(News article for June 12, 2020)

Last week’s article addressed reasons that vegetable plants sometimes fail to fruit. This week, I’ll talk about reasons for a lack of production in fruit and nut crops.

One reason that fruit plants don’t produce is improper pruning.

In a number of fruit crops, having fruit depends on having year-old wood. Blueberries, muscadines, and peaches are examples. If these plants are pruned in a way that removes all growth from the previous season, the plant will not flower and thus will not produce fruit.

This is why we suggest pruning blueberries for height, if needed, shortly after harvest. Here in Louisiana, this gives plants time to produce new growth and for that growth to set flower buds for the following year.

Blackberries have a perennial roots system and can live for a number of years, but individual canes only live for two years. On traditional varieties (new primocane-fruiting varieties are exceptions), a cane arises in the first year, overwinters, and produces fruit in the second year. If the cane is removed before the second season, it will not fruit.

Another reason that fruit or nut plants might not produce is because of a lack of appropriate pollination. Some plants need cross-pollination by a different variety.

Muscadine vines have either perfect flowers (ones with both male and female parts), female flowers only, or male flowers only. No cultivated varieties have only male flowers, but some wild vines do.

If you have a female-only variety, such as ‘Supreme’, ‘Summit’, ‘Fry’, or ‘Scuppernong’, you’ll need either a perfect-flowered (self-fertile) variety or a wild male vine nearby to provide pollen. If you only have room for one vine, be sure to get a self-fertile variety.

In some crops, self-incompatibility is the issue. Flowers of blueberries and apple plants, for example, have both male and female parts, but the plants typically need pollen from another variety to produce a full crop.

Pecans exemplify another case in which cross-pollination is needed. On pecans of some varieties, the male flowers shed pollen before the female flowers are receptive to it. These are called Type I, or protandrous. In other varieties, the female flowers are receptive before the male flowers shed pollen. These are Type II, or protogynous.

In reality, there is quite a bit of variation among pecan varieties with respect to how much, if any, the periods of pollen shedding and pistil (female flower part) receptivity overlap. In some varieties, the pollen shedding and pistil receptivity periods overlap quite a bit. In others, they don’t overlap at all. In general, it’s recommended that at least one Type I and one Type II pecan variety be planted.

Sometimes, a pecan tree in another person’s yard or in the woods will provide pollen. The pollen source needs to be within one-quarter of a mile, and closer is better.

Weather can contribute to plants not producing. Late freezes sometimes kill the flowers of early-flowering crops like blueberries and peaches.

Varieties with a chilling requirement too low for the area are more likely to bloom too early and have flowers killed by late freezes. On the other hand, one with a chilling requirement that is too great will bloom sporadically or not at all. So, choose varieties compatible with the number of chilling hours your area receives.

Some crops tend to alternate bear, or produce few fruit or nuts in a year after they produce a lot. Pecans are notorious for this, and some varieties are more prone to it than others. It’s sometimes seen in citrus, as well.

Finally, some plants are just too young to produce a full crop. If you grow a pecan tree from seed, it may take ten to fifteen years to produce nuts. Circumventing this juvenile stage is one reason that pecan trees are often grafted. Grafted pecans of some varieties may bear in as few as five years, although some take as long as ten.

There are also fertility issues, environmental stressors, insects, and diseases that can affect fruit and nut production, but the above are some general reasons fruit or nut trees may fail to produce, or produce less than expected.

Let me know if you have questions.

Contact Mary Helen Ferguson.

'Supreme' is an example of a female-flowered muscadine variety. To get fruit production, either a perfect-flowered variety or a wild male-flowered vine must be nearby to provide pollen. (Photo by D. Nance, USDA Agricultural Research Service)