Updated: Sep 22, 2021
What's not to love about Lagerstroemia indica, or crape myrtles? Right about now, mid to late summer, their ubiquity is obvious along streets, in parking lots, gardens, and parks. When we think of pops of colors from trees, spring blooms come to mind, but crape myrtles defy that urge and wait for just when that extra burst of show is needed while we are all outdoors enjoying the season. Their colors are festive; aside from newer cultivars in deep red, the others are what I associate with spring: pinks, lavenders, and white.
Their uses are diverse because of their tolerances and growth habits. They can handle most of California's heat quite well, and average soils with good drainage. New dwarf cultivars offer opportunities to use them as deciduous shrubs. Nurseries offer them in multi-trunk or standard forms, furthering the diversity of mature sizes. Shade trees, specimens, and accents are common uses, but they are also popular choices when designing roof terraces or green stormwater infrastructure systems. Should I go on with their other desirable qualities? Okay, let's go!
After their blooms are finished and autumn is upon us, most cultivars will turn brilliant yellows, oranges and/or red. Unlike other seasonal trees, such as maples, L. indica has fall color that can withstand California's hot Diablo or Santa Ana winds of autumn without looking too faded or withered. When the winter blahs hit, their multi-colored bark offers a bit of pizzazz, particularly if up lit during long winter nights. Have a convinced you of their awesomeness? Well, it is time to understand their drawbacks.
Numerous sources, including those listed below, discuss crape myrtle's vulnerability to powdery mildew, and if uncontrolled, will pollute all that striking Autumn color I referenced earlier. The local Mercury News even posted a Q&A with a Master Gardener on how to address it. Powdery mildew, a disease that coats the leaves with a white film and often leads to distorted leaves, is common not only in California (particularly where fog regularly blows in) but anywhere humidity is a concern, such as in the southeastern United States. The University of Florida recommends a simple solution, plant mildew resistant cultivars that have hit the market, such as those with names honoring Native American/First People and other newer forms. Powdery mildew alone, however, should not deter the determined.
Consider their mess. Prolific bloomers will drop flowers in the summer. As with all deciduous species, leaves will fall onto outdoor furniture, patios and sidewalks. Seed capsules hang on for a long time, and if they are considered unsightly, will prompt fastidious gardeners to remove them. Leaving them will clutter next years blossoms, but they may also produce seeds. Birds love seeds. Seeds spread by birds. L. indica is considered invasive in other parts of the country, even globally, and here in California, Calflora's Taxon Report monitors rogue specimens that are finding their way into the landscape. Not yet a problem in California, and our droughts may be aiding their negligible spread. They may, however, reseed in well irrigated landscapes.
Still determined? Okay, then here's one more reason (there are others, but this post is getting too long). Since this tree is on everyone's A-list in popularity, L. indica is overplanted causing a concern for lagging species diversity, leading researches to recommend limiting their use (McPherson, Kotow, 2013). Cities like City of San José have learned that monocultures of any one species raise concerns about future problems with pest invasions that can wipe out an urban forest. Yale Scientific describes a quick history of what happened to the American Elm when overly relied upon in urban landscapes. While crape myrtles are currently only bothered by controllable pests (aphids) and diseases (powdery mildew), the real concern is when trees become further vulnerable and overly planted, making them targets in the future.
One remedy is to limit their numbers. For example, the City of San Jose will discourage their specification by landscape architects when proposed as street trees, along with other overly specified trees, Platanus acerifolia and Pistacia chinensis (Ch4-7). If landscape architects are working on public projects, it behooves them to check in with their city or county officials for preferred species. These restrictions or recommendations may not affect private projects.
If I can offer any conclusion, it holds true with any commitment to trees specified in landscapes. Take into consideration local species diversity (or the lack thereof), long-term performance, vulnerabilities, such as pests and diseases, space availability, and of course client interests before making such decisions. Are crape myrtles right for you and your client? There are plenty of online sources that can help you with that decision.
West Valley College Campus Location: Lagerstroemia indica
Administration (westerly lawn)
Long: 122° 0'40.00"W
Botanical Name: Lagerstroemia indica
Lagerstroemia: Honoree, merchant and naturalist Magnus von Lagerström.
Indica: Associated with India, although at the time, could also reference East Indies or China
Common Name: Crape myrtle (Patrick Breen of Oregon State University references "traditional Southern [United States] spelling" as crepe myrtle, which sometimes finds its way to West Coast growers and references.
