The holm oak is the ideal tree for hobby gardeners who have a preference for the Mediterranean flair of the Mediterranean flora. It doesn’t bother her that Quercus ilex only endures the typical German winter in mild wine-growing regions. They cultivate the evergreen wood in large tubs without further ado, thereby emphasizing their individuality and expertise. Since the impressive holm oak is rarely found in gardens and parks, it has the aura of an exotic rarity, which is further enhanced by the sharply serrated leaves. In truth, the oak species certainly scores with pleasant undemanding, as the following care instructions state.
Table of Contents
- Oak (Quercus) plant genus.
- Scientific name Quercus ilex.
- Botanical spelling holm oak.
- Native to the Mediterranean coasts.
- Evergreen, partially hardy deciduous tree.
- Growth height between 5 m and 20 m.
- Cream colored kittens in April and May.
- First flowering after 30 to 40 years.
- Brown acorns in the cup from September.
- Smooth, brown-black bark roughens with age.
- Common names: green oak, holly oak.
The seeds can be eaten and taste sweet or bitter depending on how ripe they are. In pig fattening, the acorns of the holm oak as feed play a significant role in the world-famous quality of Iberian pigs and Iberian ham.
Since the southern holm oak has little chance of a successful hibernation outdoors in the local latitudes, knowledgeable hobby gardeners usually cultivate the tree in tubs. This has the advantage that the deciduous tree can be assigned an optimal position.
- Sunny to semi-shady location.
- Warm and airy at the same time.
Garden lovers who enjoy the privilege of living in a mild region of Germany prefer to plant their green oak in a sunny location. In this way, they minimize the risk that intense winter sun can damage the decorative bark.
substrate and soil composition
As a member of the oak genus, the holm oak is one of the slow-growing deciduous trees. As a result, the stable root system with deep taproots only develops over the years. At a young age, the roots are still quite sensitive, which prudent hobby gardeners take into account when choosing the substrate or the soil conditions in the bed.
- In the planter, the use of high-quality potting soil is recommended.
- The addition of lava granules, expanded clay or sand gives the substrate structural stability.
- In the bed, humus-rich, slightly loamy and gritty soil promotes growth.
Loosening the potting soil using coarse-grained materials makes sense because even when the soil is completely saturated with water, enough air is still transported to the sensitive roots.
watering and fertilizing
Irrespective of the genus they belong to, evergreen plants have a comparatively high need for water and nutrients. The holm oak is no exception in this respect.
- Keep the substrate constantly moist without causing waterlogging.
- Water daily during long dry periods in summer.
- Do not water overhead, but always directly to the roots.
- Apply liquid fertilizer every 2 weeks from April to September.
- Feed planted green oaks with compost in March and July.
Where no garden compost is available, experienced allotment gardeners use equivalent preparations from specialist shops and dose exactly according to the manufacturer’s instructions. In addition, a mulch layer made from grass clippings promotes the supply of nutrients and at the same time keeps the soil warm and moist.
A good pruning tolerance is the central premise for the cultivation of a Quercus ilex in the home ornamental garden and even more so in the bucket. In the wild, the majestic deciduous tree reaches heights of 20 meters and more, which is probably less desirable in the home garden. Fortunately, the holm oak meets this criterion, so that it is up to the hobby gardener to decide what growth height to achieve.
- The best time for pruning and topiary is late winter.
- Ideally in frost-free, dry weather without blazing sunshine.
- Cut branches that are too long just above an outward-facing eye.
- Cutting into the old wood must be avoided at all costs.
- Completely remove steeply ascending or inward branches.
- Thin out all dead wood and stunted growing shoots.
Sometimes it has a beneficial effect on the habit if the green oak is pruned in the lower area. The experienced gardener cuts off disturbing shoots in the lower trunk area up to just before the branch ring in order to emphasize the crown formation. This also includes eliminating disruptive water shots. A water shoot can be recognized as having sprouted near the root and has widely spaced buds. Such shoots are of no use to the holm oak. Rather, they only withdraw urgently needed nutrients and water.
Since the Quercus ilex can only endure a minimum temperature of -15° Celsius for a short time, it should always be hibernated in frost-free winter quarters in harsh areas. A bright, unheated conservatory is ideal. If possible, the temperature does not rise above +8° Celsius in order not to disturb the dormant vegetation of the tree. The darker the light conditions, the more leaves the holm oak sheds. However, this is no reason to panic. If all other conditions are right, a fresh, healthy shoot will appear on time next spring.
