- Author: Judy Quan
Editor's Note: This blog post originally appeared on the Master Gardener Program of Alameda County website.
Thinking of planting a street tree?
Do you have space for a tree in the parking strip, that no man's land between the sidewalk and the street? If you do, there are many advantages to having trees grow in that space.
Why plant a tree?
- Trees are beautiful and welcoming. Trees have a calming and healing effect on people and community. They add value to the neighborhood.
- Trees help us to live with warming temperatures. Street trees, part of the landscape, help to reduce the effect of urban heat islands by providing cooling shade to sidewalks, buildings and other structures that capture heat.
- Trees fight climate change. Trees absorb and store carbon dioxide, also reducing greenhouse gas emissions to the atmosphere.
- Trees add to the natural habitat. They can provide habitat for birds, pollinators and other wildlife.
- Trees improve the local environment. They provide windbreaks, capture storm water runoff and muffle urban noise, among many other things.
“Unfortunately, their [street trees'] average lifespan in our cities is less than 1/4 of their potential due to poor selection and care.“ Janet Hartin, Environmental Horticulturist, UC Cooperative Extension, Trees for Tomorrow Start Today
Tips on Street Tree Selection
Gather information about the site (your parking strip)
- Check with the city. Find out whether the homeowner is allowed to plant a tree. In some cities, only the city can plant in the parking strips.
- Power lines? You need to determine whether the power lines are on your side of the street or not. If they are, then you are limited to small trees that are "ok" to plant under the high voltage lines.
- Width of parking strip? Then you will need to measure the width in inches of the parking strip where you are planning to plant your tree. Then you can compare your dimensions to those of the suitable tree basin width.
- Other considerations? Think about the type of soil you have, the availability of water, shade, proximity to buildings, and wind conditions.
Look around in your neighborhood to see what you like and don't like in street trees.
- Seeing a mature, full-grown specimen of a particular species of tree in your neighborhood is very different from seeing a photo of the tree on the internet. Often the in-person view will give you a really good feel for a tree's true appearance and it may also show you other aspects such as the amount of litter from flowers, seeds and leaves.
- Talk to your neighbors about the trees in your neighborhood.
- As you drive or walk around the city, look around at the street trees and take note of the ones that you like and where they are located.
- If your city has a public works department, parks department or an urban forester, you may be able to get help with the identification of the trees and may also get recommendations.
What trees are approved for street trees in your area?
- Many cities, but not all, have an approved list of street trees. These are the trees that are officially approved for planting in the parking strip. The list often has additional information as to how to select trees for a particular site.
- Many cities have an urban forester who manages the selection and care of tree populations in the urban setting. Often the forester may be part of public works or parks division of city programs. Sometimes there are programs that promote tree planting and financial incentives might be available.
- Local tree lists and planting information for some of the cities of Alameda County. Please contact your city hall or public works for information in your city.
Unincorporated communities of Ashland, Castro Valley, Cherryland, Fairview, San Lorenzo, and Sunol
What are the characteristics of the trees on your list?
- Research both the common name and the botanical name, so you will get more information on the tree including information on litter issues, root damage potential and mature size.
- Trees are either deciduous (lose their leaves in the fall) or evergreen (keep leaves/fronds/needles year-round). Just because a tree is evergreen, does not mean that you don't have leaf litter. Evergreen trees may drop some leaves more-or-less year around instead of the once-a-year leaf drop in the fall.
- Once you have narrowed your list down to a few trees, you might give the city a call and find out if there is information on where you can see that type of tree locally.
- Minimize potential damage to the sidewalk. To avoid or minimize sidewalk/curb damage/lifting, choose a smaller tree that fits your parking strip and be sure to water the tree appropriately.
Care of trees … things I wish I had known
Unfortunately street trees are sometimes not planted with the ideal tree selection/planting guidelines. Fortunately, many of these problems can be corrected if noticed early on, soon after the tree has been planted.
Here are some practical tree care tips from Janet Hartin, a UCCE horticulturalist.
Trees for Tomorrow Start Today
How to Avoid Common Ailments of Landscape Plants
You may find that you will use this information on care of trees directly if you end up planting your own tree, or you might find that you will use the information to make sure your tree is planted correctly by the city/contractor hired by the city.
