Invasive Shade-Tolerant Garden Plants in Arizona

Introduction

Arizona’s unique landscapes, from its desert environments to riparian zones, are under threat from several shade-tolerant garden plants that have become invasive. Often introduced for landscaping, these plants can spread rapidly in shaded areas, outcompeting native species and disrupting natural habitats. Understanding these invasive species and opting for native alternatives is crucial for preserving Arizona’s natural beauty and ecological balance.

List of Invasive Shade-Tolerant Garden Plants in Arizona

1. Tree of Heaven (Ailanthus altissima)

• Description: The Tree of Heaven is a fast-growing deciduous tree with large compound leaves and clusters of yellow-green flowers. It’s commonly planted in urban and suburban areas because it is resilient, even in shaded environments.

• Impact: This tree forms dense stands that outcompete native vegetation and releases allelopathic chemicals that inhibit the growth of other plants. It can rapidly invade forested and riparian areas, altering ecosystems and reducing biodiversity.

• Garden Alternative: Velvet Mesquite (Prosopis velutina) - A native tree that provides shade and supports local wildlife without the invasive tendencies.

2. Russian Olive (Elaeagnus angustifolia)

• Description: Russian Olive is a deciduous tree or large shrub with silvery leaves and yellow, fragrant flowers. It’s often found in shaded riparian zones and along streambanks.

• Impact: This plant invades riparian areas, displacing native vegetation, altering soil chemistry by fixing nitrogen, and reducing habitat quality for wildlife.

• Garden Alternative: Arizona Sycamore (Platanus wrightii) - A native tree that provides ample shade and supports riparian ecosystems.

3. Tamarisk (Saltcedar) (Tamarix spp.)

• Description: Tamarisk is a deciduous shrub or small tree with slender branches and small, scale-like leaves. It’s commonly found in shaded areas near water sources.

• Impact: Tamarisk consumes large amounts of water, outcompetes native plants, and increases soil salinity, which can degrade habitats for native species.

• Garden Alternative: Desert Willow (Chilopsis linearis) - A native tree with beautiful flowers that is well-suited to riparian areas and provides shade.

4. Fountain Grass (Pennisetum setaceum)

• Description: Fountain Grass is a tall, clumping grass with long, narrow leaves and fluffy flower spikes, often used in landscaping for its ornamental appeal in shaded areas.

• Impact: This grass spreads rapidly into natural areas, outcompeting native plants and increasing the risk of wildfires due to its dry, flammable biomass.

• Garden Alternative: Blue Grama (Bouteloua gracilis) - A native grass that provides similar ornamental value without the invasive potential.

5. Periwinkle (Vinca major and Vinca minor)

• Description: Periwinkle is a trailing evergreen ground cover with glossy leaves and blue or purple flowers, often used in shaded garden areas.

• Impact: It spreads aggressively, forming dense mats that crowd out native vegetation, particularly in riparian and forested areas.

• Garden Alternative: Parry’s Penstemon (Penstemon parryi) - A native ground cover with vibrant flowers that thrives in shade without becoming invasive.

Conclusion

While these plants are popular for shaded garden areas in Arizona, their invasive tendencies can significantly harm natural ecosystems. By choosing native, non-invasive alternatives, you can help maintain Arizona's ecological balance, support local wildlife, and preserve the state’s natural beauty.