Kwanzan Flowering Cherry Tree (Prunus ‘Kanzan’)

Japanese Flowering Cherry, Kwanzan Cherry

Kanzan is a cherry hybrid that has a Japanese name due to its long heritage, being bred in Japan in the Edo period between the 17th and 19th centuries. The flowers of the parent tree are white with occasional pink tinges, but this cultivar produces pure pink flowers in wonderful abundance, making it one of the world’s most popular ornamental trees.

I. Appearance and Characteristics 

Prunus ‘Kanzan’ (Prunus serrulata ‘Kanzan’. syn. Prunus lannesiana ‘Kanzan’, Cerasus Sato-zakura Group ‘Sekiyama’ Koidz, Kwanzan or Sekiyama, Japanese 関山) is a flowering cherry cultivar. It was developed in the Edo period in Japan as a result of multiple interspecific hybrids based on the Oshima cherry.

It is a deciduous tree that grows to between 1 and 9 metres (3 ft 3 in and 29 ft 6 in) high with an 8-metre (25 ft) spread. Young trees have a vase-shaped habit that becomes more spreading into maturity. In winter they produce red buds, opening to 5-centimetre (2 in) diameter deep-pink double flowers. The trees, which are usually propagated by chip budding or grafting, prefer a well-drained location in full sun.

‘Kanzan’ has pink petals, which are thought to have unexpectedly inherited the characteristics of the white Oshima cherry. The petals of the common Oshima cherry are white, but in rare cases, the petals are slightly pink due to the effect of anthocyanin, a biological pigment, and the petals are sometimes dark pink due to exposure to low temperature just before the flowers fall. The pink color of the Oshima cherry is generally suppressed in the wild, but it is thought that a mutation occurred during selection breeding to produce pink individuals, and then kanzan was produced.

‘Kanzan’ is the most popular Japanese cherry tree cultivar for cherry blossom viewing in Europe and North America. Compared with Yoshino cherry, a representative Japanese cultivar, it is popular because it grows well even in cold regions, is small and easy to plant in the garden, and has large flowers and deep pink petals. In the city of Bonn, Germany, there is a row of cherry trees where 300 ‘kanzan’ trees were planted in the late 1980s. In Western countries, ‘Pink Perfection’ and ‘Royal Burgundy’ originating from Kanzan have been created.

II. How to Grow and Care

Sunlight

Japanese cherry trees grow best in full sun, which means it needs at least six hours of direct, unfiltered sunlight each day to produce optimal blossoming. However, the tree can also tolerate partial shade.

Temperature and Humidity

Japanese cherry trees have been known to survive winter temperatures down to minus 10 degrees Fahrenheit, which means that they can be borderline hardy in the northern part of zone 5. Zones 5b to 8a are ideal climates, as more southern gardens may not provide the 45-degree winter dormancy these trees need.

Prolonged periods of cool, wet, and humid summer weather can be a problem for this species, since it fosters a number of fungi that can create serious disease for cherry trees

Watering

Japanese flowering cherry prefers plenty of moisture—at least 1 inch per week. Add a layer of mulch to the top of the soil to keep it moist and insulated, particularly during the winter months. Once well-established, Japanese flowering cherry will tolerate short droughts.

Soil

This type of cherry tree will tolerate a variety of soil types, but it prefers moist, fertile, well-drained loamy soil with a relatively neutral pH (6.7 to 7.1). Ideal soil will make this plant less susceptible to the many fungal diseases that can plague the species.

Fertilizing

Kanzan likes to be fertilized. A sufficient amount of fertilizer will ensure that it grows healthily and bears fruit. Organic fertilizer is usually used for its base fertilizer. When applying fertilizer, dig a circular trench around the external circumference of the tree crown, at a depth of 38 cm and a width of 28 cm. Apply the fertilizer evenly throughout the trench, then backfill the soil.

Fertilizer should be applied twice a year, the first time prior to blooming, to supply nutrients for the flowers, and the second time when the fruit is growing larger, to supply nutrients for fruit growth and to increase the yield.

Planting Instructions

You can purchase Kanzan saplings in garden centers. Pay attention to two things before planting. First, choose an area of the garden that has a lower altitude to plant your Kanzan. This will help it to acquire enough water because its roots are shallow. Additionally, apply sufficient base fertilizer before planting it, mostly organic fertilizer. Once planted, remember to water it soon after, until the water on the surface of the soil stops draining away. When this happens you have provided sufficient water.

We generally do not sow seeds to propagate Kanzan because the seeds need to undergo post-ripening effects. This means that the seeds are not yet mature when they are harvested. It is only after a period of special treatment that the seeds can complete their biochemical processes and reach the condition of being mature seeds that are able to germinate.

Pruning

Generally speaking, very little pruning is necessary for Prunus serrulata cultivars other than removing damaged branches. In fact, the more you prune, the more likely you are to allow fungal diseases to take hold.

If you need to prune, do so after the tree flowers. Always sterilize your cutting tools after each cut. Some limbs can grow too quickly and heavy for the base, so it’s best to prune away the heavy branches as needed.

Propagation

Most ornamental cherry trees are created by grafting branches from a selected cultivar onto the hardier rootstock of a wild cherry. Propagating them yourself is an uncertain prospect, as the plants resulting when you root stem cuttings will not have the hardy rootstock. The shape, size, and overall rigorousness can be quite different from your parent plant.

