The Importance of Trees

A top Altadena Heritage priority is to increase the urban forest and its cooling canopy in our town.
Welcome to our Tree Page with information on selecting, planting, caring for and maintaining your trees. A top Altadena Heritage priority is to increase the urban forest and its cooling canopy in our town.

This effort has been supported for several years by Southern California Edison.

Learn to Select, Plant and Care for Your Trees

We have reached out to tree experts to help us provide a series of workshops and additional information to help residents make the right decisions about choosing, planting and caring for the best trees that suit our climate and contribute most to the cooling and improvement of our environment.

Tree Workshops

Led by tree expert and plant pathologist, Dr. Jerrold Turney

Right Tree, Right Place – Tree Selection and Siting

Pruning and
Tree Care

A Tree Planting Demonstration

Trees NOT to Plant in Southern California – and Why

The following list of trees should not be planted in Southern California due to widespread lethal tree diseases that have no effective treatment. The pests/diseases that are of greatest concern are Bacterial Leaf Scorch and Invasive Shot Hole Bore.

Bacterial Leaf Scorch

Bacterial Leaf Scorch has been present in California for more than 100 years. In 1990 Oleanders started dying and were diagnosed as infected with Xylella fastidiosa in 1993. Soon thereafter Liquidambar styraciflua, Plums, Crape Myrtle and Olive were observed dying and diagnosed as infected with Xylella fastidiosa. Xylella fastidiosa is the causal agent of Bacterial Leaf Scorch. These five hosts are now dying throughout Southern California. Any trees planted will likely die in 5-10 years and have no chance of reaching mature size before they die.

Trees NOT to plant due to Bacterial Leaf Scorch

  • Liquidambar
  • Olive
  • Plum (especially Purple Leaf Plum),
  • Crape Myrtle
  • Oleander

Invasive Shot Hole Borer (ISHB)

Invasive Shot Hole Borer (ISHB) was first found at Whittier Narrows in Los Angeles County in 2003 but was not identified until several years later.

From 2003-2010 the beetle was found on a few ornamental trees, then in 2010 it was the presumptive cause of the death of a large number of box elder street trees in Long Beach. In 2012 the beetle was collected from a backyard avocado tree in South Gate, and from several tree species at local botanical gardens. It now appears to be established in Los Angeles, Orange, and Riverside Counties and has also spread to selected areas of San Bernardino, Ventura and Santa Barbara Counties. A single beetle was caught in Santa Cruz County in 2014. 

The host list for ISHB is now over 60 different tree species. Some hosts are preferred hosts and others are less attractive to the beetle. Preferred hosts of ISHB should not be planted as they will likely die in 5-10 years and never reach mature size before dying. I have observed that all species of Acer (Maple) and Platanus racemosa (Western Sycamore) are highly susceptible and are dying throughout Southern California and should not be planted.

Trees NOT to Plants Due to Likely Death From ISHB
    • Acer buergerianum – Trident maple
    • Acer macrophyllum – Big leaf maple
    • Acer negundo – Box elder
    • Parkinsonia aculeata – Palo verde
    • Platanus racemosa – California sycamore
    • Platanus hispanica – London plane
    • Populus fremontii – Fremont cottonwood
    • Populus nigra – Black poplar
    • Populus trichocarpa – Black cottonwood
    • Quercus lobata – Valley oak
    • Quercus robur – English oak
    • Ricinus communis – Castorbean
    • Salix gooddingii – Black willow
    • Salix laevigata – Red willow
    • Salix lasiolepis – Arroyo willow

Jerrold Turney Ph.D.

Consultant in Plant Pathology and Arboriculture
ISA Certified Arborist #WC-2364
Pest Control Adviser License #75603

Tree Resources

Altadena Heritage has compiled the following list of online resources to learn more about trees – how to access, select, plant and care for them.

General Information

L.A. County Public Works Call 818-249-3094 or go to websiteto request a parkway tree.

SelecTree, Cal Poly San Luis Obispo – Website
Provides a wealth of information on any particular species of tree.

Tree PeopleWebsite
Very active in Los Angeles. This is a great website with lots of information about the Urban Forest, trees, gardening, how to get involved, etc. The DIY section is very good.

California ReLeaf – Website
Provides grants to communities for arbor day events and for large planting projects. They advocate for planting large trees, as those will have a larger impact on climate change and the urban heat island effect. Website has webinars, videos, slide show presentations, newsletter, links to many resources.

California Urban Forests Council –  Website

L.A. and Orange Counties Regional Urban Forests CouncilWebsite
Presentations of past seminars available here. Publishes a tree guide.

International Society of ArboricultureWebsite
Lots of advice for the tree owner, including how to buy a high-quality tree. Will help you find certified arborists in our area and check their credentials.

Urban Tree Foundation – Website
Research-based advice on tree buying, planting, and care for the professional and the homeowner. See especially this guide: PDF

Tree Care for Birds –  Website
Best management practices to protect birds and other wildlife during and beyond nesting season. Good resources page and some great photos.

Selecting the Right Tree

LADWP Home Tree Guide – Website

Tree People’s LA City Approved Tree List – click on plant lists – Website

Pasadena Cool Trees Guidebook (2018) – PDF

How to Choose the Right Tree for the Right Place – Website

The Large Tree Argument – PDF

Buying High Quality Trees – PDF

Selecting the Best Site

Pasadena Cool Trees Guidebook – PDF

LADWP Home Tree Guide – Website

Tree Planting & Care

CALFIRE Nursery Standards & Specs  – PDF

Planting to Protect Against Wildfire

With wild fires such a current issue for Altadena residents, here are some articles to help you plant and care for a more fire resistant landscape.

  • A Guide to Defensible Space – PDF & PDF
  • Very High Fire Severity Zone Map – Website
  • Ca Buildings in Fire Zones – Website
  • Pasadena Cool Trees Guidebook – PDF
  • LADWP Home Tree Guide – Website
  • Wildfire Safety Guide – Website

Fire Resistant Landscaping

Fire-safe Plant Lists

  • Diablo Firesfe – Website
  • Fire Safe County- PDF
  • Tuloume Firesafe –  PDF