- Author: Ed Perry
Trees normally begin to show fall colors in late October, especially after a several 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, and improve the health of your tree before spring.
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.
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.
- Author: Ed Perry
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.
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.