Japanese holly is toxic to humans, dogs, and cats. It is considered invasive in some areas. Once mature, the shrub typically needs watering only during dry spells and feeding once a year but can benefit from the addition of compost and mulch. The plant doesn’t need a lot of pruning unless you’re aiming to train it in a particular shape, such as a curving topiary.
Light
Japanese holly grows best in full sun to partial shade. In warmer climates, it will appreciate some shade from the harsh afternoon sun. But in cooler climates, it typically should have full sun or at least six hours of direct sunlight on most days to grow its best. Too little light will result in slower growth and less dense branching.
Soil
This shrub can tolerate a variety of soil types, from sandy and rocky soil to clay soil. Ideally, it should be planted in loose, loamy soil that has good drainage. It prefers a slightly acidic soil pH.
Water
Japanese holly plants like a moderate amount of soil moisture. Keep young shrubs in evenly moist but not soggy soil to help them establish their root systems. Mature shrubs have some drought tolerance, and they also can tolerate occasional flooding. However, sitting for too long in wet soil can cause the foliage to turn a pale green and ultimately rot the roots, killing the plant. Water whenever you can stick your finger into the soil and it feels dry a couple of inches down. To help maintain adequate soil moisture and keep the roots cool, add a two to four-inch layer of mulch around the shrub.
Temperature and Humidity
Japanese holly prefers a temperate climate and doesn’t do well in extreme temperatures, both hot and cold. It is best to plant your shrub in a spot that is protected from harsh winds, which can damage the foliage during the winter. The shrub also tends to struggle in areas with high humidity and instead prefers average humidity levels.
Fertilizer
Apply a slow-release fertilizer in the spring as new growth begins. It also can be beneficial for healthy growth to mix some compost into the soil around the Japanese holly shrub.
Types of Japanese Holly
There are several varieties of Japanese holly, including:
Ilex crenata ‘Dwarf Pagoda’ is a small cultivar that only reaches around two feet in height with a very compact, dense growth habit.Ilex crenata ‘Golden Gem’ is a variegated cultivar.Ilex crenata ‘Convexa’ reaches around five to six feet in height and is known to heavily bear black fruit.Ilex crenata ‘Helleri’ is a dwarf variety that slowly grows to around two to four feet tall and three to five feet wide.Ilex crenata ‘Lemon Gem’: This is a small cultivar that doesn’t often grow taller than three feet and features yellowish foliage in the spring that matures to lime green.Ilex crenata ‘Sky Pencil’: With its narrow, columnar shape and height of six to eight feet, this cultivar is a preferred choice for a living fence.
Pruning
Japanese holly shrubs don’t need much pruning. But they can be cut back as needed to maintain the desired shape. They generally can handle light pruning at any point in the spring to early fall, though any substantial pruning should be performed in the early spring before new growth starts. Avoid pruning roughly two months before the projected first frost in the fall, as pruning can encourage tender new growth that the frost will damage. Remove any dead, damaged, or diseased branches as you spot them. To shape your Japanese holly into a hedge or topiary, lightly prune it several times during the growing season. Don’t severely prune it into your desired shape all at once. However, if you have an old shrub that needs rejuvenating, cut it back in the late winter to roughly six to 12 inches off the ground. This will encourage healthy new branches to grow and reform the shrub.
Propagating Japanese Holly
During the dormant season, Japanese holly can be propagated from hardwood cuttings:
Growing Japanese Holly from Seed
Most Japanese hollies grown in the landscape are cultivars whose seeds won’t produce a plant that is true to its parent. Also, even in ideal conditions, germinating the seeds can take years and it is erratic. Therefore it is not recommended to grow Japanese holly from seed.
Potting and Repotting
Dwarf varieties of Japanese holly are suitable for container growing. Choose a container that is at least eight inches wider than the root ball of the plant to give the shrub room to grow for the next two to three years before upgrading to a bigger container. Terracotta is ideal because it lets excess moisture evaporate and it is heavy enough so the container does not topple over easily. Fill it with a well-draining potting mix and make sure the container has large drainage holes.
Overwintering
Japanese hollies are hardy to USDA zone 5 and, generally, need no winter protection when planted in a suitable location sheltered from strong winds. But they benefit from several inches of mulch over the roots to protect them from the freeze-thaw cycle. The mulch should be spread as wide as the reach of the branches. The roots of Japanese hollies in containers are susceptible to root damage from winter cold and should be winterized with an insulating silo.
Common Pests & Plant Diseases
Japanese holly can be affected by the holly leaf miner whose females suck fluids out of the leaves in the late spring. Other pests include scale, whiteflies, and spider mites. As for plant diseases, root rot, stem cankers, and nematodes are the most common ones that can be damaging to the plant.
How to Get Japanese Holly to Bloom
Japanese holly takes two to three years of growth to bloom for the first time. If yours isn’t blooming and you have grown it from a cutting, it might be too young.
Common Problems with Japanese Holly
A common issue is yellowing leaves. This is usually a sign that the soil is too alkaline, which causes iron deficiency in the plant, although there might be sufficient iron in the soil. Hollies can only absorb iron when the soil is slightly acidic, To remedy this, feed it an acid-loving tree-and-shrub fertilizer and follow the label instructions.
