How to Grow and Care for Japanese Black Pine

Japanese black pine is an attractive irregular needled evergreen that usually does not grow with a straight central leader but instead matures into a flat-topped specimen with drooping branches. If there is a predominant leader, it is often a thick twisting structure rather than a straight trunk. The tree has long dark-green needles with contrasting silky white candles with an upright new growth. Japanese black pine grows best in sandy loam and in a sunny location. It is a good choice for salty locations, such as seashores, and it does well in both acidic and alkaline soils. It is also one of the most popular of all pine species for bonsai.

Japanese Black Pine Care

Here are the main care requirements for growing a Japanese black pine.

• Give the tree six hours of direct sunlight a day.
• Plant in well-draining soil; this tree dislikes soggy soil.
• Space trees at least 12 feet apart if growing them as screening, as these dense trees will quickly fill in.
• Prune in the spring during dry periods to avoid fungal issues.

Light

Japanese black pine should get at least six hours of direct sunlight daily. Some light afternoon shade is acceptable.

Soil

The soil must be moist but well-drained. Sandy loam is ideal; Japanese black pine does not tolerate soggy soil and poor drainage. It prefers acidic soil but can also grow in slightly alkaline soil.

Water

After you plant the tree, make sure it gets a full 1 inch of water per week for the first year. After the tree is established, it will be quite tolerant of short droughts and may not require any irrigation beyond ambient rainfall.

Temperature and Humidity

This tree generally does well in USDA zones 5 to 8. Winter burn will seriously damage the tree at temperatures below minus 10 degrees Fahrenheit, turning needles dry and brown. Humid conditions may foster fungal diseases, especially if pruning is done during wet periods.

Fertilizer

This tree, like most pines, does not usually require regular feeding. If your soil is poor in nutrients, add a complete fertilizer in the spring. Potted bonsai specimens, however, can benefit from more frequent feeding.

Types of Japanese Black Pine

The pure species form of Japanese black pine is very popular in landscape use. In ideal locations, the pure species can grow to be quite a large tree, up to 80 feet tall. Many popular cultivars are dwarf varieties, some of which remain only 3 to 10 feet tall. Some favorites include:

• 'Majestic Beauty': This is a fast-growing cultivar with beautiful deep-green needles and it often reaches 40 to 50 feet in height within 20 years.
• ‘Oculus Draconis’: This variegated dwarf variety has needles with a yellow band close to the base and grows to a mature height of 6 to 8 feet.
• ‘Shirone Jamone’: The variegated cultivar has bright golden or yellow bands on dark green needles. It grows up to 10 feet high and 7 feet wide in a decade.
• 'Thunderhead': The dwarf cultivar grows 5 to 10 feet tall in a decade. Its branches are densely needled, giving the appearance of dark storm clouds.
  
• ‘Pygmaea’: This compact cultivar has full-length needles and grows only about 5 feet in 10 years.

Pruning

Although pruning is not necessary for the tree's health, its irregular growth pattern and drooping branches may require regular pruning to make room for people and vehicles to pass underneath the canopy. Pruning can also help the trees remain dense and full when they are planted as a screen. Often, pruning is done to deliberately shape the tree into twisted, exotic shapes, exaggerating its natural growth habit. Its ability to handle this kind of pruning makes it a popular tree for bonsai practice.

Major pruning of landscape trees is best done in the spring, preferably during dry weather when transmission of fungal diseases is less likely.

When Japanese black pines are grown as bonsai plants, pruning usually involves pinching off the new growth candles in the spring, as well as regular root pruning to keep the tree small.

