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Tree Guide

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Holly OakQuercus ilex

  • Northern Red Oak - Quercus rubra
  • Holly Oak Tree
The holly oak is a tough evergreen tree as wide as it is tall with a dense rounded crown. It has smooth gray bark. The leaves are a leathery, glossy, dark green and vary in size and shape. The margins may or may not be irregularly toothed. Acorns are produced in the first year falling in autumn. Holly oak tolerates a wide variety of soil textures, salt, and drought, but is sensitive to cold. It requires regular watering until it is established and then should not be overwatered as this invites powdery mildew. Be sure to keep irrigation away from the base of the trunk as root rot can set in. It may require pruning when young to develop a strong branch structure. If left unpruned it can develop multiple leaders and take on a large shrub form. When given adequate soil space, it does well along streets and parking lots, and in parks and gardens in the western United States.

Hardiness Zones

The holly oak can be expected to grow in Hardiness Zones 0–0. View Map

Tree Type

Mature Size

The holly oak grows to a height of 40–70' and a spread of 50–60' at maturity.

Growth Speed Slow to Medium Growth Rate

This tree grows at a slow to medium rate, with height increases of anywhere from less than 12" to 24" per year.

Sun Preference

Full sun is the ideal condition for this tree, meaning it should get at least six hours of direct, unfiltered sunlight each day.

Soil Preference

The holly oak tolerates a wide range of soil textures from acidic to slightly alkaline. It can also tolerate drought (once established) and salt.

Attributes

This tree:
  • Features simple, leathery, glossy dark green leaves that are 1–3" long with spine-tipped teeth along the margin, although some are untoothed. They have a stiff, holly-like texture.
  • Yields 1" round acorns that are greenish-yellow and brown and mature in the first year, dropping in the autumn.
  • Tolerates drought and salt.
  • Produces drooping catkins in the spring as it leafs out.
  • Grows in a rounded shape.
  • Is sensitive to cold.
  • Should not be overwatered once established, as this invites powdery mildew.
  • May require pruning when young to develop a strong branch structure.

Wildlife Value

Birds and squirrels are attracted to the holly oak for food and shelter.

History/Lore

The holly oak is native to the Mediterranean region. The range is from Spain along the Mediterranean fringe east toward western Pakistan. Other common names are Holm oak and evergreen oak. In the foothills of the Spanish Pyrenees, black truffles are grown on the roots of these trees.