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: Anne Schellman
- Editor: Roger A Duncan
Want fall color in your landscape next year?
Read about the trees you've noticed around town that are currently “popping” with color. And, if you plant a tree now (or in early spring), you can have fall color in your landscape next year! Here are some excellent tree species to choose from that thrive in our area (USDA Zone 9b):
Chinese Pistache – Pistachia chinensis
The Chinese pistache is Ed Perry's favorite tree. Ed was the Environmental Horticulture Advisor for over 35 years at UC Cooperative Extension in Stanislaus County. He chose this tree not only for its fall color, but because it produces good shade and has “well-behaved” roots. Opt for the male cultivar ‘Keith Davey.' Female cultivars have colorful berries which although pretty, are considered messy and not suitable for over a patio.
Height: 30-50'
Light needs: Plant in full sun.
Water needs: Moderate. Does well in lawns.
Note: You can't go wrong with this tree! Also, it is not closely related to the nut bearing pistachio tree.
Maple Trees – Acer rubrum
Light needs: Plant in full sun or partial shade.
Height: 40-50'
Water needs: Regular water. Does well in lawns, but water separately from the lawn.
Note: Sprinkler water will not be enough for this tree.
Bradford Flowering Pear – Prunus calleryana ‘Bradford'
This flowering pear has cheerful white blooms in spring and produce fall color during cool winters. Their roots are well-behaved so they can be planted near sidewalk. Please note, many cultivars of flowering pear have problems such as mistletoe and fireblight. Make sure you choose a Bradford pear. After bloom, this tree does drop small fruits that are messy.
Height: 40-50'
Light needs: Plant in full sun.
Water needs: Moderate. Does well in lawns.
Note: although bred to be fruitless, the Bradford pear cross pollinates with other pears which is why it produces inedible “fruit.”
Japanese Maple Trees – Acer palmatum
Light needs: Plant in partial shade, some species (‘Emperor One') are adapted to full sun.
Height: 6-20', varies. Do some research before choosing your tree.
Water needs: Regular water.
Note: This tree can give year-round interest!
Ginkgo – Ginkgo biloba
This ancient tree existed long before dinosaurs roamed the earth. In fact, fossils of gingko leaves have been discovered from the Jurassic period! Ginkgo trees leaves turn a beautiful golden color in fall. Choose a male cultivar such as ‘Saratoga' or ‘Autumn Gold.' Female cultivars produce fruit that some people consider unpleasant.
Light needs: Plant in full sun.
Height: 30-50.'
Water needs: Moderate water; can tolerate drought but won't look healthy.
Note: Excellent street or patio tree, also does well in a lawn.
Liquidambar – Liquidambar styraciflua
Light needs: Plant in full sun.
Height: 50-60.'
Water needs: Regular water.
Note: Surface roots can crack sidewalks and come up in lawns.
Tree Notes – Choosing a Tree
When choosing a tree, look for one with leaves growing along the entire stem. Avoid trees that resemble a mature tree (with a long stem and a heavy top). The leaves are necessary to help the tree develop a strong trunk.
Tree Notes – Planting
Planting a tree correctly is essential to having a healthy tree. Follow these steps:
Step 1: Remove the tree stake.
Step 2: Dig a hole twice as wide but the same depth as the container.
Step 3: After removing the “root ball” (area of soil and roots) from the container, set it in the hole.
Step 4: Make sure the top of the root ball is lined up with the surrounding soil or a little higher.
Step 5: Fill in around the root ball with removed soil, do not cover over the root ball with soil. Make sure the root ball is still showing and is level with the ground.
Step 6: Create a basin around the base of the tree and water well.
Tree Notes – Staking
If you remove the stake from your new tree and it falls over, return the tree. Healthy trees should not fall over and do not need to be staked. In fact, a tree that can't stand upright that grows into a mature tree is likely to become a landscape hazard** in the future.
Allowing your new tree to sway with the wind helps it develop a strong trunk and root system. The only time it is recommended to stake trees is in areas with heavy wind. In this case, two stakes should be used, and then removed after one year. Learn more about tree staking in the Planting Landscape Trees publication below.
Tree Notes – Water
All newly planted trees need regular water for the first 2-5 years after planting. Regular water means keeping the soil moist but not too wet or allowing it to dry out. Once their roots are established, trees need deep water once or twice per month during the dry season (May-October), depending on temperature, tree species, soil type, and other factors.
Resources
Stanislaus County Tree Guide
Looking for more tree recommendations? Visit our publications page and scroll to the bottom of the page to click on our “Trees in Your Home Garden” publication at https://cestanislaus.ucanr.edu/Gardening_Publications/
Planting Landscape Trees
https://anrcatalog.ucanr.edu/pdf/8046.pdf
*University research has shown that adding amendments such as compost and fertilizer to planting holes does not help trees; in fact, it can cause problem. Read more at https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=46215
**worried you may have a hazardous tree in your landscape? Download this free guide for tips on how to inspect it. https://anrcatalog.ucanr.edu/pdf/8365.pdf
/h3>/h3>/h3>/h3>/h3>/h3>/h3>/h3>/h3>/h3>/h3>/h4>- Author: Elinor Teague
Last season's torrential winter rains provided a much-needed relief from 20 years of drought. However, Central Valley home gardeners deal with the effects of drought every summer because, even with regular irrigation, extremely high temperatures during our long, rainless summers create drought stress conditions.
