It's hot summertime and your trees have brown foliage on them. Is it time to panic, fertilize, spray for bugs, or water for three days straight?
In some cases brown foliage is normal in the summer, but in other cases it is a sign of serious problems. The descriptions below should help you evaluate your particular situation. Take a good look at where and how much brown there is in your tree. Then get professional help if needed.
This type of brown foliage is normal on Coast Redwoods in the summer.
Redwoods are evergreen and have green foliage year round. But in the late summer, some of the older growth farther from the branch tip dies and falls off. This is completely normal and not a problem.
The tree on the right is in trouble. Most of its foliage is brown and the top of the tree has no foliage at all. This is not normal and is a cause for urgent action.
We often see this in Redwoods that are getting too little water. Since Coast Redwoods are native to California, people often think they can go without summer irrigation. They are indeed natives, but to the cooler coastal ranges of Northern California where fog frequently cools the hot temperatures.
In our hot-summer Sacramento Valley, Redwoods must be irrigated so that the trees can survive. To keep them thriving, they need a moderate to high level of irrigation. This being a drought year, people are reducing how much they water. But that can put enough stress on Redwood trees that they are severely damaged or die.
What should you do if your tree looks like these?
This situation calls for expert advice. This is a job for an experienced arborist who will come and inspect your tree and discuss with you what needs to be done. If you don't have a regular arborist, here is a listing for Certified Arborists in your area.
In the meantime, dig a small hole 12"-18" deep at the edge of the canopy and see if the soil is dry, wet, or moist. Your tree needs moist soil, it should stick together but not be muddy.
If you cannot dig, use a moisture meter (not as accurate in sandy or rocky soil, but better than nothing).
If the soil is dry, apply water slowly so it soaks in and doesn't run off. You want to wet the entire area under the canopy and plus about 10' beyond. You can use a sprinkler or soaker hose. It may take several hours to get water deep enough to reach the majority of roots. Try not to let sprinklers or spray hit the trunk or foliage directly. This water should sustain the tree for days until you can get expert advice on what to do.
What not to do for your ailing Redwood -- don't fertilize and don't spray for "bugs". Fertilizer is not a cure-all for trees. Most fertilizers are salts and adding them to soil that is too dry can cause even more damage. Spraying or treating plants with insecticides only works if you know what the attacking insect is and how to treat it. University of California Integrated Pest Management has information on pests and pest management. You can look up what type of plant you have and learn about possible pests and diseases and what to do about them.
What else could be causing brown foliage on Coast Redwood Trees?
Redwood trees with adequate water are usually pretty resistant to pests and diseases. Some pests and diseases can cause twigs or branches to die like the tree in the photo, but these are usually not serious.
Redwood trees in areas where they do not receive enough summer irrigation or are irrigated with recycled water are more prone to problems. Recycled water has higher levels of salt, which redwoods cannot tolerate.
Too much water can also be a problem if the soil is constantly saturated.
Root damage from trenching or construction, or fill soil in the root zone can also cause brown foliage. Consult your arborist if you have concerns on how to preserve the health of your tree.