Our last newsletter may have prompted you to have more questions about citrus. The good news is, the topic for January Classes at Stanislaus County Libraries is (you guessed it) Growing Citrus Trees! We hope to see you at one of these free classes.
You can also see a list of our classes on our calendar by visiting our website at https://ucanr.edu/sites/stancountymg/Calendar/
p.s. February's topic is Spring Vegetable Gardening, stay tuned for more information!
- Author: Anne Schellman
- Author: Ed Perry
- Why are the leaves on my orange tree turning yellow?
It's common for citrus tree leaves to turn yellow in winter*. Fertilize to provide the tree with nutrients now, then watch as leaves green up in spring. Avoid fertilizing in fall, which encourages new growth favored by pest and can leave the tree susceptible to frost injury.
- How do I know if my oranges are ripe/when should I pick my oranges?
You don't have to pick all your oranges once they ripen. In fact, the best place to store oranges is on the tree, where they stay fresh! Pick as needed, unless temperatures below 28 F are predicted, then you'll want to harvest.
- What is this pest?
Scales and whiteflies suck plant juices and weaken the plant. Ants do two things:
- Protect pests from predators like ladybugs, parasitic wasps (very tiny wasps) and lacewings.
- “Harvest” honeydew (a sticky sugary substance excreted by these pests) for food, in a symbiotic relationship that does not include the gardener.
- Why are my oranges splitting?
The reason this happens is not well understood, although it's often related to changes in weather conditions. However, allowing the soil to dry out too much between irrigations is believed to result in increased splitting. Make sure your tree has a constant supply of moisture by watering monthly during the dry season.
- When should I prune my orange tree?
When pruning deciduous trees like peach, plum or cherry, after leaf drop, don't be tempted to prune citrus! Citrus trees are evergreen and require little if any pruning except to control size. If you'd like to keep a new citrus tree under 5 feet tall, you can carefully prune it in spring to manage the height. This way, you won't need a ladder to pick fruit again!
Avoid pruning in fall or winter, which encourages new growth favored by pests and can leave the tree susceptible to frost injury.
*if your tree leaves turn yellow and it's not winter, this may be a different problem.
- Author: Ed Perry
For many in California, the backyard orange or grapefruit tree is almost a member of the family, and any negative change in its appearance elicits concern. One such change in appearance is leaf yellowing and drop that often occurs during the winter in citrus. Citrus leaves can remain on the tree for as long as three years depending on tree vigor, but disease, inadequate or excessive nitrogen fertility, excessive salt or born in the soil, poor irrigation practices, freezing temperatures, pest pressures and low light levels significantly reduce leaf longevity. Excessive leaf drop during the growing season is more likely to indicate a serious problem than leaf drop during the winter. Winter leaf drop normally reflects nothing more than a momentary swing in the natural balance between the natural elimination of old senescing leaves and their replacement.
Reduce winter water applications to citrus trees that have defoliated or that have a significantly thinning canopy. Trees like this require little, if any, supplemental irrigation. Even a mature tree with a full leaf canopy will require less than 10% of the water that it would require during the summer.
The best indicator of tree health for a defoliating citrus tree during the winter will be how well it produces the first flush of new growth in the spring. A decision to keep or remove a citrus tree based on tree health should not be made during the winter. Even trees that lose most of their leaves during winter are capable of replacing leaf canopies with the spring flush of growth, usually with little loss in fruit production. Trees that do not produce a vigorous flush in early spring may have a more serious problem. March is an excellent month to begin applying fertilizer to encourage new leaf growth and fruit production and to help keep an old friend of the farm or family backyard around for years to come.
Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.
Here are the resources mentioned during the talk.
Citrus varieties
https://citrusvariety.ucr.edu/citrus-varieties
UC IPM website https://ipm.ucanr.edu/PMG/menu.homegarden.html
Ants
https://ipm.ucanr.edu/PMG/PESTNOTES/pn7411.html
Selected Citrus Varieties for the Home Gardener https://anrcatalog.ucanr.edu/pdf/8472.pdf
Grafting and Budding Citrus and Avocados in the Home Garden
https://anrcatalog.ucanr.edu/pdf/8001.pdf
Forestierre Underground Gardens in Fresno, CA
https://undergroundgardens.com/
- Author: Anne Schellman
What is a Deciduous Fruit tree?
Deciduous fruit trees lose their leaves in fall, and include apple, pear, fig, pomegranate, nectarine, cherry, apricot, peach, and plum.
Planting New Trees & Understanding Where Fruit Originates
Sometimes a fruit tree mysteriously dies, and the gardener isn't sure what happened. A common cause is a tree that was planted too deeply. Root and crown rot slowly affect the tree, causing it to die years later. Watch the detailed instructions on how to plant correctly.
It's important to understand how new fruit develops and grows on the tree. Not all deciduous fruit trees produce fruit in the same place. It's important to know this so you don't accidentally cut off fruit spurs and damage your tree's ability to produce fruit. See this video for guidance. https://www.youtube.com/watch?v=-4fgVrf8XHE&t=250s
Publication - Fruit Trees: Planting and Care of Young Trees https://anrcatalog.ucanr.edu/Details.aspx?itemNo=8048
Fruit Trees: Training and Pruning Deciduous Trees https://anrcatalog.ucanr.edu/Details.aspx?itemNo=8057
Keeping New Trees Small – the Fruit Bush Method
Tired of out-of-control fruit trees? If you are planting a new tree, watch this video! It details the Fruit Bush Method, a specific way of keeping fruit trees small. See photos of 5-6' tall fruit trees planted over 30 years ago that continue to produce an ample amount of fruit. https://www.youtube.com/watch?v=ry4YAp6NzdI&t=1s
Pruning Established Trees
Other Helpful Publications
Fruit Trees: Thinning Young Fruit https://anrcatalog.ucanr.edu/Details.aspx?itemNo=8047
What about Citrus Trees?
Citrus trees such as oranges, lemons, grapefruits, lime, and kumquats are evergreen trees and need different care than deciduous trees. It's not recommended to prune citrus trees at the same time as deciduous fruit trees. Wait until spring to prune your tree for size and shape.
We are offering an online class on citrus on January 31, so watch for our registration advertisement in about a week. Locally, we will be teaching at 8 library locations about citrus during March.
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