Large mature shade-producing landscape trees and bushes have been weakened by years of drought. Summer drought speeds up the normal fall process of slowing vegetative growth and also leads to smaller leaves and early leaf drop on deciduous plants. Leaves make food for trees. Trees and bushes with fewer, smaller leaves in fall have fewer stored resources and less food for next year's growth. Small, fine roots die and plants are unable to draw up and store enough water and nutrients to overwinter well and to quickly regain their vigor in spring.
Check soil moisture levels now in several places underneath large tree and bush canopies, especially those that have not received at least monthly deep irrigation during the summer months. The top few inches of soil near trees and bushes in lawn areas may be moist from sprinkler water. Sprinkler water generally only penetrates to a depth of four inches, but try to check moisture levels at least 12 inches deep using a shovel or trowel.
Deep irrigate large, mature landscape trees and bushes in early fall to a depth of 18 inches before dormancy to help them better tolerate cold or below freezing temperatures. Continue to provide monthly slow deep irrigation throughout the winter months unless rainfall from atmospheric rivers provides sufficient water to soak the soil.
Wet soil around the roots provides better insulation against cold temperatures than dry soil. During the next few weeks closely examine your and your neighbors' large trees and bushes for branch dieback to prevent damage from falling dead branches during winter storms. Winter pruning of deciduous trees and bushes should wait until after leaf fall, but dead wood can be removed at any time.
If dead branches are large or higher than 15 feet it's best to hire a certified arborist to do the work. Many large landscape trees were blown over during last year's violent windstorms. Root systems of surviving trees may have been compromised or broken from the soil from high winds. Changes in the angle of the tree trunk as it begins to tip may not be obvious.
Check the soil under canopies for evidence of root uprise with special attention to the northwest and western sides; our winter storm winds generally come from the northwest or western direction. If you see signs of tree tipping consult a certified arborist who can determine whether the tree is unsafe and should be removed before the winter storms.
Newly planted trees and large bushes should be properly staked to help them stand up to strong winds. Use strong poles and cushioned ties on the trunk and position the poles or stakes at the edge of the rootball on the northwest or west side. Most trees and bushes have a heavier side with more or bigger branches. Check that the heaviest side of the tree or bush is planted to back up to the northwest or west. Replant if necessary to correctly balance the new tree against the force of winter winds.
- Author: Janet Hartin
Welcome to Fall!
It's my favorite season and likely for many of you, as well. Beyond the holidays and extra time with family and friends, nature radiates its beautiful hues. In addition to lovely foliage, deciduous trees often expose exquisitely shaped and sturdy trunks. And, of course, there is the lovely fall foliage showcased by many species.
Did you ever wonder why trees "turn" color in the fall? The short answer: It's primarily a function of long, cool fall nights and short, sunny days. The longer answer? Chlorophyll is responsible for the basic green color of leaves we see in spring and summer and is a necessary component of photosynthesis, which uses sunlight to manufacture sugar (food) that is stored during the dormant period of the year. Carotenoids produce yellow, orange and even brown pigments in crops such as carrots, squash, bananas and many ornamental plants such as daffodils and poppies. Anthocyanins are red and orange in color and are most linked to lavish displays of brilliant fall foliage. They also give rise to coloring of strawberries, plums and cherries.
Here's the kicker: While chlorophyll and carotenoids are present in leaf cell chloroplasts throughout the entire growing season, during fall chlorophyll begins to break down. Voila! The lovely yellow and orange hues we all look forward to seeing are finally exposed. In addition, red hues (called anthocyanins) are produced in fall. So, in reality foliage doesn't "turn" orange or red at all.
Interestingly, the actual timing of color change varies across species and appears to be genetically inherited. The same species will exhibit a similar color scheme in cool temperatures in higher elevations at nearly the same time as it does in warmer lower elevation climates.
The intensity of color can vary quite a bit however. Where do temperatures enter the picture? Both the amount of color and the overall intensity of fall color is very linked to weather conditions that occur prior to and during the actual time the chlorophyll in leaves winds down. The most brilliant displays occur after several warm, sunny days and cool, crisp (above freezing) nights. This is because although lots of sugars are made in leaves during sunny daytime hours, the corresponding cool nights prevent the sugars from moving out. The amount of soil moisture also helps ensure that from year to year fall colors vary even in the same trees. So, either a late spring or a prolonged drought can both delay the display of fall color by a few days or even a few weeks.
What's the recipe for the most brilliant fall display? Most likely a warm, moist spring followed by a warm summer and sunny fall with cool autumn nights. Although fall color is not nearly as spectacular in lower elevations of Southern California compared to other colder areas of the nation, the liquidambar or American sweet gum (Liquidambar styraciflua) offers some pretty impressive fall color and an impressive 300 to 400-year life span. (Did you know that liquidambar got its name because it at one time was a sought-after chewing gum for Native Americans?)
Two “climate-ready” tree species with lovely fall foliage that grow in both the west portion of the county and the desert are the ‘Keith Davey' Pistache, a large street and park tree sporting crimson to scarlet colored foliage and its relative, the ‘Red Push' Pistache, a hybrid between P. atlántica x P. integerrima) which has lovely red foliage as it emerges in Spring as well as Fall. Others include the Raywood Ash (Fraxinus oxycarpa 'Raywood') sporting a reddish-purple hue in the fall, and the ‘Sunburst' Locust (Gleditsia triacanthos var. inermis 'Sunburst') which offers a vivid display of fall color. Unfortunately, it is susceptible to the Invasive Shot-Hole Borer. If you have one of these lovely trees already, take good care of it to help it stand up to this aggressive pest!
Happy Fall! Enjoy the cooler weather, family and friends, and lovely trees!