Desert Cassia: Evergreen Yellow-Blooming Shrub for Phoenix Landscapes

Desert Cassia (Senna artemisioides subsp. filifolia) is a tough, evergreen shrub from the dry interior of Australia that brings bright golden-yellow flowers to Phoenix landscapes with very little care. Its fine, needle-like, deep green leaves stay on all year, giving a lush look on very little water, and a profusion of yellow pea-like blooms covers the plant from late winter through spring. With extreme drought tolerance, a naturally rounded form, and cold hardiness to about 15°F, Desert Cassia is a go-to choice for water-wise gardeners in Phoenix, Scottsdale, and Mesa who want dependable cool-season color and year-round green structure.

Why Desert Cassia Thrives in the Phoenix Valley

Desert Cassia comes from the arid interior of Australia, where hot summers, poor rocky soils, and long droughts are normal, so it handles Phoenix's climate with ease. It blooms in late winter and spring, when its bright yellow flowers feed bees and brighten the yard ahead of the summer heat. It sets next year's flower buds in late summer and holds its deep green, needle-like foliage right through the year, so the shrub never looks bare. Gardens in Tempe, Gilbert, and Chandler use Desert Cassia as a dependable evergreen backbone that pairs well with Sonoran natives.

Landscape Uses

Desert Cassia works beautifully as a flowering accent, informal screen, or mass planting in xeriscape gardens. Its rounded form and deep green foliage pair well with boulders, decomposed granite, and gravel mulches, and make a good background that sets off gray and silver plants. Use it as a mid-border shrub, a low-water screen, or a colorful companion to desert natives like fairy duster, brittlebush, and globe mallow. Its late winter and spring bloom adds color before most summer bloomers get going.

Planting Density Guide

For naturalistic plantings, space Desert Cassia 4–5 feet on center to allow for its full mature spread. In wildlife garden designs, groupings of 3–5 plants spaced 4 feet apart create a dense pollinator hub. As a specimen shrub, allow 4–5 feet of clearance on all sides.

Best Time to Plant

Plant Desert Cassia in fall (October–November) or early spring (February–March). Fall planting gives roots the entire cool season to establish before summer heat and flowering demands. Container plants from Three Timbers can be planted spring through fall with appropriate establishment irrigation.

How to Plant Desert Cassia

1. Select a full-sun location with good drainage — this shrub comes from rocky, fast-draining soils in arid Australia.
2. Dig a hole twice the width of the container and the same depth as the root ball.
3. If a hard caliche layer is present, break through it to improve drainage.
4. Remove the plant from its container; gently loosen circling roots.
5. Set the crown at or slightly above grade.
6. Backfill with native soil — no amendments needed for this desert-adapted shrub.
7. Water deeply immediately after planting.
8. Apply 2–3 inches of decomposed granite mulch, keeping it away from the base of the stems.

Watering Guide

Watering Schedule

During the first 60–90 days, water on a tapering schedule: every 1 to 2 days for the first two weeks in summer (every 3 to 4 days in cooler months), every 3 to 6 days in weeks 3 to 6, and about every 7 days in summer (10 to 14 days in cooler months) by weeks 7 and 8, then keep stretching the interval. Once established (typically one growing season), Desert Cassia needs only occasional deep watering. Mature plants are among the most drought-tolerant shrubs available: they survive on very little supplemental water, but a deep soak every few weeks in summer keeps them fuller and flowering better.

Drip Irrigation Setup

Place a 1 GPH emitter 12 inches from the base of the plant. Run drip for 45–60 minutes per session, following the tapering establishment schedule above. Once established, reduce to a deep soak every 3 to 4 weeks in summer and skip irrigation after soaking monsoon rains. Avoid overwatering in winter, which leads to leggy growth.

Frequently Asked Questions

Is Desert Cassia native to Arizona?
No. The Desert Cassia we sell, Senna artemisioides subsp. filifolia, is native to arid inland Australia. It is a different plant from Arizona's native sennas, but it is fully adapted to the Phoenix Valley's heat, poor soils, and low rainfall, and its flowers feed local bees.

When does it bloom?
Desert Cassia blooms from late winter through spring, typically February through April, with a profusion of bright yellow pea-like flowers. It sets its flower buds in late summer, so prune right after bloom rather than in fall.

Does it attract pollinators?
Yes. Its bright yellow flowers draw bees, and birds pick at the seeds. Blooming in late winter and spring, it offers early-season forage when many summer bloomers are still resting.

Will it lose its leaves in winter?
No. Desert Cassia is evergreen and keeps its deep green, needle-like foliage year-round in the Phoenix Valley. A rare hard freeze below about 15°F can damage it, but established plants usually regrow from the roots.

Does it need pruning?
Light shaping right after flowering in spring keeps a tidy form and cuts down on seed pods. Avoid frequent shearing and fall pruning, since the plant sets next year's flower buds in late summer.

You May Also Like

Explore these complementary native and low-water plants at Three Timbers: Yellow Bells for bright yellow trumpet flowers that echo Desert Cassia's color, Autumn Sage Furman's Red for a contrasting warm red flowering accent, and Brake Lights Hesperaloe for a bold coral-red companion whose spring bloom overlaps Desert Cassia's.

How Many Desert Cassia Do I Need?

Desert Cassia matures around 4 to 6 feet wide, so space plants about 4 feet apart for a naturalistic mass or pollinator drift. Use this table to estimate counts:

For a dense pollinator hub, plant in odd-numbered groups of 3 to 5 spaced 4 feet apart. As a single specimen, give it 4 to 5 feet of clearance on all sides.

Desert Cassia Season-by-Season in Phoenix

• Spring (Feb to Apr): Peak bloom. Bright golden flowers cover the evergreen foliage and feed early bees. Prune lightly right after flowering ends. A good second planting window.
• Summer (May to Sep): Green and resting through the heat while seed pods ripen. Loves the heat and reflected heat on very little water. Next year's flower buds form in late summer, so skip pruning.
• Fall (Oct to Nov): Prime planting season for strong root establishment. Flower buds are set and the foliage stays deep green.
• Winter (Dec to Jan): Evergreen through Valley winters, with the first yellow blooms opening by late winter. Hardy to about 15°F, so it easily clears normal Valley frost.

At a Glance

✔ Evergreen   ✔ Pollinator-Friendly   ✔ Heat-Loving (Reflected-Heat Tolerant)   ✔ Drought-Tolerant   ✔ Low-Maintenance   ✔ Cold-Hardy to 15°F

Plant It With

• Yellow Bells: a hummingbird magnet with matching yellow blooms that pick up after the cassia's spring show.
• Autumn Sage Furman's Red: warm red flowers that contrast with the golden cassia bloom.
• Brittlebush: a Sonoran native with yellow spring daisies that bloom alongside the cassia.
• Desert Bird of Paradise: a taller yellow bloomer that anchors the back of a low-water bed.

Is Desert Cassia Right for Your Yard?

It is a great fit for xeriscape gardens that want late winter and spring color plus year-round green in full sun with very little water once established. It needs fast-draining soil with caliche broken through, and rewards a hands-off approach. Not a fit for rich, frequently watered beds, where too much water makes it leggy, or for a spot that needs summer flowers.