- Do not fertilize during the winter rest period.
- Water occasionally to keep the root ball from drying out.
- Water the bed regularly on frost-free days.
In addition to the dreaded frost (negative temperatures without snow), direct exposure to the winter sun represents a considerable risk factor for the green oak. In this case, the bark threatens to tear and burst because it cannot withstand the temperature fluctuations. This not only ruins the visual appearance, but also gives viruses, fungal spores and pests unhindered access. While commercial trees are protected from such damage by painting them white, this measure on an oak tree is perceived as a disfigurement. The problem is solved using special shading nets or air-permeable garden fleece.
If the cultivation of a first holm oak is crowned with success, its proud owner also has plenty of material for the most uncomplicated propagation using sticks.
- Towards the end of winter, cut off healthy, strong sticks.
- A suitable stick has at least 3 to 4 sleeping eyes.
- Cut the tips of the branches straight and cut the lower ends at an angle.
- Fill several growing pots with a moist, low-nutrient peat-sand mixture.
- Plant 2/3 of the sticks one at a time, with the sloping cutting point pointing downwards.
Placed in a light, frost-free spot, new roots will sprout from the leaf nodes. The substrate must not dry out during this phase. In the spring, new leaves begin to sprout as evidence that a young root system is developing underground. The rooted cuttings are planted out in the garden or in the bucket.
- Pick some healthy acorns from the tree in early fall.
- Carefully separate the fruit cup from the nut fruit.
- Fill a bag with damp sand and the acorns.
- Store in the vegetable drawer of the refrigerator for 6 to 8 weeks.
- Then plant each acorn in a 5 cm pot in potting soil and peat mix.
- Insert with the small root down, just below the surface.
Placed on the warm, bright south-facing window, the seedling must not dry out under any circumstances. As soon as the thumb test shows that the top layer of the substrate is beginning to dry, the next dose of water is administered. In the weeks and months that follow, each seedling tries diligently to root through the pot. From a height of 10 cm to 15 cm, growth is so advanced that the young tree is repotted in a larger planter. This process is repeated until the holm oak has reached a satisfactory size to be cultivated as an adult specimen.
The leisurely growing Quercus ilex is repotted on average every 2 years. The best time for this care measure is spring, before the new shoots begin.
- The new bucket is only a few centimeters larger.
- There is an opening at the bottom for water drainage.
- Above that, the hobby gardener lays a drainage made of gravel or perlite.
- The potted green oak is planted together with the fresh substrate.
Experienced hobby gardeners use the transplant as an opportunity to take a close look at the root ball. If necessary, they remove diseased root pieces and trim the taproot. They seal the cuts with charcoal ash, which also has a disinfecting effect.
Care as bonsai
The holm oak enjoys high esteem as an outdoor bonsai during the months of March/April to November. Last but not least, it is the high life expectancy of 200 to 500 years that encourages hobby gardeners all over the world to celebrate the art of the small trees on the Quercus ilex in order to pass it on to the next generation. With regard to care, there are a few differences to the ‘big brother’ in beds and tubs that need to be taken into account.
Due to the limited space available in the bonsai pot, the green oak needs as much light as it can get hold of. Since the taproot is practically non-existent in such a culture, only photosynthesis provides the excess energy required for growth. Consequently, in this case, the only option is a full sun position.
holly oak as a bonsai is regularly showered with collected rainwater. At this point, the lower root volume is noticeable again.
The central art of bonsai culture is revealed in the regular ritual of pruning and pruning, based on Asian traditions that are thousands of years old.
- Cut back branches and shoots every 6 to 8 weeks from May.
- When repotting, also prune roots.
The primary goal of every cut is to generate and maintain a harmonious size relationship between trunk, roots and crown.
What cannot be achieved in bonsai design with a cut, the skill of wiring can do. The bonsai gardener uses aluminum wire to give the trunk and branches the desired shape. All wires are removed by mid-May at the latest, because the holm oak then enters the phase of thickening.
In all other care aspects there is no significant difference to the large holm oaks in beds and tubs.
The holm oak sets distinctive accents in the tub on the balcony and terrace without requiring extensive care. As long as its desire for sufficient water and nutrients is met, the Quercus ilex adorns the garden with decoratively toothed, evergreen foliage from April to November.