Autumn is the favorite season for many people. The days are shorter, the weather cooler, the bright blue skies of summer fade to a softer blue with clouds, and the leaves of some trees start presenting their autumn glory. 

Why do some trees change color and drop their leaves before winter?  And why are there different colors?

Leaves are colored by pigment molecules. Most leaves appear green because they contain an abundance of the pigment chlorophyll. Chlorophyll is the site of photosynthesis where the sun's energy is converted into the carbohydrates that are plants' food source. During the cold winter months when there is less sunlight, it would take too much energy for some trees to keep their leaves healthy. So deciduous trees lose their leaves for the winter. Evergreen trees have a different strategy for dealing with winter's challenges (which is a topic for another time!).

Temperature, precipitation, and soil moisture are all factors which contribute to plants dropping their leaves in autumn, but the primary agent is light, or rather, the lack of it. After the autumn equinox, the shorter days with longer nights triggers chemical changes, causing the tree to seal off vessels that supply the leaves with nutrients and water. The combination of reduced light, lack of nutrients, and less water starts the process of the green chlorophyll to break down. As the green fades, the other pigments in the leaves, which were present all along, but were masked by the green chlorophyll, begin to reveal other bright pigments. In time the leaf is blown off from the sealed cut, or falls from its own weight. 

Leaves containing primarily anthocyanin pigments will appear red. Carotenoids can be orange, yellow or red. Xanthophylls are yellow-brown. Some leaves, like oaks, contain tannins which will produce brownish colors. A chemical process called paper chromatography of a plant extract will separate the various pigments present which can reveal some of the pigments found in leaves. This photo illustrates pigments found in mint leaf extract.

Elevation, latitude and weather all affect the timing and intensity of fall colors. Higher elevations and northern latitudes produce earlier autumn colors in trees. In general, autumn weather with lots of sunny days, dry weather, and cold, frostless nights will produce the most vibrant palette of fall colors. Some trees that can produce vivid colors include maples, gingkos, aspen, birches, Japanese maples, liquidamber, cherry, redbud, Chinese pistache, and dogwood. 

In the Central Valley we usually don't get the glorious colors like the Sierra Mountains or the east coast, but we do get some color which usually starts in early November. So, enjoy the autumn jewels since it occurs only for a brief period each fall!

Denise Godbout-Avant has been a UCCE Stanislaus County Master Gardener since July 2020.

If you have an ash, Chinese pistache, crape myrtle, flowering pear, ginkgo, liquidambar or any other tree that is showing early fall color, pay attention. Early fall color may indicate that the tree is in trouble.

Trees normally begin to show fall colors in late October, especially after a couple of cold nights. If you are seeing orange, yellow, red, burgundy, and purple leaves on deciduous trees this time of year, it's a symptom of stress. You might not be able to do anything to correct the problem now, but much can be done to prevent a repeat next fall.

First, determine the source of the stress and correct it. Look closely at the tree. Check for wounds on the trunk from mechanical injury or sunburn. If early fall color is the result of wounds, take steps to prevent further wounding. The trunks of young trees can be protected from string weeder damage with plastic sleeves. Better yet, place chip mulch on the soil around the tree to remove the temptation to mow or weed right up to the trunk. 

Determine if the tree is growing in a site where the roots may be restricted by pavement or buildings. Is it possible the roots were recently cut? Root disease, recent disruption to roots from construction or grade changes, surface soil compaction from vehicles or foot traffic and girdling roots can also cause trees to develop early fall color. If surface compaction is a problem, loosen the soil by cultivating to a depth of 4 to 6 inches. This should improve moisture and oxygen penetration. Follow up by watering the tree deeply. 

In some cases early fall color is caused by problems that are not easy to correct. For example, trees with poorly developed root systems - as sometimes occurs when root bound trees are planted  - are usually permanently stunted. Such trees often show fall color 2 to 3 weeks earlier than healthy trees of the same species. 

The best way to prevent stress and early fall color is to make sure the tree receives sufficient deep water during the summer.  If you haven't already, deep water your tree. Sprinkler water does not provide adequate water for trees, so supplement with a hose, focusing the water underneath the tree canopy. For mature trees, water needs to penetrate to a depth of 12-18" to provide enough water.

For questions about your trees, contact the Master Gardeners at (209) 525-6862 or fill out this form http://ucanr.edu/ask/ucmgstanislaus  

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. 

Did you know that plants can suffer sunburn injury just like people? Sunburning of plants is actually a common and serious problem in the San Joaquin Valley, especially after a few days with temperatures over 100° F.

Sunburn is damage to leaves and other plant parts caused by a combination of too much light and heat and insufficient moisture. The first symptom of this problem may be leaves that appear dull or wilted. A yellow or brown “burned” area develops on the leaves, which then dies beginning in areas between the veins. 

