Quercus ilex var. integrifolia holm oak, holly oak
size/type
taller shrub,medium-sized tree
usual height
4-10m
usual width
3-6m
leaves
evergreen broadleaf
colour of leaves
location
full sun
soil type
any (acidic to alkaline)
soil moisture requirements
dry and sharply drained (xeriscape)
USDA zone (lowest)
7 (down to -23°C)
winter protection
for zone 5+6
for zone 7
categorized
Holm oak or holly oak (holm is an old word for holly) is native to the Mediterranean and is spread from southern parts of Italy, France, Spain, and Portugal to west Balkan and milder parts of North Africa. In the past it occupied vast areas forming evergreen forests most of which are chopped down today. It was first described in 1753 and until this day many sources claim it is not drought tolerant. In fact, it very drought tolerant once established which is why it is commonly cultivated in heat-accumulated and paved city squares. In the wild it grows in altitudes from 0 to 1400 m above sea level.
Description of the plant:
Holm oakis a natural species, not a hybrid despite two specific names in its Latin title. Integrifolia is one of its few selections first described in 1836. Its evergreen, leathery leaves are spineless with less conspicuous notches or serration at margins, often with none whatsoever. They are 3-6 cm long, elongated, to narrowly ovate or lanceolate, and slightly undulated or curved downwards. They emerge soft green and mature to very dark green and glossy on the upper side, and delicately hairy and almost silver on the reverse. Older trees produce small, elongated to rounded, dark brown, glossy acorns.Young plants are fast growers making some 30 cm to one meter per year. They grow mostly upright when young, slowing down with age, forming handsome and bushy canopies which are initially oval-shaped and later dome-shaped or even mushroom-like which turns out best if cultivated as a multistemmed tree. Older trees are very beautiful and cast a deep shade so desired in hot summers. Shrubs are used as long-lived hedges and windbreaks.
We began testing this plant after 2010. Young plants with soft wood had no chance to survive the first winter outside (-24 °C), but trees with older and woody trunks and branches showed surprising hardiness in Czech winters (USDA zone 6). They also proved to cope well with late winter temperature swings without any damage.
Holm oak is not too picky about soil type provided it is well drained. It can even take less fertile soil. Never plant it in heavy clay and water-logged sites where its roots may rot. Even moisture is needed in the first season after transplanting, then it will do with occasional rain. It loves sun and warmth, never plant it in exposed areas of zones 6 borderline. For cultivation in Central European conditions always look for plants with hardened wood which is not prone to frost damage. Pruning is best done in early spring and light trimming is possible in midsummer. Hardiness trialed and proved down to -24°C (USDA zone 6).
Last update 15-01-2023
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