Posts Tagged: trees
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>
• Your trees come first! If there just isn't enough water to go around, your lawn and flowers should be sacrificed instead. Trees are our most valuable landscape resource and take years to maximize their benefits (shade, cooling, habitat/ecosystem enhancement, carbon dioxide storage, etc.).
• Spread and maintain 2-4” of mulch around garden plants and trees (3-4” for wood chips, 2” for pebbles, decomposed gravel, etc.) keeping it a few inches away from tree trunks.
• Water early in the morning when soil evaporation is minimal.
• Control weeds. They compete with other plants for water.
• Avoid fertilizing. Nitrogen increases growth and the need for more water.
• Don't plant new plants during the summer when temperatures are highest. Even drought-resistant native and non-native plants need regular watering their first season.
During the drought, your trees should come first! Because many well-maintained trees don't reach their prime until their 4th or 5th decade, it's important to keep them watered during the drought and water restrictions. Older trees absorb higher levels of carbon dioxide, do a better job of cooling urban heat islands and providing shade. They also filter air and water pollutants, reduce soil and water erosion, provide habitat for wildlife, enhance privacy, beautify neighborhoods and parks, enhance property values, and even improve mental and emotional health. Trees are worth saving! The price of starting over is just too steep.
Recognizing early signs of drought stress is important because irreversible damage can occur that no amount of watering will correct. If you cash in your grass for a water district rebate, remember to water any trees that relied on water from the lawn sprinklers. This is because tree roots grow laterally quite a distance, often well beyond the dripline of the tree under the lawn. Over time, start watering them more deeply and less often to encourage deeper roots and enhanced stability.
Just a few deep waterings in mornings or late evenings with a garden hose during spring and summer can keep a tree alive, even during a drought. Keep the trunk dry and water from the mid-dripline outward. Apply a slow steady stream of water, moving the hose to another section of the tree every 1-2 hours. Another inexpensive way to water your trees is to encircle them with soaker hoses that connect to a garden hose. The soaker hose should be in concentric rings about one foot apart starting two feet away from the trunk for a larger tree, closer for a more recently planted tree with a more confined root system.
Check trees regularly for these common symptoms of water stress:
• Wilting or drooping leaves that don't return to normal by evening
• Yellow, brown or sometimes gray leaves that may drop from the tree
• Small new foliage and stunted overall tree growth
Other ways to reduce tree water loss include:
• Keep weeds out (they compete for water
• Maintain a 3-4” of organic mulch or 2” layer of inorganic mulch (pebbles, decomposed gravel) around your trees, starting a few inches away from the trunk outward.
• Avoid fertilizing since that increases their water need.
• Do only necessary pruning (to remove dead wood and any dangerous limbs that look like they might fail) since this stresses the tree and can increase its water need.
UC Resources at Your Fingertips:
Free Download Publications: https://anrcatalog.ucanr.edu
-Keeping Plants Alive Under Drought and Water Restrictions
-Sustainable Landscaping in California
-Lawn Watering Guide for California
-Use of Graywater in CA Landscapes -
CA Institute for Water Resources: http://ciwr.ucanr.edu/ (blogs, climate-smart ag, podcasts, etc.)
UC Cooperative Extension Master Gardener Program:
For more drought tips and help with your home gardening questions, contact a UCCE Master Gardener volunteer. Find your local program atucanr.edu/FindUs/
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. Irrigate the tree immediately after planting through the entire root system and slightly deeper. Keep in mind that soils with appreciable clay content absorb water more slowly than sandier soils and need to be watered longer but less often. Water newly planted container trees often through their establishment period, even if they are drought tolerant 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. (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 firstname.lastname@example.org
Our population of urban trees is shrinking! You can help turn this around by protecting your own trees and by planting new ones recommended for your climate and the conditions around your home. For more on this topic, please revisit my February blog for specific selection and care recommendations: https://ucanr.edu/b/~ZuB.
In addition, please encourage your city to plant a wide range of recommended species today for a healthier tomorrow. Why is this so important? Many of our current street trees are in the 11th hour of their lifespans. While some that were planted decades ago are simply aging naturally, in other cases, they are perishing prematurely due to poor selection and care. This leads to a downward spiral; trees not adapted to the climate they're planted in and not receiving proper care are much more susceptible to invasive pests (shot-hole borers, etc.) and diseases than are healthy, well- chosen and maintained trees. Even the loss of one front yard shade tree can significantly reduce shade, increase the surrounding temperature, and diminish energy savings.
Another reason we're losing our trees is due to the negative impacts of urban heat islands (UHIs) which shorten the lifespan of many species of trees dramatically. Some trees (even many natives!) just aren't able to withstand the higher temperatures (sometimes exceeding 20 degrees) they are subjected to due to UHIs.
What are urban heat islands and why should we care? Urban heat islands are caused by reradiated heat from paved concrete and (especially) asphalt surfaces.
And, our cities are growing and expanding. Very few Southern California residents reside in rural areas. Instead of living near pastures, field-filled crops, and forests that cool the surrounding area through evapotranspiration, the vast majority of us reside in warmer urban city centers. Conditions we expect our city trees to endure in 2021 are very different from even 20 to 30 years alone, let alone decades ago.
The good news is that, through proper tree selection and care, we can be a part of the solution. In fact, trees offer many benefits that offset the impacts of UHIs. Cities with larger tree canopies are a testament to this fact and have fewer adverse impacts from UHIs than do cities with low tree canopies. Trees reduce the impact of UHIs by shading parking lots, buildings, and vehicles), deflecting the sun's radiation, and cooling the atmosphere through evapotranspiration. Trees also absorb and store carbon which lessens the impacts of pollution from fossil fuels. A well-tended mature landscape tree can absorb 40 tons of carbon over its lifespan.
The solution? Augment our current urban tree palettes with heat, drought, and pest-resistant native and adapted non-native species. A case in point of a native tree in trouble is our beautiful Joshua trees (Yucca brevifolia) which are dying off in their namesake National Park and seeding 500 or more feet higher elevation than parent plants. Planting trees that withstand UHIs today is crucial for tomorrow.
We are well on the way to identifying landscape tree species that can remain healthy under adverse urban conditions. In our study examining the performance of 12 species of underplanted but promising landscape trees, several candidates are standing out for their heat, drought, and pest resistance.