plant them on the most frost-free, weeded, adequately irrigated section of your property. Extremes in temperatures during the winter months can also damage flowers. Warm winter temperatures followed by sudden drops in temperature usually kill the flowers if they are still dormant.

    A third reason for failure is lack of, or poor, pollination. Fruit will not form until pollen from male tree parts are transferred to the female parts of a flower. Without pollination, flowers may bloom abundantly, but will not bear fruit. To produce fruiting, flowers must receive healthy pollen at the proper time. Bees are the main method for the transfer of pollen between flowers. Anything that interferes with bee activity, such as insecticides, strong winds, or rain or cold weather will reduce pollination. Most apple, plum, sweet cherry and pears are cross-pollinating or self-unfruitful. This means they need another tree for pollination, a tree that is within 100 feet and is a different variety of the same fruit. Some trees produce sterile pollen and need to be planted with at least two other varieties. The main agents that transfer pollen are honeybees. If you do not see 3 to 4 honeybees per tree visiting the flowers your fruit set may be less than desired.

    A fourth reason fruit trees don’t bear fruit is the effect from last year's crop. Fruit trees form their flowers the previous growing season. Heavy crops the previous year can reduce flower formation for the next year by reducing growth or preventing flower formation. To avoid this, remove some of the fruit within 2 to 4 weeks after bloom. With apples and pears, thin the fruit down to one per cluster and allow only fruit bearing clusters every 6 to 10 inches.

    Other reasons for poor fruiting include tree age, competition for nutrients between developing fruit and vegetative growth, inadequate sun exposure, and pests/diseases. An important consideration is the maturity of the tree. If trees are bought at 1 or 2 years old, it’s likely to be another 2 or 3 years before you can expect a reasonable harvest unless the tree is on dwarf rootstocks which are less likely to suffer a delay in coming into bearing. Also of note is biennial bearing which is a problem in some fruit trees, particularly apples and pears, where they crop heavily in one year and then produce little or nothing the next.

    Frequently there is no single reason for a lack of a fruit crop but rather a combination of all the above reasons. The goal of the home orchardist is to try and control as many of these causes as possible.