Signs of autumn are all around us. . .we've had some rain, trees are showing off their fall colors and losing their leaves, fewer plants are blooming, the days have gotten shorter with the nights getting chillier. While nature has its own way of coping with the colder winter months, there are plants in our gardens that can be sensitive to freezing temperatures. Citrus, succulents, perennials, young plants that recently went into the ground, and many tropical and subtropical plants can be vulnerable. But there are a few things you can do to help protect your garden during potential freezing spells.

Mulching Perennials

Perennials return year after year. Hardy ones will need little, if any, assistance to get through the cold months, but some may need protection. Mulching helps even the soil temperature, preventing the ground from freezing when the temperatures drop below 32°F/0°C. A layer of 2-3 inches is best. A deciduous plant's own dead leaves can help protect its crown and roots from the cold, so leave the leaves until next spring, adding more mulch as needed. Other sources of mulch include bark, straw, shredded branches, and compost.  

Trees and Shrubs

Trees and shrubs usually have an easier time getting through the winter if they are in good shape. However, if a freeze is forecasted, one of the most important things to do is to ensure they have been watered 2-3 days prior, especially if autumn has been dry. As with perennials, mulching with fallen leaves or other mulch will help protect the roots, but do not have mulch up against the tree trunk or plant stem, which could cause rot to occur.  

Wrapping trunks of young trees with blankets, towels or piping insulation will provide added protection.

Bulbs

Fall is the time to plant hardy spring-blooming bulbs, but some bulbs such as gladiolus, cannas and dahlias are sensitive to winter cold, and may not survive. You may wish to dig these up and store them over the winter.

Wait until after the first frost, then gently dig up the bulbs or tubers. Cut away any leaves and brush off as much soil as possible. Let them dry out in a cool spot for about a week. Label them so you'll remember what they are!  Pack them in a breathable box, such as a cardboard box, storing the bulbs so they don't touch each other, and cover them in sawdust or shredded newspapers. Keep them in a cool, dark location that is below 45°F, but doesn't freeze.

Citrus

Different types of citruses have different cold hardiness. The leaves, green wood and fruit are more frost sensitive than hard wood. Mandarins and kumquats are the most tolerant of cold, with oranges, lemons and limes being less tolerant. However, if a cold snap has colder than usual temperatures and/or lasts more than a short period, even mandarins and kumquats can suffer. Any ripe fruit should be removed prior to freezing temperatures.

Citrus plants can be protected by frost cloths which allow some light and air to penetrate and can stay on plants for a few days at a time. They can also lay directly on plant foliage. If you use other type of cloth such as burlap or cotton sheets, use stakes to hold the cloth away from the plant greenery. Remove it during daytime when temperatures are above freezing and sunny, and replace it each night prior to sunset. Whatever cloth you use, make sure the cloth goes all the way to the ground to capture radiant heat from the ground. If there is mulch around the plant, rake away during the day, if above freezing and sunny, to allow the soil to warm up. 

Roses

Some roses are more sensitive to cold than others. As a group, hybrid tea roses are the most vulnerable. Make sure they are watered prior to predicted freezing temperatures, protect the root zone with mulch on the soil mound. You may also wish to cover your sensitive roses with frost cloths.

Container Plants

As always, water the plant a few days prior to an expected freeze. Ideally, if you are able to pull plants in pots into the garage, shed, or other enclosed area, do so.  While not as effective as an enclosed area, moving container plants onto a patio, or up against the side of the house or garage, preferably beneath an overhang will provide some protection. If unable to move the container, you can cover them up with frost cloth as discussed in the citrus section.

What do do if frost damages your plants? Wait!

Frost damage occurs when the water inside the cells of a plant freeze, causing damage to the cellular walls, which harms the overall health of the plant. Frost damaged vegetation will wilt, turning brown or black, as if they have been scorched. The bark may crack, or split. In severe or prolonged periods of frost the plant can die.

If you see what appears to be frost damage, wait until late spring until all chance of frost has passed. Plants are resilient and can often recover on its own, producing new growth.  Pruning what seems to be damaged branches too soon can cause significantly more trauma, even death, to a vulnerable plant that might otherwise have recovered in the spring. 

Resources

• https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=22929
• https://sacmg.ucanr.edu/Frost_Protection/
• https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=45517
• http://ipm.ucanr.edu/PMG/GARDEN/ENVIRON/frostdamage.html

Denise Godbout-Avant has been a UC Cooperative Extension Master Gardener in Stanislaus County since 2020.

Pruning is a difficult topic to discuss and describe and to arrive at a consistent approach from year to year.

And now Simon Newett, Bridie Carr and Renata Grunennvaldt have put together a survey of what avocado growers worldwide are doing to control vegetative growth.  The survey was conducted through an avocado industry extension project funded by Australian grower levies, Hort Innovation Ltd (Australia) and the Queensland governments (Hort Innovation Limited & DAF).  Thank them for their efforts.

Obviously the methods and results reported in the survey will vary according to the characteristics of the orchard and the environment in which the trees are grown.  And whether a plant growth regulator is used, such as uniconazole or propiconazole, to retard growth.

The most interesting findings were the popularity of selective limb removal, the younger tree age in which pruning is now commenced, the smaller tree size being aimed for and the fact that most people try to remove about 20% of the canopy each year.

