Tree
Holly Oak
Quercus ilex · Fagaceae
Also called: Holm Oak, Evergreen Oak
Holly Oak (Quercus ilex) is a moderate-water tree well suited to Tucson and the low desert. It thrives in full sun, with a slow to moderate growth rate.
Holly Oak at a glance
- Water use
- Moderate (established)
- Sun
- Full sun
- Mature size
- Typically 30-50 ft tall and 30-50 ft wide in the low desert; slow to develop a dense, rounded evergreen canopy.
- Growth rate
- Slow to moderate
- Bloom
- Yellowish-green (catkins; not ornamentally significant), Spring (inconspicuous catkins)
- Cold hardiness
- Cold-hardy in Tucson; tolerates temperatures into the low teens (F), well below typical USDA 9a/9b lows. No frost protection needed.
- Soil
- Adaptable; tolerates Tucson's alkaline, rocky, low-organic soils but requires good drainage. Avoid heavy, poorly drained spots.
- Native range
- Mediterranean region (southern Europe, North Africa)
- Best used as
- Shade tree, Evergreen screen, Street/median tree, Specimen/large lawn tree
- Wildlife
- Acorns provide food for wildlife and birds; dense evergreen canopy offers nesting and roosting cover.
- Toxicity
- Acorns and foliage contain tannins and can be toxic to livestock (horses, cattle) if eaten in quantity; not a significant hazard to typical household pets or children but acorns are not for consumption.
How to grow Holly Oak in Tucson & the low desert
Watering
Water deeply and infrequently to a depth of 2-3 ft, letting the top several inches dry between irrigations. Established trees need deep soakings roughly every 2-3 weeks in summer, monthly or less in winter; deeper, less frequent water encourages a strong root system and drought tolerance.
Fertilizer & nutrients
Generally low feeders; mature desert specimens rarely need fertilizer. If foliage yellows (chlorosis from alkaline soil), apply a chelated iron supplement and a light spring application of a balanced or slow-release nitrogen fertilizer.
Pruning & care
Prune in late winter or early spring to remove dead, crossing, or weak branches and to establish a single strong leader and good scaffold structure while young. Avoid heavy summer pruning that exposes bark to sunscald.
Notes
A durable, drought-tolerant evergreen oak well suited to Tucson once established; tolerates heat, alkaline soils, and reflected light. Slower-growing than many desert trees, which makes it long-lived and low-maintenance. Provide adequate root space for its eventual size and stake young trees only as needed.
Sources: University of Arizona Cooperative Extension; Arizona-Sonora Desert Museum; AMWUA Landscape Plants for the Arizona Desert