Dwarf Cryptomeria Bonsai Care Guide
Cryptomeria japonica or Japanese cedar is an evergreen conifer endemic to the moisture-rich Japanese mountains. The tree may grow to over 100 feet in its natural environment and is favored in its homeland as both bonsai and ornamental.
Despite its name, this species is not a true cedar.
While japonica is the only species in its genus, there are many cultivars that are appropriate as bonsai art. Some favored varieties include Cryptomeria japonica 'Tansu' and Cryptomeria japonica 'Lobbi Nana'.
The fibrous, reddish bark and tiny green needle-like leaves make for a striking bonsai. It is naturally conical, and the dense, blue-green foliage turns reddish-brown in the winter, then green again come spring. Even though it is not a true cedar, it does share the slow-growing characteristic typical of cedars.
The Japanese cedar prefers full sun, at the most light shade, and is fairly hardy but must be protected from heavy winds and extended freezes. The needles are sensitive to too much hot sun or too vigorous of winds, and may turn brown under exposure.
If you bring the tree indoors in the winter, humidity levels must be adequate because drying out can kill this species. This can be achieved through the use of a humidifier, humidity trays, or tents. Placing the specimen in the bathroom can be helpful as well, as it will soak up all the steam produced by baths and showers.
Watering should be moderate – the Cryptomeria is native to rather damp locations and so can tolerate "wet feet". It should be planted in well-draining soil, and usually needs watering every day, enough to keep the soil from becoming completely dry.
Feed your tree a diluted, well-balanced mixture every two weeks throughout the growing season. In fall, switch to a nitrogen-free fertilizer such as 0-10-10.
The straight trunk and traditional conifer shape of this species lends itself well to being styled as a formal upright. It is also suitable for a forest or landscape grouping. The dense foliage of this bonsai requires that new growth be aggressively pruned to keep tangling and overlapping branches and shoots under control. This also allows for air and light to nurture the remaining foliage and makes for an environment that is less friendly to pests and disease. New growth should be pinched, not clipped, to avoid browned tips.
Remove undesirable upper branches as soon as possible to avoid losing trunk taper. The bark of the Japanese cedar is amenable to jins formed from the pruning of unwanted branches. Prune (and wire, if desired) this tree from spring all the way through summer, allowing the plant to rest in winter. It is fragile after being worked on and extra care should be taken to mist it multiple times daily as well as protect it from wind and sun for a few weeks afterward.
The seeds of Cryptomeria can be planted outside in the spring. The tree can also be propagated by layering, or by softwood cuttings taken in the summer and early fall. Take 3" cuttings and pot them with rooting hormone in a moist soil mixture. Place in a shady spot in order to encourage a healthy root system to develop.
This is best done in the late spring, and using a pot that isn't too shallow as this bonsai likes a good deep root run. Frequency will depend upon age and growth rate, ranging from every two to every five years. The older the tree, the less often it will need to be repotted.
A slightly acidic soil mixture of organic matter should be used (an equal ratio of peat and grit works well) and there needs to be adequate drainage. Do not root prune too aggressively, and it's wise to give the plant a full year after selective foliage pruning to prune the roots at all.
Insects/Pests & Diseases:
Like most densely needled trees, this bonsai can be vulnerable to red spider mites. These can be controlled with a spray of a teaspoon of dish soap in one quart of warm water. Rinse the foliage well with tepid water. Scale can be removed manually – by picking each one off by hand – or by applying rubbing alcohol to each insect and then gently removing them with a knife, being careful not to damage the bark. Once the adults are removed the entire tree must be inspected for eggs.
This bonsai can also be affected by leaf spot and leaf blight. Blight can cause browning of interior foliage, which makes for an unattractive specimen. Trimming and pruning to allow for air circulation will help keep the foliage dry, which can help prevent these problems. Fungicide may be used if needed.