BONSAI ROVERELLA

The Oak Bonsai: The Oak of Our Hills

The Downy Oak(Quercus pubescens) is the essence that embodies the Italian hilly landscape. It is a "character" oak, robust and austere, prized in bonsai for its bark that turns gray and flaky with age and for the charm of its lobed leaves. A distinguishing feature of it is its "tomentosity" (a fine down underneath the leaves) and the phenomenon of rot: the leaves dry out in autumn becoming bronze in color but remain attached to the branches throughout the winter, falling only when new buds emerge in spring. It is a bonsai tree that teaches the rhythm of the seasons.

Origin & species

Native to southern Europe and Asia Minor, it is the most common oak tree in Italy. The Latin name pubescens refers precisely to the down that covers the young leaves and twigs. It is an extremely adaptable plant, able to live on dry, calcareous soils where other oaks would suffer.

Exposure and Microclimate

Downy oak loves full sun.
Direct light is essential to reduce leaf size and maintain short internodes. In addition, sun and air are the best antidotes against powdery mildew (White Mal), to which this species is particularly susceptible because of the down on its leaves.
It withstands heat and wind well. Do not keep it in shady or poorly ventilated places.

Watering

This is a plant that tolerates short periods of drought well, but in a bonsai pot it needs regularity.
Water when the soil feels dry to the touch. Avoid soaking the soil constantly: oak roots fear rot and asphyxiation. In winter, water sparingly, just so the root ball does not dry out completely.

Water quality

This is a very hardy plant that grows naturally on calcareous soils.
It tolerates tap water without any problems. It is not necessary to use osmotized water or acidify, unless the water is excessively hard or saline.

Substrate

Prefers draining and neutral or slightly basic (calcareous) substrates.

  • Recommended mix: 60% Pumice (good for oaks), 30% Akadama and 10% Universal Potting Soil.
  • Pumice provides needed aeration for the roots and simulates the rocky soils where it often grows in the wild.

Repotting

It is done in late spring (April-May), when the buds swell conspicuously.
It is repotted every 3-4 years. As with all oaks and beeches, the roots live in symbiosis with a fungus (mycorrhiza). Never wash the roots bare and always leave some old soil around the trunk so as not to lose this vital bacterial flora.

Fertilization

Fertilize with solid organic fertilizer in spring and fall.
In spring it is needed to support new growth, but do not overdo the nitrogen to avoid giant leaves. Fall fertilization is essential to harden the wood and prepare the buds for the following year.

Flowering and fruiting

It produces acorns, but it is rare to see them on bonsai grown in small pots, as they require a lot of energy and the plant must be mature. If they do form, it is advisable to remove them so as not to weaken the tree.

Structure pruning

Large setting cuts are made in winter.
The wood of the Downy Oak is hard and durable. It is mandatory to protect cuts with mastic, because oaks tend to withdraw sap creating dryness if the wound remains exposed. Dry or broken branches can be worked into "Jin" to give a vined look.

Maintenance pruning

During the growing season, the Downy Oak produces vigorous apical shoots. Shorten them regularly to redistribute strength to the low, inner branches, which are otherwise likely to decay.

Stapling

To thicken the canopy, shear new shoots when they have produced 4-5 leaves, shortening them to 2.
Defoliation (total or partial) in June is a very effective technique on Downy Oak to shrink leaves, but should only be done on trees that are in perfect health and well fertilized.

Tying & bending

Oak branches become stiff very early and are difficult to bend once lignified.
Wire tying is done on young twigs in spring/summer. For large branches, guy wires are the best and safest way to change the angle without breaking the wood.

Diseases and pests

  • Powdery mildew (White Mal): The real Achilles heel of the Downy Oak. The down on the leaves traps moisture favoring this fungus (white powder). Prevent with sun exposure and sulfur treatments in spring.
  • Aphids: On tender shoots.
  • Mealybug: Under leaves or in bark crevices.

Winter & protections

This is a very cold-hardy tree.
It can be outdoors all year round. Only during very intense and prolonged frosts (below -5°C/-10°C), protect the pot with mulch to safeguard the capillary roots. Dried leaves remaining on the branches (rotting) offer natural protection to the buds from the freezing wind.

Annual calendar

  • January-February: Structural pruning, cleaning.
  • March-April: Revival, preventive treatments Powdery mildew (Sulfur).
  • May: Repotting (late spring), fertilization.
  • June: Defoliation (if needed), stapling.
  • July-August: Regular watering, control White Sickle Cell.
  • September-October: Fall fertilization (PK).
  • November-December: Leaves turn brown but remain on the tree.

Useful products for this bonsai

Frequently Asked Questions about the Downy Oak

Why don't dry leaves fall in winter?
It is a phenomenon called rot, which is typical of many young oaks and beeches. The tree does not form the separation layer in the petiole in the fall, keeping the dry leaves attached to protect the buds from frost. They will only fall in the spring pushed by the new leaves.

What is that white powder on the leaves?
It is powdery mildew (or White Mal). Downy Oak suffers a lot from it in spring and fall if there is moisture. It should be treated immediately with specific products or wettable sulfur, and the plant should be moved to full sun and wind.

Can I harvest it in the wild (Yamadori)?
Oaks have a very deep taproot (central root) and few fine roots near the trunk. Harvesting in the wild has a very high failure rate if you are not experienced. Better to buy pot-grown plants or start from acorn.