The best way to avoid sunburn is to choose plants that are adapted to the planting site. Trying to grow shade-loving plants in full sun is asking for sunburn problems. But even sun-loving plants will suffer sunburning of leaves if the plants are growing in dry soil. You need to provide your plants adequate irrigation water to prevent most sunburning problems.  If you notice the symptoms early enough, you may be able to restore the color to sunburned leaves before they killed.

Sunscald, also sometimes called sunburn, is damage to tree or shrub bark caused by hot sunshine. Sunscalded bark becomes cracked and sunken, and is susceptible to attack by wood-boring insects and wood-rotting fungi. In fact, I almost always find evidence of flatheaded borer injury in trees that have sunscalded bark. Sunscalded trunks and limbs can develop cankers, become girdled, and die.

Sunscald often occurs on young woody plants. Their bark is thin and may not tolerate exposure to direct sun because they were grown in nurseries where their trunks were shaded. Older trees can be damaged if you expose branches to the hot sun by pruning heavily, especially during the summer months. Removing taller trees that provided shade, or adding pavement or buildings that reflect light onto plants can also lead to sunscald. Even in well-watered soil, sunscald may injure bark if plant roots are unable to absorb enough moisture when it's hot.   

You can prevent sunscald through proper planting and pruning. Prune newly planted landscape trees very little or not at all. Leaves not only shade the bark, but manufacture foods necessary for root growth. If there is no foliage growing along the trunk of a newly planted tree, paint the trunk with white interior latex paint, diluted 50 percent with water. Old bark that has been recently exposed to the sun by pruning or limb breakage can also be painted white.  Wood chips and other organic mulches can reduce reflected heat and light, thereby reducing the danger of sunscald.

Each tree and shrub that you plant is adapted to certain amounts of light, depending on species and previous growing conditions. Plant growth can be retarded by too much or too little light. Too little light causes pale foliage and elongated, spindly shoots. Too much light can cause leaves to discolor.  For example, the leaves of camellia plants, which are adapted to partial shade, take on a yellowish tinge when exposed to too much light. The typical leaf color returns when plants receive normal light, but a long period of the wrong light intensity will cause plants to become susceptible to other problems and possibly die. 

As always, it's important to plant species that are well adapted to the amount of light available in your garden. Also, avoid changing the environment in any way that significantly changes the amount of light your established plants are receiving.

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.

Rho Yare is a first year Master Gardener in Stanislaus County.

The other day I was thinking that with so many people unable to work because of businesses forced to close, children with no school or day care, and those “self-quarantining” for health reason maybe this would be a good time for you to try gardening.

In most cases plants are forgiving, will not lecture you, give away any of your secrets, request money nor the car keys. Those plants in your yard, patio or on the balcony might just need a little love and right now you have the time.

If you are fortunate to have some land around your home perhaps this would not only give you other options of things to do while at home but make your world more attractive and interesting. Wander round your space and reacquaint yourself to what is planted there. This might be a good time to weed, trim, or remove shrubs or plants that are no longer looking their best. Perhaps checking the irrigation system or planning some changes that you might like to make to your outside environment.

At this point all the health experts are telling us that spending time outside is good for us if you are healthy and if we do not congregate with those not in our immediate living situation. Including young people in the exploration of your garden/yard is a wonderful way to talk to them in a relaxed setting and listen to their fears, interests, and frustrations. If there are no young people in your home, then this might be a perfect time for a solo garden experience.

You could review those things you wished you had said or practice what you will say to friends, co-workers, or someone who you find interesting. I find that I can solve all the problems of the world, of my family, and make lots of plans while pulling weeds. Most of the time my heated solo discussions make my garden cleaning speed along.

You could invite that person who shares your home to join you outside in your gardening area to keep you company while you work. A change in routine and space can sometimes produce surprising results. Sharing this time might make communication easier and perhaps alleviate some fears and anxieties about COVID-19 and the future.

Getting away from all those screens and looking at something besides the inside of your home could be beneficial to your mental wellbeing. If you have a patio or balcony you can still garden and have the benefits of exercise, stress reduction, beautification, education, and possibly a food source.

Children are especially excited when the seeds they plant in containers begin to sprout little green leaves. You might already have some containers that can be used for your small space garden.

Or consider the next time you make that trip to purchase home supplies at a grocery or variety store you add a container, some soil, and a package or two of seeds. It is amazing how your gardening experiment will be interesting, challenging, and have the bonus of the “I did this” factor for adults as well as for young people.

Although some resources have been curtailed the Internet has many sites that can give you gardening advice. Another source is the UCCE Master Gardeners of Stanislaus County. Master Gardeners are volunteers who have completed a rigorous course of classes and would welcome your questions, offer free advice, and encouragement. Leave a message for us by phone (209) 525-6802 or email ucmgstanislaus@ucanr.edu 

Adding gardening and outside time to your schedule might help with some of the long and possibly boring days ahead. None of us want to be “stuck” in our homes but expanding our horizons to a little beyond the four walls just might make this time more interesting for you and give you some new skills and interests.