4 Tips on Planting trees
- Plant the tree in native soil, with NO amendments or compost.
- The hole for the tree should be the same depth as its container and at least 2-1/2 times wider. Make sure that the flare of the crown is above ground. Remove the soil, gently place tree in hole, fill with original soil around the plant.
- Prevent circling and kinked tree roots. Straighten or cut off circling or kinked roots. Roots circle or become kinked when there is no space for roots to grow out, such as in containers or small plant holes or organic-filled plant holes. When holes are filled with organic material, roots may never grow beyond the boundaries of the original hole because the roots prefer the richer organic material.
- Check/remove the tree ties or stakes. Remove any tree ties that are too tight and cut into the tree trunk or branches. Tree ties should be loose enough so that your tree can sway with the wind. This movement allows the trunk of the tree to develop more strength and flexibility over time. The ties and stakes may be removed as the lower trunk becomes stronger and self-supporting. Find more detailed information about when to remove ties and stakes here:
- Apply mulch 2-4 inches deep around your tree. Keep all plants and mulch several inches away from tree trunks.
8 Tips on Watering Trees
- Keep tree trunks dry. They should not come into contact with water from sprinklers or hoses.
- Apply the right amount of water at the right time.
- Water newly planted trees regularly for a full season Many newly transplanted landscape trees die from the soil drying out too much between waterings. Regularly water newly planted trees. The tree root systems are small and need to be kept moist for a full growing season.
- Water the newly planted, drought-tolerant species too. This schedule of regularly watering newly planted trees holds true for drought-tolerant species as well as those that require more water. Once plants become well-rooted they should be watered less often but for longer periods of time.
- Water halfway to dripline and beyond. Since tree roots spread outward as well as downward, water should be applied beyond the dripline of the tree, if possible.
- Most established trees need water too. Most trees in California need supplemental irrigation above and beyond the naturally-occuring rains, especially in times of drought. Water established trees less often but more deeply to encourage deep rooting and structural balance above and below ground.
- Trees need to be watered slowly and deeply. If you use a garden hose, apply the smallest trickle of the water slowly, moving the hose every few hours to water the entire area around the tree. The deep watering encourages roots to grow downward and help prevent sidewalk damage.
- Do NOT water trees on the same irrigation/drip system as the one used for lawns and groundcovers. The light, frequent watering every few days that is appropriate for lawns/groundcovers discourages the deep growth of tree roots.
Tip on Pruning Trees
Prune trees only as needed and avoid topping them. Hire a credentialed and knowledgeable arborist to correctly care for your trees. Find a list of International Society of Arboriculture Certified Arborists in your area here.
Thinking about tree selection and predicted future climate change
You might select trees that are more suited for the future warming trends. Here is a very interesting article from the UCANR Green Blog on using location for time. For instance, in 2099 the climate in Berkeley may be more like that of Santa Ana.
“Urban foresters in inland cities of California should begin reconsidering their palettes of common street trees to prepare for warmer conditions expected in 2099 due to climate change,” said the study's co-author, Igor Lacan, UC Cooperative Extension environmental horticulture advisor in the Bay Area.
Street trees are important in so many ways:
Trees provide beauty and calm, help us to live with warmer temperatures, fight climate change, provide a natural habitat for wildlife including birds and pollinators. It is important to properly select, plant and care for street trees, so that the benefits of each street tree can be realized to its full potential.
Still need help?
Confused or need more information? Email us at acmg@ucanr.edu. Or contact us through our website.
More resources on the importance of trees, tree selection, tree care:
Four articles with more details on tree selection and tree care from Janet Hartin, UCCE horticulturalist:
- Trees for Tomorrow Start Today
- How to Avoid Common Ailments of Landscape Plants
- Landscape Tree Irrigation 101
- Plant a Tree. Leave a Legacy!
If you want more details of how to plant a tree with photos, here is a good source: “Save the Planet, (Learn How to) Plant a Tree” by Dr. Linda Chalker-Scott who is an ISA certified arborist and an ASCA consulting arborist. She is also WSU's Extension Urban Horticulturist and a Professor in the Department of Horticulture.
The importance of trees to cool urban heat islands
Lush urban forests can help communities face climate change
Trees also can have calming and healing effect on people and community
Cities in California inland areas must make street tree changes to adapt to future climate
Cooperative Extension San Joaquin County
Really good source of information on arboriculture and getting the most benefit from trees through good management.
