Why do my orange trees have no fruit? Blame pruning, watering

I have two orange trees that were planted 12 years ago. They bore beautiful fruit until four years ago, when my gardener pruned them rather severely. Since that pruning, no more fruit at all. But the trees appear healthy -- very green, with few yellowing leaves. Please advise as to how we can get them to bear fruit again.

Frances Berlin

Palm Desert

For answers on if or how gardeners can revive a badly pruned citrus tree, we turned to Frank McDonough, botanist at the Los Angeles County Arboretum and Botanic Garden in Arcadia.

McDonough’s first step was to ask Berlin more questions: How do you fertilize your trees? What type of fertilizer, how much and how many times per year? How frequently do you water your tree, and for how many minutes? How many hours of direct sun do these trees receive?

With more information in hand, McDonough offered this response to Berlin:

From what you’ve told me, I am surprised your citrus are still alive. Irrigating citrus three times a day is more than unnecessary. It’s highly deleterious. Waterlogged soil causes citrus blooms and leaves to fall off of the tree; no blooms mean no fruit. Soil watered that frequently also is ideal for the root rot organism known as Phytophthora.

How often should you water citrus? Once the trees have been established, they should be irrigated no more than once a week, ideally once every two weeks.

But over-watering is not the only problem here. The kind of severe trimming that your trees received on a regular basis makes them susceptible to sunburn that can kill branches and burn trunks, over time depleting the energy that is stored underneath the bark of the tree -- energy that is needed to produce new leaves and fruit.

Citrus trees should be pruned back by no more than one-quarter the volume of their canopy, and they should be pruned only if they are getting too tall to harvest the fruit easily.

With the constant pruning and watering, your trees may not be salvageable. I would replace them and start over, with these hints in mind:

• When you’re planting a new citrus tree, dig the hole three times wider and just as deep as the container -- no deeper. Do not use any planting mix in the hole.
• Once you’ve finished planting the tree, create a watering basin consisting of two concentric circular soil berms, both 6 inches tall. One berm should be 6 inches from the trunk, and the other should be 3 feet from the trunk. Use soil dug from the planting hole to do this.
• Fill the watering basin two times a week for the first six months, then once a week for the six months after that. That should help the tree to get established, and for about two years you can reduce the watering frequency to about once every two weeks.
• Do not fertilize the tree until it has been in the ground for at least a year
• Do not trim the tree for at least three years, preferably five, after planting.

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