- Author: Janet Hartin
Many previously “welcomed” urban tree species have outlived their stay, becoming invasive and crowding out other plants in our Southern California landscapes. You can help by avoiding planting these trees identified by various sources (including the California Invasive Plant Council) to be too aggressive and habitat/resource-depleting for further planting.
Invasive Trees to Avoid Planting
Athel (Tamarix aphylla)
Black Locust (Robinia pseudoacacia)
Blackwood Acacia (Acacia melanoxylon)
Brazilian Pepper (Schinus terebinthifolius)
Chinaberry (Melia azedarach)
Chinese Tallow Tree (Triadica sebifera)
English Hawthorn (Crataegus monogyna)
Peruvian Pepper Tree (Schinus molle)
Red Gum (Eucalyptus camaldulensis)
Russian Olive (Elaeagnus angustifolia)
Saltcedar (Tamarix ramosissima, T. gallica, T. chinensis)
Silver Wattle (Acacia dealbata)
Smallflower Tamarisk (Tamarix parviflora)
Tasmanian Bluegum (Eucalyptus globulus)
Plant These Instead
They are drought/heat resistant, low maintenance, and have no known significant pest or disease problems and are not currently overplanted). Find other suggestions here: https://www.cal-ipc.org/solutions/prevention/landscaping/dpp/?region=socal
African Fern Pine (Afrocarpus falcatus) (formerly Podocarpus elatior)
Cascolote (Caesalpinia cacalaco Smoothie®)
Desert Willow ‘Bubba' (Chilopsis linearis)
Fringe Tree (Chionanthus virginicus)
Island Oak (Quercus tomentella)
‘Maverick' Mesquite (Prosopis glandulosa)
Mulga (Acacia aneura)
Netleaf Hackberry (Celtis reticulata)
Pink Chitalpa (x Chitalpa tashkentensis 'Pink Dawn')
‘Red Push' Pistache (Pistacia x ‘Red Push')
Thornless South American Mesquite (Prosopis x Phoenix)
/span>- 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 with the right care, landscape trees can be enjoyed for 100 years or more. Landscape trees cool urban heat islands, absorb carbon dioxide, filter toxic chemicals from soil preventing them from polluting our waterways, reduce soil and water erosion, reduce internal energy needs and related costs, provide habitat, and beautify neighborhoods.
Spring is a much better times to plant a container landscape tree in California than is summer. Trees incur far less stress if they've been in the ground several weeks rather than having to immediately adapt to high summer temperatures. Cooler weather allows plants to establish roots in their new ‘home' before the harshness of summer sets in. (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 and micro-climate.
Choose trees based on your Sunset climate zone (more precise than USDA zones for California since they include impacts of high temperatures as well as low temperatures) and your microclimate (shade, soil conditions, space, etc.). Four of my favorite search engines that allow one to search by multiple criteria (size, water needs, flower color, ecosystem functions, pest susceptibility, etc.) are: Inland Valley Garden Planner: https://inlandvalleygardenplanner.org/; Cal Poly, Pomona: https://selectree.calpoly.edu;California Native Plant Society: http://www.cnps.org/cnps/grownative/lists.php; and WUCOLS IV (Water Use Classification of Landscape Species): http://ucanr.edu/sites/WUCOLS
Avoid circled, girdled roots. Remember to inspect the root system of container trees. Avoid purchasing 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.
Planting the tree. Dig a 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 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 taking trees tightly, restricting flex. As the tree matures, remember to loosen ties and aim for removing stakes entirely if the tree is 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.
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 San Bernardino County Master Gardener Helpline at mgsanbern@ucanr.edu
- Author: Janet Hartin
As 2020 comes to a close, I'd like to express my deep appreciation and thanks to all of our UCCE San Bernardino County Master Gardener volunteers who have given the ‘gift of their time' to provide credible information to the gardening public. Even during COVID, they've found creative and safe means to continue reaching the public by converting face-to-face classes and workshops to online opportunities.They've gone above and beyond their expected volunteerism by helping those in need during these difficult times by working with our partners to distribute free seeds, trees, and wattles (for erosion control) and ensuring a happy holiday season for children and adults in need through a gift drive. Through COVID, the UCCE Master Gardeners have maintained their email and phone helplines to help county residents solve their gardening quandaries (linked here) mgsanber@ucanr.edu and (909)387-2182.
