Renovation for a Sustainable Future: Caltech Campus Frontage on Wilson Avenue

Wilson Avenue defines the western edge of Caltech's historic campus. Its original landscape consisted of wide sweeps of lawn dotted with a few shade and accent trees.

Caltech has reconceptualized the plantings for this area to carry forward its historic beauty while adapting to current conditions. The new landscaping increases the tree canopy and shade, protects against the impacts of extreme weather, reduces fire risk, enhances pollinator habitat, and readies Caltech for a law that will prohibit using potable water to irrigate nonfunctional turf on nonresidential properties. The Metropolitan Water District of Southern California has provided essential partnership, guidance, and a turf-replacement rebate.

This renovation maintains the traditional sweep of open ground planes and sightlines for pedestrians and passersby, accenting campus entry corridors, complementing building facades, and shading walkways. The plan enhances tree canopies and replaces turf grass with drifts of low groundcovers. Campus entrances are marked with distinctive plantings.

Notably, the entrance of the east-west axis of the original campus is marked by formal arrangements of iconic native Engelmann oaks and exotic Hercules Tree Aloes, recalling the work of the designer-architect Bertram Goodhue and his view of developing a beautiful campus.

Recognizing the increasing effects of extreme weather, especially temperature fluctuations due to climate change, large-scale tree canopies provide cooling through shade and by reducing reflected heat and light and heat gain on paving and buildings. To capture runoff and contribute to groundwater storage, regraded contours add storm water retention and infiltration swales.

The planting palette consists of Southern California native and Southern California heritage plant materials. Keystone indigenous species include long-lasting, large-scale Engelmann, Valley, and California live oaks (Quercus engelmannii, Quercus lobata, Quercus agrifolia).

The design enhances habitat for native fauna, especially pollinators, and also includes extremely drought and heat adapted species such as Netleaf oak (Quercus rugosa), native to the American Southwest and northern Mexico. This species has been identified as exceptionally climate resilient and a valuable habitat species for coastal California.

Southern California native plants in the understory are known for their abilities to reseed and thrive without extra or specialized maintenance. They provide habitat and successive blossoms over the seasons:

Spring

• Dara's Choice sage (Salvia ‘Dara's Choice')

Spring and summer

• Blue Bedder (Penstemon heterophyllus ‘Margarita BOP')
• Cedros Island verbena (Verbena lilacina ‘De La Mina')
• Island pink yarrow (Achillea millefolium ‘Island Pink')
• Santa Ana Cardinal coral bells (Heuchera ‘Santa Ana Cardinal')

Summer

• California Buckwheat (Eriogonum fasciculatum ‘Warriner Lytle')

Summer and fall

• Everett's Choice California Fuchsia (Epilobium canum ‘Everett's Choice')

Heritage plants of the Pasadena region have been found to be exceptionally enduring, resilient, resource conserving, low maintenance, and drought adapted on the Caltech campus, and are part of the historical fabric of the Caltech landscape. They have been proven over decades in multiple settings to be noninvasive yet horticulturally adapted, resilient plants for this region.

• Ginkgo trees, an ancient genus able to survive drought, flooding, high winds, and more
• Dwarf Abelia (Abelia x grandiflora ‘Sherwoodii'), an evergreen, very-long-lived selection
• Bearberry Cotoneaster (Cotoneaster dammeri ‘Lowfast')
• Lantana (L. montevidensis ‘Alba' and ‘Spreading Sunset')
• Prostrate rosemary (Rosmarinus officinalis ‘Huntington Carpet')
• Fortnight lily (Dietes grandiflora ‘Sun Stripe')
• Dwarf mock orange (Pittosporum tobira ‘Cream de Mint')
• Dwarf Yeddo hawthorn (Rhaphiolepis umbellata ‘Minor')

Historically, campus succulents were agaves whose rosettes die after flowering. The new landscape design continues to include succulents as extremely drought adapted and fire resistant species. The Agave genus is replaced by long-lasting, long-flowering Aloe, which are a valuable food source for many birds, especially hummingbirds and orioles. Aloe species were selected to provide successive bloom throughout the seasons.

Selection of proper Southern California native and heritage plants and their careful placement was important to reduce community fire risk vulnerability while supporting campus biodiversity and wildlife and maintaining aesthetic integrity. Quercus, Ginkgo, Lantana, Pittosporum, Salvia, Verbena lilacina, Cotoneaster groundcovers, Rosmarinus, Epilobium, Penstemon, and Heuchera are all listed by CAL FIRE as fire resistant genus/species. With their high-moisture and ignition resistance, Aloes are designated fire-retardant by many California fire departments.

The new design for the western edge of campus sustains the tradition of a remarkably beautiful campus while ushering in a modern, resilient plant palette and landscape features that enhance biodiversity and safety while conserving water and energy.