Family Name: Lythraceae
Positioning: Fore- middle- or background pending mature size
Garden Themes: Pollinator, courtyard/patio, parks, winter, urban, rain
Uses: Street tree, informal hedge, specimen, container (check mature sizes), planters, bonsai, screen, buffer, green stormwater infrastructure
Type: Deciduous shrub or tree (multi-trunk or standard)
Form: Round, vase
Size: 25' tall and wide (standards); other sizes available by cultivar or multi-trunk
Outstanding Feature(s): Flower, autumn foliage, bark
Bark: Light gray, tan, red-brown, mottled, exfoliating
Shape: Ovate, obovate
Color: Dark to medium green (some cultivars with red/purple in summer) turning yellow, orange, and/or red in autumn
Surface: Smooth, glossy
Flower: Summer. Showy, long-lasting terminal panicle with ruffled flowers in white or shades of pink, red, or purple.
Fruit: Summer to autumn. Green capsules turning brown when mature.
cultural requirements, tolerances & problems
Sunset Zones: 7-10, 12-14, 18-21
USDA Zones: 7-9
Light: Full sun
WUCOLS SF Bay Area Hydro Zone: Low
Texture: Sand, loam, clay
Moisture Retention: Well-drained
pH: Very acidic to slightly alkaline
Tolerances: Drought, heat, deer, Texas root rot
Problems: The way people incorrectly prune them.
Branch Strength: Medium
Disease: Powdery mildew, sooty mold
citations & attributions
Barrat, J. (2018). "Crape myrtle trees aren’t native to the U.S., but hungry native birds still find them tasty." Smithsonian Institute, Washington D.C. Accessed on August 17, 2021, from https://www.si.edu/stories/crape-myrtle-trees-arent-native-us-birds-find-them-tasty.
Bayton, R. (2019). The Royal Horticultural Society's the Gardener's Botanical: An Encyclopedia of Latin Plant Names. London: Mitchell Beazley.
Breen, P. "Lagerstroemia indica." Oregon State University, Corvallis. Accessed on August 18, 2021, from https://landscapeplants.oregonstate.edu/plants/lagerstroemia-indica.
Community Forest Management Team (Rev. 2013). Tree Policy Manual and Recommended Best Practices. City of San Jose. Accessed on August 18, 2021, from https://www.sanjoseca.gov/home/showpublisheddocument/2520/636633198872030000.
Extension Gardener. "Lagerstroemia indica." North Carolina State University, Raleigh. Accessed on August 18, 2021, from https://plants.ces.ncsu.edu/plants/lagerstroemia-indica/.
Gilman, E.F., Watson, D.G. (1993). "Fact Sheet ST-342." University of Florida, Gainesville. Accessed on August 18, 2021, from http://hort.ufl.edu/trees/LAGINDA.pdf.
Hsin, C. (2009). "'Elm City': the Tragic Misnomer: The Loss of Elms on Hillhouse Avenue Provides Greater Lessons on the Dangers of Monoculture." Yale Scientific, New Haven. Accessed on August 18, 2021 from https://www.yalescientific.org/2009/10/%E2%80%9Celm-city%E2%80%9D-the-tragic-misnomer-the-loss-of-elms-on-hillhouse-avenue-provides-greater-lessons-on-the-dangers-of-monoculture/.
Institute of Food and Agricultural Sciences. "Crape Myrtles resistant to powdery mildew." University of Florida, Gainesville. Accessed on August 17, 2021, from http://blogs.ifas.ufl.edu/nassauco/2017/03/03/crape-myrtles-resistant-to-powdery-mildew/.
Invasive Species Compendium. "Lagerstroemia indica Datasheet." CAB International, Wallingford. Accessed on August 17, 2021, from https://www.cabi.org/isc/datasheet/29669.
Kirk-Ballard, H. (2020). "The great crape myrtle controversies." Louisiana State University Ag. Center, Baton Rouge. Accessed on August 17, 2021, from https://www.lsuagcenter.com/profiles/rbogren/articles/page1608734072627.
Norris Brenzel, K. (Ed.). (2012). The New Sunset Western Garden Book. New York: Time Home Entertainment, Inc.
McPherson, E.G., Kotow, L. (2013). A municipal forest report card: Results for California, USA. Urban Forestry & Urban Greening. (v. 12, pp 134-143). Accessed on August 18, 2021, from https://www.sciencedirect.com/science/article/abs/pii/S1618866713000058.
Plant Finder. "Lagerstroemia indica." Missouri Botanical Garden, St. Louis. Accessed on August 18, 2021, from http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=282496.
SelecTree. UFEI. "Lagerstroemia indica Tree Record." 1995-2021. Cal Poly State University, San Luis Obispo. Accessed on August 18, 2021, from https://selectree.calpoly.edu/tree-detail/790.
Taxon Report. "Lagerstroemia indica." CalFlora, Berkeley. Accessed on August 17, 2021, from https://www.calflora.org/app/taxon?crn=9354.
Water Use Classification of Landscape Species. "WUCOLS IV Plant List." University of California, Division of Agriculture and Natural Resources, Davis. Accessed on July 27, 2021.
All photos by TELCS.