Master Gardener volunteers helped thousands of county residents landscape more sustainably, grow food in home, community, and school gardens, and deepen their appreciation of nature. They:
- Taught classes on drought-resistant landscapes and growing food in home, school, and community gardens
- Hosted ‘Ask the Master Gardener' sessions
- Provided education to community and school gardeners
- Distributed gardening information and answered questions at Farmers' Markets, community fairs and other events
- Answered home gardening questions via email and phone helplines
- Shared gardening information through social media
- Helped promote planting trees to cool urban heat islands in underserved neighborhoods and communities
- Helped take research data on the 'trees for tomorrow' project
- Published the monthly Master Gardener newsletter (thanks Phoebe, Debbie, Maggie, Robin, Sue and contributing authors!)
A special ‘shout out' to our monthly 2020 ‘Spotlight' Master Gardener volunteers for their extraordinary service:
I'd also like to recognize our dozens of non-profit partners including Inland Empire Resource Conservation District and the County of San Bernardino.
And, last but far from least, I'm forever thankful to UCCE San Bernardino County Master Gardener Coordinator Maggie O'Neill whose passion, heart, and expertise keeps the program thriving!
Happy Holidays to All!
- Author: Janet Hartin
Most trees in California need supplemental irrigation above and beyond what Mother Nature supplies naturally. Even drought-resistant species need regular watering through their first growing season due to their shallow roots. Once trees become established, it's important to water less often but more deeply to encourage deep rooting and structural balance above and below ground. Both under and overwatering can lead to unhealthy trees and even death if the situation is not corrected. Trees receiving too little or too much water exhibit similar symptoms since, in both cases, water is not available to the plant. Trees initially wilt, grow slowly, and develop yellow leaves. Over time, growth stops and leaves become brown and drop. Overwatered trees often develop lower crown and root rot from one or more disease-forming pathogens.
Knowing what type of soil you have (soil texture) is as important as knowing the water needs of your trees. Use the ‘feel test' (pictured below) to find out how much water your soil holds and how often to water. Heavier clay-based soils hold water longer and drain more slowly than sandier soils that need to be watered more often for shorter periods of time.
Trees should not be watered on the same irrigation system used for lawns and groundcovers. Soaker hoses and drip systems allow trees to be watered less often but for longer periods of time than your lawn or groundcover. Avoid applying water too close to the trunk. Instead water half-way between the trunk and the dripline of the tree and outward. If you use a garden hose, apply the water on the lowest volume possible slowly, moving the hose every few hours to each of four quadrants around the tree.
Applying a 3-4 inch layer of mulch around the tree can reduce soil evaporation. Use only non-flammable mulches in fire-prone areas within five feet from the house and non-contiguous for the first 30' away from the house. In all cases keep mulch a few inches away from tree trunks to keep the trunks dry.
Tip: Before planting a tree, make sure there is adequate drainage. Dig a hole where you want to plant it (the same depth of the pot, which is about one foot) and fill the hole with water. Let it completely drain and refill it. Measure the time it takes to drain one inch using a ruler. If it does not drain more than one inch an hour it is not a good location for your tree. Avoid adding compost or soil amendments to try to correct the problem since tree roots will likely grow in circles, staying within the confines of the amended hole rather than growing outward the confines of the amended hole rather than growing outward.
- Author: Janet Hartin
On Friday UCCE San Bernardino County Master Gardener Coordinator Maggie O'Neill and I hosted a tour that showcased UC ANR Urban Water Use Specialist's Amir Haghverdi's landscape plots at the UCR Citrus Experiment Station. In attendance were CEO Scott Kania and Lead Scientist Mark Chandler from EarthWatch, Becky Rittenburg and Monica Curiel from Chino Basin Water Conservation District, and Darrel Jenerette, UC Riverside Professor of Landscape Ecology. Our team is implementing an exciting citizen science project measuring water conservation based on implementing 'best practices' in urban landscapes in the greater Los Angeles Basin.