Welcome to our new tree column, "Ask your local arborist." Each month, arborists from the Davey Tree Expert Company in Menlo Park will discuss a tree-related topic from general care to planting tips and tricks to how trees can impact your property and community, as well as answer your questions. If you have a tree-related question or an idea for a topic to discuss, email them here. Arborists may make house calls, when needed, to assess tree questions on your property.
As summer nears and people head outdoors – and often under the cool shade of a tree – it's not unusual to get inquiries from local residents wondering how to keep their trees healthy during the area's hot and dry months. Common questions include: Why are my tree's leaves turning yellow and falling? How much water do trees need each week during summer's dry spell? Is it OK to prune my tree during the summer? How do I know if my shrubs have bugs?
These are all good questions. As the higher temperatures and brighter sun make their way in, it becomes crucial to prioritize the preparation of your trees and learn how to properly care for them throughout the season. Our trees work hard to keep us cool, but they need protection from the hot sun, too.
When caring for your trees during the hotter months, there are lists chock-full of things that you can be doing, but here are three non-negotiables for summer tree care:
Make sure your trees stay hydrated
Proper watering can make or break the health and longevity of a tree’s life. Too much water can rot the root system, while not enough water can cause the tree to become dehydrated (just like we do).
If you see sections of yellow leaves, you want to make sure to check your soil moisture. Your tree could be suffering from heat stress. Summer leaf yellowing is a sign that your tree is trying to conserve water. But just as your tree could be telling you it is underwatered, it also could be telling you that it is overwatered.
To determine whether your tree needs water, poke a long screwdriver into the dirt beneath the tree. If the soil is saturated with water, you might be irrigating the tree too frequently.
If the screwdriver is hard to push in, water your tree. The best times to water are in the morning before it gets too hot or in the evening, once the sun goes down. A typical rule of thumb is to water 5 gallons for every inch of trunk diameter each week during the dry summer months.
Using a good fertilizer can help keep the root systems cool and lock in moisture during hotter months. Most trees prefer a slow-release fertilizer, however, you should consult your local tree expert to see which fertilizer is best for your property
Keep your trees tidy
Monitoring your property means the difference between a cared-for healthy tree and a struggling landscape. Getting to know your trees and shrubs can be vital to their health. Check frequently for pests and diseases that could be affecting your trees and property. Even just a simple walk-through while you enjoy your morning coffee can make a difference. Take note of how the trees look, see if anything catches your eye and might need some immediate attention. Look for discoloration, bugs, leaves that don’t look right or bark that is falling off branches.
Keep your trees and shrubs tidy. If you see dead branches, prune what you can and leave the rest to the pros. A good rule of thumb is that if you find yourself on a ladder to reach dead branches or if your tools go above your head at any point, call an expert to do the job. If you are a composter, any tree debris (dry leaves, twigs, wood chips from larger branches) can be added to your pile.
Manage pests and diseases
Pests and diseases are bound to show up in your landscape, but there are things that you can do to manage and protect your property.
Signs that a tree is being affected by pests or disease are loose bark, yellowing or wilting of leaves, leaves falling out of season, and thinning of the canopy.
Specific pests and diseases to be on the lookout for include:
• White flies on citrus trees, mainly Meyer lemon trees. Horticultural oil can manage them.
• Thrips on photinia and rhododendron. These are tiny black bugs on the back of the leaves that "ghost out" or turn the leaf a silver color. An arborist can treat the plant with a systemic soil injection, a method that places the pesticide below the mulch or turf and directly into the root zone of the tree and kills bugs as they feed.
• Fireblight on flowering pear trees and Catalina cherry trees. These pests will make leaf ends look like they are burned.
• Anthracnose leaf disease on sycamores and ash trees. This can cause premature leaf drop.
Jeff Newborn is a local arborist at The Davey Tree Expert Company in Menlo Park, which serves communities on the Peninsula, including Menlo Park, Atherton, Palo Alto and Redwood City. Newborn can be reached at 866-923-5658.