Pinus halepensis, also known as the Aleppo pine or Jerusalem pine, is a very interesting species to use for bonsai. In contrast to the more commonly used pines such as Japanese Black Pine, pinus halepensis can display two foliage types - juvenile or mature. This gives us options stylistically as well as an interesting horticultural challenge when controlling foliage in an Aleppo pine bonsai.
Here's what we'll cover:
- Aleppo pine bonsai
- Pests and disease
- Position in the garden
Aleppo pine bonsai
Pinus halepensis is an evergreen conifer native to the western Mediterranean, mainly the coastal regions. As it thrives in hot areas Aleppo pine is a very drought-resistant species. It can be found in mountainous areas, but generally grows better at lower altitudes.
In the ground, Aleppo pine is a medium-sized tree, which can help with scale when miniaturizing for bonsai. Needles can grow to 5cm-10cm and reduce in length very nicely when trees are containerized.
Although they are found in hot climates, pinus halepensis is a relatively frost-tolerant species. The Royal Horticultural Society has categorized Aleppo pine as an h5 hardy tree, meaning it can handle winter temperatures of -10°C to -15°C. This tolerance will be less once in a bonsai container, but they can survive very well without protection in moderate winter conditions.
Pinus halepensis is an interesting pine species for bonsai because it has two types of foliage - juvenile and mature.
Juvenile foliage is soft and fleshy. It is much shorter than mature foliage and has a more flat, leaf-like appearance. It is similar in some ways to Larch foliage.
Mature foliage is harder, has a waxy covering, and is much longer than juvenile foliage. It is the same as you would see on other pine species.
When pruning an Aleppo pine bonsai it's important to define your goals before you do any cutting, because the tree will respond with different foliage types based on how you prune it.
Many practitioners prefer the traditional look of the mature foliage, while others explore pinus halepensis material for the potential of creating a tree using juvenile foliage.
The great benefit of juvenile foliage in building a bonsai is if you fertilize heavily and cut back your bonsai a couple of times per year, you can quickly develop a ramified bonsai with tight internodes.
However, the tradeoff with this is you will usually have a mix of mature and juvenile foliage, which can look quite cluttered.
If you want to have mature rather than juvenile foliage, it's best to leave longer between prunings. An annual pruning paired with pinching in spring can help to maintain the silhouette of your tree without stressing it so much it pushes juvenile growth.
Wiring can be performed through most of the growing season, although it is best done during early spring (before growth starts) or early autumn after the heat of summer has passed.
Wire should be applied at a roughly 60° angle and wrapped in the same direction you wish to bend the branch.
If you are looking to create a traditionally styled bonsai, then branches should angle downwards from their origin.
However, if you want your Aleppo pine to be more reflective of the natural species then you may want to experiment with angling them upwards and outwards. This is how the species grows on the coast, often with strong directionality from Mediterranean winds.
Wire should be left on the tree until you start to see it bite it. Wire biting means that there is likely enough growth to hold the bend in place, and the rough bark that pinus halepensis produces will quickly grow out any scars.
Like most other pines, Aleppo pines like to be kept on the drier side. By reducing the frequency of your watering you allow good oxygen permeation into the rootball which stimulates root growth.
When you do apply water you should thoroughly drench the rootball to be sure all parts are saturated with water.
If you're interested in the finer points of bonsai watering, take a look at our bonsai watering checklist.
Pine bonsai rely on their roots as their source of health and Aleppo pine is no different. There are some important things to remember when repotting pinus halepensis.
Your bonsai should only be repotted in late winter or early spring, around the time that new growth starts to emerge. Repotting at other times of the year can be risky.
You should aim to repot as little as possible. Many bonsai can stay in the same container for 6-8 years, depending on their age and growth rate. Younger trees will produce more roots and require repotting more frequently.
The benefit of repotting less often is it allows the small container to fulfill its role in constricting the root mass, which scales back top growth and creates a more refined tree.
Indicators for repotting include the soil becoming too congested for water to pass through the rootball or soil starting to decompose and holding too much water. This latter one is important because if it isn't addressed the wet conditions can read to root death and in the worst extreme root rot.
When repotting, it's important to always maintain a portion of the root ball untouched. With deciduous trees, it's possible to wash the roots to remove old soil, but with pines, your bonsai will do better if you keep a portion of the old soil intact, even if it isn't great quality soil.
The reason for this is pines rely on the relationship between roots and microorganisms in the soil (known as mycorrhiza) for their function and health. The microorganisms help the roots to take up water and keep the tree hydrated.
If you remove all the soil on the root ball, you lose that precious relationship. By keeping a portion intact it provides a starting point for the re-establishment of the relationship in the rest of the pot.
Fertilizer is not an essential element for your bonsai tree's survival, but it is important in maintaining health. Trees generate their energy stores entirely through photosynthesis, so remember that fertilizer isn't a 'feed' as many sources will state.
Fertilizer is a growth stimulant and can provide a source of important micronutrients to keep your tree healthy.
In bonsai, fertilization is tailored to the species of tree you are working with and the stage of growth and development it is at.
Trees in early development will benefit from strong fertilization throughout the growing season. This promotes strong root growth, dense foliage growth and will help with the thickening of the trunk and branches.
After you have established the primary lines of your tree and it is settled in a bonsai container you should fertilize moderately to encourage back budding and secondary branch development.
Finally, once your pad structure has been developed you should fertilize only lightly. This provides micronutrients and stimulates some growth, but shouldn't make the tree blow out its refined foliage.
If you're in doubt about whether to fertilize a refined bonsai, it's usually better to air on the side of caution and not fertilize - remember it is not an essential element for bonsai growth.
With pinus halepensis specifically, the more you fertilize the more likely it will be the tree grows juvenile foliage. You can use this as a tool.
Pests and disease
Pinus halepensis bonsai are more susceptible to pests than other pines due to their softer and fleshier juvenile growth. They can be affected by aphids, adelgids, spider mites and pine shoot moth. These can usually be treated with one or more of:
- Water eradication
- Horticultural soap
Aleppo pine can be affected by pine needle cast, which can present as yellowing or browning of needles before they are shed by the tree. It can be treated with a fungicide to prevent further spread.
Position in the garden
Pinus halepensis enjoy growing in full sun and thrive in warm climates. If a tree is newly repotted or suffering from an infection or disease you may wish to place it in morning sun and afternoon shade.
As mentioned above, Aleppo pines are fairly frost-hardy and can generally be overwintered outside. You may wish to heal them in with mulch or place them in a cold frame if there are concerns about a tree's hardiness.
Can you grow pinus halepensis bonsai indoors?
Aleppo pine bonsai are commonly advised as indoor bonsai, but I would not recommend growing them inside. Although they come from a hot climate, they still experience a change in seasons over winter which is a necessary part of their growth cycle.
This cannot be replicated indoors, and you will struggle to grow a tree inside over the long term.
Pinus halepensis can be propagated via seed. They grow green cones that turn brown over time and can remain on the tree for years. These cones contain seeds that can be used to propagate more trees.
Like most pines, pinus halepensis is a challenge to propagate as cuttings.