How to Grow Japanese Black Pine From Seed

As a group, pines are somewhat difficult to propagate by vegetative methods, such as by rooting branch cuttings. For this reason, propagation is more commonly done by seeds extracted from the cones or purchased from a commercial source. Harvested seeds from ripened cones are fairly easy to germinate and grow into seedlings. Here's how to do it:

1. Collect cones in the fall as they begin to fall from the tree, then store them to dry through the first part of winter.
2. Harvest the seeds from the cones in late winter when you are ready to start them indoors. Extract the seeds by drying mature cones until the scales begin to separate, then shake them over a sheet of paper to dislodge the seeds.
3. After shaking the seeds loose, soak them in water for 24 hours, put the seeds in a plastic bag, and place them in the freezer for four weeks.
4. Fill small pots with standard potting mix. Sow the seeds on the surface and cover them with 1/8 inch of vermiculite or fine compost.
5. Gently water the pots and place them in a bright location at room temperature. Within 14 days, the seedlings should germinate and sprout.
6. Grow the developing seedlings outdoors in full sun, keeping them uniformly moist. Repot them into larger containers as needed. In the first year, they should reach a height of several inches.
7. In about two years, the seedlings will be of sufficient size to plant in their permanent locations in the landscape.

Potting and Repotting Japanese Black Pine

Container culture for Japanese black pine usually is done only when the tree is being grown as a bonsai specimen. Bonsai trees are normally grown in a typical bonsai potting mix of coarse sand, clay, or pumice, and peat in a traditional ceramic bonsai pot.

As with most bonsai plants, Japanese black pines should be repotted every few years to prune back the roots. Japanese black pine, like most bonsai, likes to have its roots rearranged before repotting back in the same container with fresh potting mix.

If you keep it outdoors—or bring it outdoors for the summer—the container must be protected from the hot sun to prevent root burn. In partial shade, the needles will be lighter than a tree grown in full sun. Water it regularly but let the soil dry out to the touch between watering.

Pruning stresses the bonsai tree and causes sap bleeding. Do substantial pruning only between fall and early winter. If you need to do minor pruning during the summer, make sure to move the container into the shade for about a month afterward to minimize sap bleeding.

Overwintering

Like most pines, Japanese black pine can be susceptible to winter burn if grown in regions where it is borderline hardy. Zone 5 gardeners may find that their Japanese black pine develops browned needles on the side that faces cold winter winds. This is most likely to occur with young trees, or in situations where temperatures fall quickly from warm fall weather into freezing winter cold.

Young trees can be protected from winter burn by planting them in sheltered locations and making sure they are well-watered going into winter. Mulching the soil well is also beneficial. If necessary, small trees can be protected with a tent or screen of burlap for the winter. Do not, however, tightly wrap the trees with burlap, as this can trap moisture and foster fungal infection.

Common Pests & Plant Diseases

A variety of pests can affect Japanese black pine, but the most serious is the pinewood nematode, which often kills the tree. These tiny soil worms infect trees through holes bored by bark beetles. Very quickly after infection, the tree will begin to fade color and turn yellow, and the tree often dies within a year or two. There is no cure for this disease, so it is important to diagnose it quickly and remove affected trees to prevent its spread to other pines.

Other possible pests include sawflies, Nantucket tip moths, and bark beetles.

Japanese black pine is a fairly problem-free plant when it is young, but as the tree approaches about 20 years of age and begins to set cones, Diplodia leaf blight (a fungal disease) often sets in. Beginning with the lower branches, needles begin to defoliate, giving the tree a shabby appearance. Gradually, cankers may form on branches. Leaf blight that progresses into canker disease is usually fatal.

Other fungal diseases are also possible, including various rusts and cankers. All these fungal diseases can be slowed by good hygiene (sweeping up needles and removing affected branches) and spraying with fungicides each year when new growth is starting. Badly affected trees that have developed cankers from Diplodia can't be cured. Avoid pruning during wet weather when fungi are easily transmitted. In addition, avoid fertilizing lawns around pine trees, as excessive nitrogen also fosters fungal diseases.

Common Problems With Japanese Black Pine

Other than the all-too-frequent decline of Japanese black pine when the trees become mature and susceptible to common diseases, this is a largely problem-free tree for the first 10 to 20 years of its life. Because it is a very attractive tree, many gardeners are often delighted to use it in the landscape with the understanding that it will need to be removed someday.

Low-Hanging Branches

It's a common complaint that the tree has low-hanging branches, making it difficult to walk beneath. This issue can easily be rectified by pruning.

Excessive Shedding

This tree is surprisingly messy because it sheds a considerable volume of needles and cones. This is not unusual for a pine tree but P. thunbergii's very dense growth is messier than most pines.

Brown Needles

Cold winter winds can dry out needles and turn them brown.