Ilex crenata, also commonly known as Ilex, Japanese holly, or box-leaved holly, is an evergreen shrub that is often used as a hedge or, in this case, a bonsai. It is native to eastern China, Japan, Taiwan, Korea, and Sakhalin (Russia).
In its wild habitat, it can be found on mountain slopes, in thickets, and in areas with forests.
This multi-branched shrub is very popular among bonsai enthusiasts due to its dense evergreen foliage. The leaves are dark green and quite small.
You can also expect your tree to produce small white flowers and if there’s a male and female tree around, small black berries will appear in the place of the flowers.
This tree can easily be confused with boxwood (Buxus).
Superficially they look very similar and are used in a similar fashion such as hedges and of course bonsai. These trees can be told apart by looking at the leaf arrangement. Ilex bonsai has alternate leaf arrangements where boxwood bonsai features opposite leaf arrangements.
This tree is sometimes sold as an indoor bonsai, but it does much better outdoors since it needs to be kept in a cool spot during winter and prefers a full sun location.
Japanese holly is quite frost-hardy when planted in the ground, but care should be taken to protect your tree if you’re keeping it as a bonsai in a pot.
There are multiple cultivars of Ilex available as bonsai. The cultivar Ilex crenata ‘Convexa’ for instance has domed leaves and grows in a very compact fashion. Other popular cultivars also include Ilex crenata ‘Stokes’ and Ilex crenata ‘Ivory Tower’.
If you’re an absolute beginner, then this tree is a great choice. It tolerates constant pruning and is quite forgiving.
Care Guidelines Japansese Holly Bonsai
Japanese holly is an outside bonsai and would be kept outdoors all year round. This little tree requires a lot of sunlight to stay healthy. Care must be taken, however, to protect it against the sun during the hottest part of the day in summer. Placing it in an area with full sun in the morning and afternoon but semi-shade during midday is perfect for this tree.
If your tree is planted in a bonsai pot, you will need to protect it against frost.
Your bonsai should be moved to a sheltered indoor location where the temperature never drops below 41° Fahrenheit (5°C).
Keep your tree away from heaters in a brightly lit room to create a dormant state to allow your tree some rest. You can also keep your tree on a window sill that gets full or partial sun when brought indoors.
If you don’t have a sunny window, you might need to supplement light with artificial grow lights to keep your tree healthy.
If possible, keep your tree on a sheltered porch or in a cold frame to protect it against cold winds and frost. Doing this is easier than bringing your tree indoors especially if you have a central heating system.
Japanese holly bonsai needs to be watered daily. This tree should never be allowed to dry out completely. It is best to do a moisture check every day to decide if your tree needs water. You can check the moisture by sticking your finger around 1 inch (2.5cm) into the soil.
If the surface soil feels dry or only slightly moist, water your tree thoroughly.
The only time you can skip watering your Ilex bonsai is if the soil feels soggy. In this case, allow it to dry out for another day before watering your plant again. This bonsai also requires more watering during the summer months.
Japanese holly also likes a humid environment.
For this reason, a humidity tray comes highly recommended especially if your tree will be kept indoors. Simply fill a shallow tray with flat stones and place your bonsai pot on top.
Fill the tray with water, but make sure the water doesn’t touch your bonsai pot.
This way the evaporating water will create a constant bubble of humidity around your little tree without making the roots soggy. You can also regularly mist your tree to provide some extra humidity as the water evaporates from the leaves.
Soil And Fertilizing
Ilex crenata bonsai are grown in pots with very little soil. This means that you have to fertilize your plant. It is especially important during the growing season if you want to keep your bonsai healthy.
To achieve this, simply use a liquid bonsai fertilizer at half strength every week during the growing season.
Once winter comes around, you can reduce fertilizing to once a month.
Another option is to use half the recommended strength of solid fertilizer once a month during the growing season. Once winter comes around, you can skip fertilizing completely during the three months of winter. Start fertilizing again once spring comes around.
It is important to adjust the strength of your fertilizer to prevent root damage. Bonsai grow in very little soil which means a build-up of salts from the fertilizer can do more harm than good.
Too strong fertilizer will also cause vigorous growth which is undesired in a bonsai.
Before you start pruning your Japanese holly bonsai, allow the new shoots to develop at least 4 new leaves. Once the new shoots developed the required number of leaves, you can prune away two of the four leaves.
You can keep your clippings to propagate them into new bonsai if you so desire.
Pruning should only be done in early to late spring if you want flowers and fruits to develop on your tree. You can also prune after your tree fruited to remove any dead flowers and fruits before winter starts.
Japanese holly bonsai require repotting every two years.
The best time to repot your tree is in spring just as the new buds are about to open.
Check your tree’s roots to see if it is ready for repotting. You can do this by gently lifting it out of the pot and checking if the roots are pot bound. If the roots are taking on the form of the pot, they’re pot bound and it is time to repot your tree.
If the roots still look ok and there is still lots of space to grow, you can return your tree to its pot and check again in a year’s time.
During repotting you can prune away about ¼ of the roots and either return your tree to its original pot or a slightly bigger pot to allow for healthy growth. The soil you use should be able to retain moisture quite well but still drain freely.
A good soil mix to use is a standard potting mix mixed with bark added for water retention or Akadama, pumice, and hummus mixed together to create soil for your little tree.
The recommended method to propagate Japanese holly is by taking cuttings. It is best to take semi-hardwood cuttings in late summer. You can also use the clippings you got during pruning in spring. Simply place these cuttings in a pot with their own soil and water and feed them the same as your bonsai. They will quickly develop roots and grow into a whole new little bonsai.
It is also possible to propagate Ilex crenata by using seeds. This method, however, requires a lot of patience. Seeds must be cold pre-treated and can take two to three years to germinate.
Potential Pests And Diseases
The Japanese holly bonsai is prone to attack by pests such as spider mites, vine weevils, and leaf-miner moths. Fortunately, these pests are easy to kill. All you have to do is use a store-bought pesticide for the specific pest you’re trying to get rid of.
You also have the option of making your own pest repellent at home without the use of harsh chemicals. Simply rub some neem oil on the leaves and affected branches or make a vinegar, dish soap, and water mixture to mist your plant with. Make sure to rinse the leaves and branches afterward and wipe away any visible pests.
You will have to repeat this process until all pests are taken care of.
Wiring Your Bonsai
The best time to do wiring on Japanese holly bonsai is in late spring and summer. Be very careful when you do attempt wiring since the branches of this tree are quite brittle and thus break easily while being bent. You will also need to protect the bark since it is quite prone to scaring caused by wiring. It is better to only train the new growth on this tree.
Older growth is set in its ways and becomes very brittle. Bending older branches should be done with extreme care.