UC study seeks street trees that can cope with climate change
- Author: Janet Hartin
Do you have Spring Fever? If you have adequate space, why not leave a legacy to your children's children by planting a tree? When the right species is planted in the right location and receives the right care, landscape trees can be enjoyed for 100 years or more.
Urban trees cool and shade urban heat islands, absorb and store carbon, produce oxygen, filter pollutants from air and water, reduce soil and water erosion, reduce internal energy needs and related costs, provide habitat, and beautify neighborhoods. Sadly, the average lifespan of our landscape trees is less than 20-25% of their potential due to poor selection and care.
Selection and Care Tips:
Plant in Spring or Fall. Avoid planting landscape trees during the heat of the summer. (Deciduous bare-root fruit trees, on the other hand, should be planted during the winter when they are dormant.)
Choose recommended species for your climate zone. Select trees based on your Sunset climate zone (zone 13 for Coachella Valley) because they are more precise than USDA zones and include information related to high temperature adaptation s as well as low temperatures which is the basis of the USDA zones).
Choose recommended species for your microclimate (shade/sun, soil conditions,water requirement, available space, etc.).Two reliable search engines that allow users to search by multiple criteria (size, water needs, flower color, ecosystem functions, pest susceptibility, etc.) are: Urban Forest Ecosystem Institute : https://selectree.calpoly.edu; California Native Plant Society: https://calscape.org/search.php. 'Lush and Efficient' is also a very useful publication produced by the Coachella Valley Desert Water Agency. Download it here: http://www.cvwd.org/DocumentCenter/View/813/2006-Lush--Efficient-Revised-Edition-PDF?bidId=as is Water Use Classification of Landscape Species IV: http://ucanr.edu/sites/WUCOLS
Four species that we have recently identified in our research on heat and drought resistant trees that are highly recommended for the Coachella Valley are:Netleaf Hackberry (Celtis reticulata), ‘Maverick' Mesquite (Prosopis glandulosa), Pistacia ‘Red Push' (a hybrid between P. atlántica × P. integerrima) and Desert Willow ‘Bubba' (Chilopsis linearis)
Avoid circled, girdled roots. Remember to inspect the root system of container trees. Avoid specimens with severely circled and girdled roots. Root pruning will not solve the problem and the resulting tree is much more prone to failure later. This occurs because the upper portion of the tree continues to grow and expand while the root system lacks the breadth and architectural strength to support the tree. Many times a tree will look fine for several years and - seemingly - very suddenly, topple in winds that otherwise it could sustain with a more adequate root system. Only when the tree falls does the owner actually notice firsthand that the root system is the same size it was when the tree was planted years before!
Check drainage before you plant. Dig a hole where you are planning on planting the tree, fill it with water, and make sure it completely drains within 24-hours. If it doesn't drain, don't plant a tree there. In some cases, trees are carefully selected based on species and location only to perish ten or more years later due to poor drainage and water-logged soil. Trees often die in these situations due to a lack of aeration setting them up for disease-causing fungal pathogens. tree planting hole drainage test tree planting hole drainage test Planting the tree.
Dig a planting hole at least 2-1/2 times the width of the container (in clay or compacted soils make the hole at least 4-5 times wider) up to two inches shallower than the depth of the tree in the container to compensate for settling. Use a shovel or trowel to roughen the soil on the sides of the hole to encourage root growth into the native soil. Remove the tree from the container along with any loose soil that covers the lower part of the trunk. Carefully place the tree in the planting hole, keeping the trunk flare (the area where the trunk widens and connects with the roots) 1-2 inches above the existing grade. Gently fill the hole with the same soil that was removed. Do not add soil amendments or compost, another common cause of circled and kinked roots. Water the tree regularly until established (one or more seasons).
Water immediately after planting making sure to moisten the entire root system and a few inches below it. Many recently planted trees die due to the common misconception that they require little or no water if they are native or low water using species! Recently transplanted trees have a small volume of roots that dry out very quickly. Water trees separately from turf and surrounding higher-water using plants.