Cuttings should be taken from semi-hardwood branches during the summer months. If you wish to experiment with propagation by stem cuttings, here’s how to do it:

  • Choose a branch that has two to four leaf nodes and leaves.
  • Using sterilized pruning shears, cut off a 4- to 8-inch section at a horizontal angle and remove the leaves from the bottom two-thirds of the branch.
  • Dip the cutting into the rooting hormone.
  • Push the cut end into a mixture of half perlite and half sphagnum peat moss. Pat down the soil around it.
  • Place a loosely secured plastic bag over the container, then move the pot to a sunny location.
  • Mist the cutting twice a day to keep the soil moist.
  • After two to three months, gently tug on the cutting to see if it’s rooted. If there’s resistance, let the cutting grow until the roots have filled the pot.
  • When ready, transfer the plant to a gallon-sized container filled with potting soil. Move it outside to let it acclimate to the temperatures for a week before transplanting the tree to a location with full sun.

Potting and Repotting

Most ornamental cherry trees are too large for container growing, but it’s possible to grow Japanese flowering cherry trees in containers or even as bonsai plants if you choose a compact cultivar. Potted cultivars of P. serrulata require regular pruning. Such plants can make excellent patio specimens.

Use ordinary commercial potting soil in a large, deep, well-draining container (terra-cotta pots are best to aid in drainage). Repotting will be difficult, so start with the largest container possible.

Some experts recommend replacing a good portion of the potting soil every two to three years. Feed the plant with a good controlled-release fertilizer each spring. A potted tree will need to be watered regularly—several times a week in hot weather.

Overwintering

Over much of their hardiness range, Japanese flowering cherries require no winter protection. However, gardeners in the northern part of the range (zone 5) may want to mulch the ground around young trees with a thick layer of dry straw or leaves to protect the roots from cold over the winter months. Clean up fallen leaves and other debris to prevent fungal diseases and insect larvae from overwintering to reappear in the spring.

Pests and Diseases

Common Pests and Plant Diseases

Gardeners who want to enjoy the beauty of a Japanese flowering cherry should be prepared to spend considerable time treating pests and diseases in most years, but the spring bloom is worth it for many. In fact, their susceptibility to a number of pests makes most specimens short-lived. Careful care can keep the plant healthy enough to resist many problems, but don’t be surprised if your tree succumbs after 15 to 20 years.

Peachtree borers are a notable pest problem for cherry trees. For borer control, most experts simply advise keeping the tree vigorous (and therefore less susceptible to borer attack) by providing adequate irrigation and fertilizer. You can use spray pesticides formulated for peachtree borer to treat current infestations.

Other small pests that trouble this tree are scale insects, spider mites, and aphids. You can generally blast these pests off the leaves with a strong spray from your garden hose. Tent caterpillars will eat the leaves, so remove their silky nests as soon as you spot them and before much damage can be done. Japanese beetles can also feed on the tree’s foliage, and severe infestations can be controlled with spray insecticides.

A number of serious diseases can affect Japanese cherry, including leaf spots, dieback, leaf curl, powdery mildew, root rot, and fire blight. Consult your local Extension service for diagnosis and solution recommendations in your area.

Common Problems 

Japanese flowering cherry trees are prone to a number of growing issues. Keeping your tree healthy is the best preventive measure, but the Japanese flowering cherry is a tree that sometimes requires a professional arborist to diagnose and treat problems.

Bark Splitting

A significant problem is bark-splitting, whereby large cracks emerge in the trunk. Such a crack can allow organisms to enter and subsequently cause decay. As a solution, trace with a knife just outside the split in the trunk and then remove the bark from inside the traced area. This will prevent the crack from expanding. If the tree is otherwise healthy, the area should callus over to prevent disease.

Gummy Residue Around Trunk

This is often an indication that the tree is fighting peach tree borers. You may also see wounds and cankers on the trunk of the tree when borers are attacking. Permethrin or other powerful insecticides will likely be necessary to control these pests, but take care not to spray during the bloom period, as this will kill pollinating bees.

Ragged Holes in Leaves

This is usually caused when Japanese beetles are feeding on the foliage. One effective method of control is to use pyrethrin-based insecticides. Horticultural soaps can also be effective, though application on a full-sized tree can be problematic.

III. Uses and Benefits 

Japanese cherry trees can function in the landscape as fast-growing shade trees for small spaces like patios, or as specimen trees for spring display. Smaller cultivars can make good potted trees.

IV. Harvesting and Storage

The fruits of Kanzan usually ripen in the early fall and can be picked for eating. If the fruit needs to be stored or transported a long distance, it is better to harvest the fruit before it softens, such as during the late summer or early fall. Note that fruit should be handled gently and, ideally, and the twig should remain on the fruit.

Kwanzan Flowering Cherry Tree (Prunus ‘Kanzan’) Details

Common name Japanese Flowering Cherry, Kwanzan Cherry
Botanical name Prunus 'Kanzan'
Plant type Tree
Hardiness zone 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b
Growth rate Medium
Harvest time Summer
Height 25 ft. 0 in. - 36 ft. 0 in.
Width 25 ft. 0 in. - 36 ft. 0 in.
Sunlight Full sun (6 or more hours of direct sunlight a day)
Soil condition Clay
Flower color Pink
Leaf color Green