Tree
Chaste Tree
Vitex agnus-castus · Lamiaceae
Also called: Vitex, Monk's Pepper, Lilac Chaste Tree
Chaste Tree (Vitex agnus-castus) is a low-water tree well suited to Tucson and the low desert. It thrives in full sun, with a moderate to fast growth rate.
Chaste Tree at a glance
- Water use
- Low (established)
- Sun
- Full sun (best bloom); tolerates light shade with reduced flowering.
- Mature size
- 10-20 ft tall and wide (often grown as large shrub or small multi-trunk tree)
- Growth rate
- Moderate to fast
- Bloom
- Lavender-blue to purple (also white and pink cultivars) fragrant flower spikes, Late spring through summer (May-September), heaviest in early summer with repeat flushes
- Cold hardiness
- Cold hardy to about 5-10°F; root-hardy even if top is frost-nipped. Deciduous in Tucson winters; no frost protection needed.
- Soil
- Adaptable; prefers well-drained soil but tolerates a range of desert soils including alkaline. Needs good drainage to avoid root rot.
- Native range
- Mediterranean region and western/central Asia
- Best used as
- Flowering accent/specimen, Pollinator garden, Large shrub or small patio tree, Screen, Low-water color
- Wildlife
- Excellent pollinator plant: summer flower spikes are a magnet for honeybees, native bees, and butterflies; seeds attract some birds.
- Toxicity
- Considered low toxicity / generally non-toxic to people and pets; berries (monk's pepper) are used as an herb/supplement. Safe choice for family landscapes.
How to grow Chaste Tree in Tucson & the low desert
Watering
Drought tolerant once established; deep soak every 7-14 days in summer for best bloom, every 3-4 weeks in winter when deciduous. Tolerates more water than many desert plants but does not need it.
Fertilizer & nutrients
Light feeder; apply a balanced or slow-release fertilizer in early spring to support flowering. Generally low nutrient demand in desert soils; micronutrients rarely needed.
Pruning & care
Blooms on new growth, so prune in late winter while dormant; can be cut back hard to rejuvenate or shaped into a multi-trunk small tree or large shrub. Deadheading spent spikes in summer encourages repeat bloom.
Notes
Tough, heat-loving deciduous large shrub/small tree prized for showy summer lavender-blue flower spikes when little else blooms in Tucson's heat. Multi-trunk forms make attractive patio trees. Reliable, low-maintenance, and pollinator-friendly. Plant in spring or fall.
Sources: University of Arizona Cooperative Extension / Pima County Master Gardeners; AMWUA Landscape Plants for the Arizona Desert; Arizona-Sonora Desert Museum