Water newly planted trees regularly through the first season. Trees in sandy soils require more frequent watering than do trees in heavier soils with appreciable clay content. Heavier soils absorb water slower but retain it longer and should be watered longer but less often. (After trees are fully established, irrigation frequency should be reduced but more water should be added during each irrigation.) Avoid staking trees unless necessary.
Stake trees only if they were staked at the nursery and/or if they are planted in a wind-prone area. Remember to loosen ties on nursery stock before they girdle the trunk. Gently secure any tree requiring staking with two opposing flexible ties on the lower half of the tree, allowing the tree to gently blow in the wind to encourage lower trunk strength. Avoids staking trees tightly, restricting flex. As the tree matures, remember to loosen ties with the goal of removing stakes entirely if the tree becomes self-supporting.
Pruning. Avoid heavy pruning at the time of planting. Remove only broken branches, crossed branches and suckers at the base of the tree. Don't top your trees! (More on this next month.)
Fertilizing. Most trees have received adequate nutrition in the nursery and do not need fertilizer at the time of planting.
Mulching. Apply a 2-4 inch layer of mulch three or more inches away from the tree trunk. Organic mulches such as woodchips and compost should be applied and maintained at a depth of 3-4 inches to prevent weed seeds from sprouting. Inorganic mulches (gravel, pebbles, etc.) should be maintained at 2-3 inches. In fire-prone areas, organic mulches near the urban/forest interface should be avoided. Remember to irrigate below the mulch.
For more information on tree planting and care and all other home gardening and landscape topics, contact the UCCE Riverside County Master Gardener helpline here in the Coachella Valley: anrmgindio@ucanr.edu
- Author: Elaine Lander
With the recent time change along with a change in temperatures, landscaping practices for pests need some adjusting too. We're sharing a few recommended tasks to help prevent insect pests, diseases, and environmental disorders in landscapes. Looking for additional tips? You can subscribe to our Seasonal Landscape IPM Checklist for monthly landscaping reminders delivered straight to your email inbox.
Frost Protection
Irrigation
Adjusting water schedules is an important part of integrated pest management. Different plants have different watering needs and too much or too little water can damage or kill plants. Reduce irrigation frequency or turn off automated systems if rainfall is adequate or irrigate deeply if the weather is dry. Learn more about irrigating fruit and shade trees and shrubs on our website.
Prune
Deciduous trees and shrubs such as apple, crape myrtle, pear, and peach need to be pruned to maintain their structure and health. Proper pruning can also help manage and prevent certain pests. Our website has plant-specific pruning information for a number of fruit, nut, and landscape trees. Be sure to remove dead, diseased, and borer-infested wood.
Sanitation
Now is the time to clean up old fruit and nuts under trees to avoid harboring pests. Removing fallen leaves from beneath fruit trees and roses will also help reduce insect and disease problems. This practice of sanitation is a key component of integrated pest management to prevent and reduce pests. See our website for additional sanitation tips in your landscapes and gardens.
We're looking for your feedback! Please consider taking a quick, anonymous survey to help us serve you better: https://bit.ly/2ZJJVEI
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What is Armillaria Root Rot?
Armillaria root rot is a severe fungal disease that affects trees, woody plants, and some herbaceous plants including palms and succulents.
Also known as oak root fungus, Armillaria root rot can rapidly kill trees and presents a challenge to management since infected woody roots can persist for years underground. No plants are completely immune to Armillaria root rot, so prevention is key. Deeply planted trees are often more susceptible to this disease.
The distinctive “honey mushrooms” growing from the base of a tree signals an infection, but they may not always be present. Other visible symptoms include flat cankers on the trunk, wilting, and canopy thinning.
In UC IPM's new publication Pest Notes: Armillaria Root Rot, UCCE Advisors Jim Downer and Igor Lacan provide research-based techniques for prevention and management of this common disease of landscape trees and plants, discuss the life cycle of the fungus and damage to the host plants, and include color photographs to aid in identification.
You can browse the full list of resources on invertebrate pests, diseases, weeds, vertebrate pests, and management methods on the UC IPM website.
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- Author: Janet Hartin
Did you know that many landscape problems are not caused by either diseases or insects? In the majority of cases the culprits are poorly drained soils, irrigation issues, trees in too tight of quarters or improperly pruned, and other non-living (abiotic) maladies. The good news is that most of these issues can be prevented. Follow these suggestions to steer clear of common abiotic problems in your landscape. Following these suggestions will also help your plants stay healthy and better able to fend off insects and diseases they would otherwise be vulnerable to.
