Experts tackle readers’ garden questions.
Q: We have had a dwarf navel orange tree growing in a half wine barrel for over 15 years with no problems. All of a sudden, all the green leaves are falling off and the tree is almost bare. All the oranges fell off, too. Could it be too much rain? The soil does not look like it is sitting in a lot of water and there are no bugs or insects on the leaves. We missed covering it a few times when it was really cold, and the leaves looked a bit wilted and brown. Will it grow back new leaves or is the tree gone?
Betty Romeo, Fair Oaks
Master gardener Rachel Tooker: Because citrus is an evergreen, leaf drop is common, even in healthy trees. Citrus trees typically shed leaves after spring bloom and again in the fall. Old leaves will drop as the tree produces new leaves. If the canopy does not appear to be thinning, there is little cause for alarm.
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However, in a case like yours, where the tree is almost bare, there is definitely an indication of trouble.
Rapid leaf loss can be symptomatic of a variety of issues, including over- or under-watering, weather injury (frost, wind, sun), fungal and viral diseases, pesticide damage, insect damage (scale, mites, whitefly, etc.) and other problems.
If the citrus has not been repotted in 15 years, the drainage holes may no longer be functioning, causing the tree to become waterlogged. The tree also may have been given too much or too little fertilizer, making it more susceptible to environmental issues.
Because the tree was unprotected a few times during extreme cold spells, freezing temperatures and rainy weather are the most likely culprits. The leaves looking a bit wilted and brown is another good indication of frost damage. Late fall fertilizing promotes tender new leaves that are more susceptible to freezing.
In general, if freeze injury is not too extensive, leaves on the tree can recover, sometimes with some discoloration. However, seriously frozen leaves will remain on the tree for several weeks before dropping off. With more extensive freezing, twigs and branches can also be affected. This can be diagnosed by wood discoloration, dead patches on the branches or bark, or bark splitting.
If twigs and branches have not been too severely damaged, the leaves fall off more rapidly, which can be a good sign that the tree will recover.
It can take several months to a year before you understand the full extent of freeze injury. In all cases, it is best to move slowly and allow the tree to begin healing on its own before taking corrective action. For instance, early pruned trees recover more slowly than trees pruned later.
Premature pruning may cause further dieback, and some limbs that could have recovered on their own might be removed unnecessarily. Move slowly, wait until at least midsummer to understand the extent of frost injury, and then begin to prune and rebuild the structure of the tree as needed.
The lack of leaves requires other considerations as the tree recovers. The trunk of the tree will be more susceptible to sunburn. Protect the trunk and large limbs facing south and southwest on the tree by painting with a 1-to-1 mixture of light-colored latex paint and water. Sunburned wood will blister and crack, allowing disease and insects to enter and cause more damage.
In addition, because of the extent of leaf loss, the tree will need less water until a new crop of leaves develops. Irrigate only when soil conditions indicate a need. Examine the soil by digging down several inches (toward the edge of the container) or use a moisture meter.
Lastly, be cautious about applying fertilizer. If the tree is only slightly damaged, you can follow normal fertilization practices. In containers, small, regular doses of an organic, slow-release fertilizer from spring through fall will help to maintain nutrients that are washed out of the container through irrigation. However, if the tree has more damage, your regular fertilization schedule may actually cause excess sucker growth until the correct proportion of roots to canopy is re-established. Wait until the canopy takes shape before resuming a regular fertilization schedule.
In addition to frost damage, winter rains may also have caused leaf drop. While the top of the barrel may not appear wet, it may be soggier toward the base. Tip the wine barrel on its side to check the drainage holes. Elevating the barrel on blocks or bricks will allow you to monitor the drainage and promote good air circulation going forward.
Over the ensuing months, watch for insect damage or indications of fungal or viral diseases, including gumming or sap on branches, yellowing leaves, poor fruit development, mushrooms at the base of the tree, or darker and decaying roots, as the tree will be stressed for a while before it recovers.
For more information on growing citrus in the Sacramento area, check out the Home Orchard webpage on the UC Master Gardeners of Sacramento County website at http://sacmg.ucanr.edu/Fruit_and_nuts.
Rachel Tooker is a UC Cooperative Extension master gardener for Sacramento County.
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