Check out what other growers are doing in their orchards by clicking on the link at the bottom of the page.

The UC Davis Bee Haven, part of the Department of Entomology and Nematology, will host two fall hybrid (online and in-person) courses: "I Planted a Bee Garden: Now What?" and "Pruning the Bee Garden."

Christine Casey, academic program management officer of the Bee Haven, will teach the classes. The $50 registration fee for each class covers a light breakfast and course materials. Proceeds will support the operation of The Haven.

The first class, on "I Planted a Bee Garden," will take place Saturday, Oct. 29 from 9 a.m. to 10:30 a.m. in the Bee Haven, located on Bee Biology Road, next to the Harry H. Laidlaw Jr. Honey Bee Research Facility. Topics will cover turf removal and weed control, best bee plants for new gardeners, and turf vs. bee garden maintenance. Enrollment is limited to 25.  To register, access
http://registration.ucdavis.edu/Item/Details/870.

The second class, "Pruning the Bee Garden," will be from 9 a.m. to 11 a.m., Saturday, Nov. 5. "Bee gardens are all about flowers, and pruning The Haven's plants is an essential part of creating ample flowers for our bees," Casey said. Topics will include pruning techniques and strategies for many plant types; the science and biology of pruning; and practice pruning techniques in The Haven. To register, access
https://registration.ucdavis.edu/Item/Details/871.

UC Extension apiculturist Elina Lastro Niño of the Department of Entomology and Nematology serves the faculty director of the half-acre garden, planted in the fall of 2019 under the direction of interim department chair Lynn Kimsey, director of the Bohart Museum of Entomology. Häagen-Dazs was the primary donor. (See timeline and history of the garden.)

The garden features art projects by the UC Davis Art/Science Fusion Program, co-founded and co-directed by the duo of entomologist/artist Diane Ullman, professor and former chair of the UC Davis Department of Entomology, and self-described "rock artist" Donna Billick of Davis. A 200-pound ceramic-mosaic bee sculpture, Miss Bee Haven by Billick anchors the garden.

The Haven is open daily from dawn to dusk. Admission is free. For more information access the website,  Facebook page, Casey's Bee Gardener blog on the UC Agriculture and Natural Resources website, the Instagram account or the Twitter account. 

Prune Apricot and Cherry Trees in August

If you have apricot, cherry, or related hybrid tree varieties such as aprium and pluot in your yard, plan to prune them before the end of August. This timing will help prevent infection by a deadly fungal disease called Eutypa Dieback that can kill these trees as well as grape vines.

When infected by Eutypa, branches or entire trees wilt and die suddenly, often with the leaves still attached.

Apricot tree with branch killed by Eutypa

 

Signs that your tree may be infected by Eutypa include darkly discolored cankers on the branches and oozing of amber colored gummy sap.

Eutypa cankers on apricot branch

 

Oozing Sap on Cherry Tree from Eutypa Infection

[Editorial Note: apricot photos downloaded from UC Repository. Cherry tree photocopied from UC ANR blog article by Chuck Ingels, UCCE Sacramento, https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=16014 ]

Many other varieties of trees and shrubs can become infected with the Eutypa fungus without showing disease symptoms or progressing to the dieback stage. These other tree and shrub varieties can serve as store houses for the Eutypa pathogens that could potentially spread to your grape vines and apricot, cherry, aprium and pluot trees. Trees and shrubs that can serve as reservoirs for the disease include almond, apple, blueberry, crabapple, honeysuckle, kiwi, oleander, pear, and certain native plants such as big leaf maple, California buckeye, ceanothus, and willow.

Eutypa disease is spread from an infected tree, shrub or vine to uninfected trees by splashing water from sprinklers or rain. The splashing water allows the fungal spores to enter through pruning or other wounds. Pruning vulnerable tree varieties by the end of August allows pruning wounds to heal and close before the typical start of the rainy season in Contra Costa County in late October. Also, avoid using sprinklers near recently pruned trees since water from sprinklers can also spread infections. Using these precautions will reduce the risk of infection for your trees.

Studies have shown that the Eutypa pathogens can also be spread on pruning tools that have been used to prune infected trees and shrubs. To prevent such transmission, be sure to disinfect your pruning tools before and after pruning.

To disinfect tools, soak them for thirty minutes in a 10% bleach solution (nine parts water to one part bleach). Bleach is corrosive so be sure to rinse the tools thoroughly with water after soaking. Then oil them. The bleach solution loses 50% of its effectiveness after two hours, so be sure to use a freshly mixed batch.

As an alternative to bleach, you can disinfect pruning tools with 70% isopropyl alcohol. Just spray it on your tools and it will kill any pathogens almost immediately. Alcohol is not corrosive, so you don't need to rinse it off tools.

An internet search for “how to prune apricot [or cherry, aprium or pluot] trees” will help you find videos that demonstrate good pruning techniques. Just be aware that most pruning videos are filmed when the trees are dormant. With no leaves, the branches can be more easily shown in the video to demonstrate pruning techniques. In California, you don't want to wait until the dormant season to prune these vulnerable trees because that increases the risk of an Eutypa infection. So, you'll need to adapt the pruning techniques to a tree that still has leaves.

For more information on Eutypa disease, visit this University of California IPM website: http://ipm.ucanr.edu/PMG/GARDEN/FRUIT/DISEASE/eutypadieback.html