Select plants that grow well in your climate zone. Choosing the right plant for the right place is a sure way to green up your thumb and keep your plants healthy and attractive. The Sunset climate zone map is a great resource for finding out what climate zone you are in. These zones are more accurate for most areas of California than USDA plant hardiness zones since they are smaller and take into account more relevant factors than do the USDA hardiness zones. An exception are mountain communities in which case either resource works equally well. Click here to find your Sunset climate zone https://www.sunsetwesterngardencollection.com/climate-zones and here to locate your USDA plant hardiness zone: https://planthardiness.ars.usda.gov/PHZMWeb/.
Select plants that will grow well under various ‘microclimates' around your home. Microclimates are smaller areas within your larger climate zone that further determine the suitability of a plant for a specific spot. Typical microclimates are sunny or shady areas, sections of your yard that get splashed by chlorinated water from a pool or spa, narrow strips in side yards that are too small for a large-growing tree, and poorly drained soil with not enough air to support plant growth. While all plants need adequate space, trees need the most. While a beautiful shade tree like a ornamental fig, magnolia, or rosewood might be tempting, they all need about 3,000 cubic feet of space underground and 50 feet or more above ground clearance at maturity. Otherwise roots can buckle sidewalks and driveways and branches can interfere with utility lines. There are many smaller-maturing trees such as acacia, mesquite, crape myrtle, and dozens of other species that won't cause these problems and are good choices for smaller areas.
Be sure to do adequate research on the expected size of a tree you're interested in before making a purchase. Care tags, UC Cooperative Extension Master Gardeners, and nursery and garden center personnel are all good sources of help to match a plant's requirements regarding space, sun, and shade and their tolerance to salt spray, problem soils and other restrictions with conditions in your own yard. Three excellent searchable plant databases for finding suitable plants for your climate zone and microclimate conditions are: Urban Forest Ecosystems Institutes (https://selectree.calpoly.edu/); California Native Plant Society (https://calflora.org/); and UC's California Center for Urban Horticulture Water Use Classification of Landscape Species (WUCOLS) (https://ccuh.ucdavis.edu/wucols-iv).
Apply the right amount of water at the right time. Many newly transplanted landscape trees, shrubs, and flowers die from the soil drying out too much between waterings. Their root systems are small and need to be kept moist for the first few weeks in their new home (or a full season for a tree). This holds true for drought-tolerant species as well as those that require more water. Once plants become well-rooted they should be watered less often but for longer periods of time. Water slightly below their current root system to encourage downward growth. This practice is especially important for trees since it promotes deeper roots better able to support and stabilize above-ground growth.
Since tree roots spread outward as well as downward, water should be applied beyond the dripline of the tree as well. Some soils never fully drain leading to low oxygen levels than hamper tree growth and can eventually kill the plant. To test for adequate drainage before planting a tree, dig a hole at least one foot deep and one foot wide and fill it with water. If it doesn't drain in one day or less a tree should not be planted at that site.
Hydrozone (place plants with similar water needs together). If your landscape is irrigated on an automated system, you can save water and reduce your water bill by grouping plants according to their water need. Divide your landscape into very low, low and medium water use hydrozones at the design stage and remember to replace any dead plants with new ones requiring a similar amount of water. This allows you to fine tune how often and how long to water each zone. Hydrozoning also helps you stay within a medium or even low water tier even if you have designated high water use areas for vegetables and fruits that generally require higher amounts of water than most landscape plants.
Prevent soil compaction and poor drainage. Avoid adding soil amendments to tree planting holes. Trees need adequate underground support as they grow upward and become heavier. Trees in either too small of planting hole or in holes where compost or other organic soil amendments have been added may grow in circles around the hole, never venturing outward beyond the constraints of the hole. Trees may eventually topple, causing injury to people and nearby structures. Instead, dig a hole at least twice the width of the container and at the same depth the tree you will be transplanting came in, remove the soil, gently plant the tree, tamping the original soil around the plant. Remember to water the newly planted tree in well and keep the rootzone moist the first season as discussed above.
