A walk in your garden is good for you and for the garden. This is a chance to admire your gardening efforts and calm your mind. The garden benefits from your walk because you can spot problems before they cause major damage. It’s important to keep an eye on established trees and shrubs because replacing them will not only involve expense and effort, but the loss of any one of these garden features can alter other aspects of your overall landscaping.
In the midst of the summer heat, it is not entirely unexpected to have fallen leaves on an established shrub or tree in the garden. Of concern are entire sections of the plant showing withered or browned leaves that may or may not drop. Especially when it happens quite suddenly, like over a few weeks, it warrants investigation.
Plants transpire water vapor through their leaves.
Leaves have stomata or openings in the outer layer of leaf cells for the exchange of oxygen, carbon dioxide, and water evaporation. The evaporation of water cools the plant in hot weather. When less water is available, the stomata close to reduce water loss during the release of oxygen and the absorption of carbon dioxide. A significant reduction in water available to the roots will be demonstrated in changes in leaf color and texture. In the case of a large shrub or tree, on a hot, dry day, water loss due to transpiration can reach hundreds of gallons.
Early detection of signs of stress due to reduced water availability can maintain plant beauty and can save lives.
Irrigation System Concerns
If the shrub is on an irrigation system, this is the first place to check. Is the sprinkler timer malfunctioning? Even minor power outages can alter the irrigation schedule. The valve wiring may have been damaged or come loose. Does the irrigation timer setting need to be adjusted to match the season? If the irrigation system waters during cold, rainy days, the soil will become waterlogged and the roots may become unable to absorb oxygen and die. Tree trimming or lawn equipment may have damaged a transmitter. The drippers have a small opening to deliver the slow flow of water just to the root zone. These small openings are very prone to clogging from well water salts. If the irrigation system contains impact sprayers, there may be an obstruction blocking the spray stream. This prevents it from covering the full range of the spray arc. The plant itself may be clogged with new growth or the sprayer mechanism may need cleaning or oiling. If the water now sprays on the crown or leaves of the plant, it can cause fungal diseases. This can be observed as dark spots on the leaves, fungal growth or dead branches in the plant.
Chewing rodents vs irrigation systems
Especially under a tall shrub, rodents looking for water will gnaw through the drip lines, causing excess water in one area and virtually no flow further down the line. Unfortunately, a large shrub can provide shelter for a rodent restaurant for mice, voles, gophers, squirrels and rats. This problem can be detected by manually turning on the irrigation system and listening for areas of abnormally high flow. One solution is to replace the drip emitter system with a thick plastic in-line drip pipe. The tube is less vulnerable to small chewing rodents and can also be flushed to remove mineral deposits.
Have there been any landscaping changes?
Changes in other areas of the garden can cause the plant to receive significantly more sun or shade in certain areas of the plant. It could be from the pruning you did last fall, or maybe a neighbor built a structure that now shades the plant. An increase or decrease in the sunlight the plant receives affects the amount of water it needs for optimal growth. Or perhaps the removal of an area of grass may have reduced the water supply the plant expected. Tree roots extend beyond the tree canopy and seek additional water, especially on hot summer days.
A walk in the garden benefits the gardener and the garden
There are also specific plant problems that can cause leaf changes. There will be another walk around garden article to cover more topics. The Master Gardener website has a wealth of information on all aspects of plant care and UC Integrated Pest Management. As part of pest control, there are specific solutions to rodent invasion. Enjoy your walk in the garden and your plants will benefit from early observation of problems while they are being corrected.