Add soil amendments (including compost) to soil before planting small ornamental plants and edibles. They add valuable organic matter to the soil, improving aeration and drainage in heavy clay soils and water-holding capacity in sandier soils. Compost also adds valuable microbes that break down the organic matter improving overall soil health. Mix enough soil amendments into the soil so that the final volume contains about 40% soil amendments and 60% original soil. Make sure that the soil amendment is mixed into the soil evenly and completely. Do not add soil amendments to tree-planting holes to avoid circling roots.
Correct high pH (alkaline) soils. Southern California soils tend to be alkaline, with average pH ranges from 7.1 – 7.6. (Most plants prefer a neutral pH of 7.) Highly alkaline soils often tie up nutrients necessary for plant growth - such as iron, zinc, and manganese – making them unavailable to the plant. Once the pH is reduced, the problem is often resolved.
Avoid salt damage. Damage due to too much fertilizer or water high in certain salts (such as chlorinated swimming pool water) can cause brown leaf margins and leaves that look scorched. Over time, the damage gets worse and sensitive plants may die. One way to reduce the chance of too many salts building up in your soil is to not over-fertilize. For instance, woody trees and shrubs do not need to be fertilized at planting time and older trees may get all the nutrients they need from fertilizer applied to neighboring lawns and plants. .If symptoms of nitrogen deficiency (yellow newer leaves) do appear, apply no more than .25 lb/actual nitrogen per inch of trunk circumference. Leaching salts out of saline soils (applying water over what may be a few hours very slowly so it can drain salt build-up below the roots) may be necessary to avoid damage to your plants.
Take Care of Your Trees. Trees are likely the most highly valued plants in your landscape. They provide shade, reduce temperatures in hot urban heat islands, add beauty, and even help clean the environment by storing carbon dioxide. Prune trees correctly.
Don't top trees! Topping a tree is the process of giving a tree a virtual crewcut by making one or more horizontal cuts across the top of the tree (add photo) to shorten it. Why is topping trees harmful? Topping trees results in unstable, unsafe, and unattractive trees. It also reduces the ability for trees to reduce high temperatures and provide adequate shade in urban heat islands, sequester (store) carbon produced by fossil fuels, and provide wildlife habitat. In some cases, trees are topped because a tall tree that should not have been selected in the first place is growing into utility lines. In other cases, topping occurs due to a lack of knowledge about the dangers of topping and/or simply wanting to save money by going with the lowest bid. In all cases, topping should be avoided. The combination of improper balance and weak, poor-quality growth following topping creates a much higher likelihood of personal injury and property damage than occurs from properly pruned trees.
Trees should be properly thinned and pruned rather than topped. Proper pruning involves maintaining the natural integrity and balance of the tree. (For detailed information on proper pruning visit the International Society of Arboriculture's (ISA) consumer website: www.treesaregood.org). Contact a Certified Arborist (https://www.isa-arbor.com/Credentials.) who is trained in tree health and care if you are in doubt about caring for your landscape trees. S/he will determine the proper pruning and thinning procedures and otherwise assess the overall health of your tree.
Prevent Circled and Kinked Tree Roots. Circled, kinked tree roots can lead to stressed trees that drop limbs or topple, causing injury to people and structures. They occur when trees are left too long in containers, are planted in too small of a planting hole, or when the planting hole is filled with organic matter such as compost. In the latter case, roots will often prefer the higher quality compost to the surrounding native soil and never grow beyond its bounds. In some cases, one or more condition exists. To avoid these problems, make sure roots are not overgrown at the time of purchase and do not add soil amendments to the planting hole.
Avoid Mechanical Injury to Tree Trunks. Remove staking ties before they cut off the flow of water and nutrients in the vascular system of the trunk. If the tree will not support itself due to high winds, loosen the ties and move outward any stakes that may rub the trunk as the tree grows. Add mulch around trees (but avoid contact with trunks) to prevent damage from mowers and weed trimmers. (Mulch also reduces soil evaporation and weed seed germination).
Avoid Soil Grade Changes. Grade changes from construction activities should be kept several yards from trees. Even small changes in the depth of the soil can result in serious root system injury. As little as four to six inches of soil applied on top of the root zone of a mature tree can dramatically reduce the amount of oxygen available to roots and can kill a tree over time. Lowering the grade can cause lower trunk and root injury and reduce the nutrient and moisture supply to the roots.