Abies koreana, Korean Fir is a species of fir native to the higher mountains of South Korea, including Jeju Island. It grows at altitudes of 1,000 to 1,900 metres in temperate rainforests with high rainfall and cool, humid summers, and heavy winter snowfall. The Korean fir is a very popular ornamental plant in parks and gardens in temperate climates, grown for its foliage but also the abundant cone production even on young trees only 1 to 2 metres tall.
I. Appearance and Characteristics
Abies koreana (Korean: 구상나무, Gusang namu), the Korean fir, is a species of fir native to the higher mountains of South Korea, including Jeju Island. It grows at altitudes of 1,000–1,900 metres (3,300–6,200 ft) in temperate rainforest with high rainfall and cool, humid summers, and heavy winter snowfall.
It is a small to medium-sized evergreen coniferous tree growing to 10–18 m (33–59 ft) tall with a trunk diameter of up to 0.7 m (2 ft 4 in), smaller and sometimes shrubby at the tree line. The bark is smooth with resin blisters and gray-brown in color. The leaves are needle-like, flattened, 1–2 centimeters (0.4–0.8 in) long and 2–2.5 millimeters (0.08–0.10 in) wide by 0.5 mm (0.02 in) thick, glossy dark green above, and with two broad, vividly white bands of stomata below, and slightly notched at the tip. The leaf arrangement is spiral on the shoot, but with each leaf variably twisted at the base so they lie mostly either side of and above the shoot, with fewer below the shoot.
The shoots are green-gray at first, maturing pinkish-grey, with scattered fine pubescence. The cones are 4–7 cm (1.6–2.8 in) long and 1.5–2 cm (0.6–0.8 in) broad, dark purple-blue before maturity; the scale bracts are long, green or yellow, and emerge between the scales in the closed cone. The winged seeds are released when the cones disintegrate at maturity about 5–6 months after pollination.
II. How to Grow and Care
Sunlight
The korean fir does well in many different light conditions, from full sun to partial shade, although a minimum of four hours of sunlight a day is preferable. This tree enjoys direct sunlight unless temperatures are too high – this is because the korean fir prefers a cooler climate.
Ideally, avoid placing your korean fir in full shade because this could affect its rate of growth. Mature trees will cope with full shade a little better, and there are some variants that prefer this environment, but this is usually not recommended for optimal growth.
Temperature and Humidity
Although Korean firs tolerate heat and humidity better than many other fir species, they still prefer a cool, temperate climate. They also can handle some wind but should be sheltered from strong drying winds.
Watering
Water more regularly in the summer, as the korean fir requires moist soil; this is particularly important in the first two years after planting. Though frequency will depend on your climate, a good rule of thumb is to water twice a week during the summer months. However, allow the top layer of soil to slightly dry out between waterings to ensure that your tree does not become waterlogged. Watering once a week during spring and fall should be sufficient, but be mindful of both your climate and the level of moisture in the soil. Cease watering when it rains and do not water in the winter.
Soil
The optimum soil for your korean fir would be a sand or loam soil that is well-draining, with a pH value of 6-6.5 (so slightly acidic). While the soil should stay moist and not dry out for long periods, try to avoid clay soil – this compacts easily and does not drain well, resulting in your korean fir becoming waterlogged.
Fertilizing
It is not always necessary to fertilize your korean fir – if your soil is rich in nutrients, you won’t need to fertilize your tree at all. Otherwise, apply a mulch to your korean fir in either the spring or early summer to aid your tree’s growth and help the soil to retain more moisture as the weather gets warmer. You may also choose to sprinkle a granular, slow-acting fertilizer on the soil under the foliage at the beginning of fall. Use sparingly and make sure that it does not come into contact with the trunk or foliage.
Planting Instructions
Depending on the variety, the korean fir can reach up to 100 m in height, with its foliage extending to around 10 m. The trunk can grow to a diameter of 4 m, so it is essential to give your trees enough space when planting – keep them about 20 m apart.
plant your korean fir in late fall or winter, once the tree is dormant. Choose a day when the ground is not too waterlogged or frozen and plant in an area that is sheltered from the wind, with fertile, well-draining soil. Dig a hole that is slightly wider than the root ball and just deep enough to cover the roots, before filling the hole with soil and watering generously.
If there is a risk of high winds, you may wish to stake your korean fir to reduce the risk of the tree getting blown over. Finally, spread a 8 cm thick layer of mulch around the base of the tree, around a 51 cm radius, to promote healthy growth. Leave a small gap of 8 to 13 cm around the trunk to allow for some water to evaporate.
Keep the soil quite moist for the first few weeks after planting to help your korean fir become established.
Pruning
The korean fir is a very low maintenance tree and requires little pruning. Other than for aesthetic purposes, the primary need for pruning is to remove dead, damaged, or diseased branches. The best time to prune is in late winter or early spring, just as the tree comes out of its dormant state – this can encourage new growth.
When pruning, focus on removing branches that are growing at a strange angle and rubbing against other branches, as this friction can become an entry point for disease. This is best done in a period of dry weather, but if this isn’t going to be possible for a while, it is best to deal with the problem a little sooner, regardless of the weather. Once you have removed problem branches, burn them instead of placing in a compost bin, as this can spread potential diseases.
Propagation
Firs can be rooted from branch cuttings but it is a very slow and unreliable process that isn’t practical for garden propagation. Propagating any fir from a cutting requires patience so if you are up for the challenge to do so at home, take these steps:
- Take a 6- to 8-inch cutting with a sterilized cutting tool. Take a softwood cutting in the late spring or hardwood in the late fall.
- Remove the needles and dip one end into rooting hormone.
- Put the cutting down 3 inches into a pot filled with a moistened mix of perlite, sand, or peat moss.
- Place a clear plastic bag over the pot to keep it warm but cut a couple of small holes for some air circulation.
- Put the pot in warmth and indirect sunlight.
- Mist or water the pot frequently but do not overwater.
- When the seedling is an inch tall, put it in regular potting soil to root; softwood roots faster than hardwood (which can take months).
- Keep the plant in a pot for at least a year before transplanting it into the ground.
How to Grow Korean Fir From Seed
In the commercial trade, Korean firs are normally propagated by professionally grafting branches onto a rootstock of a different species. However, grafting successfully is too specialized for most home gardeners, so the most practical approach is to grow a Korean fir from seeds—a slow process but one that is relatively easy and may be slightly more successful than propagating with cuttings. Here’s how:
- In the fall, as the cones begin to dry and the scales separate, pick some large, ripe cones and place them in a dish in a warm location. As the drying continues, the small seeds inside the cone should dry and drop into the dish.
- Stratify the seeds by soaking them overnight, then place them in a container filled with damp peat moss in the refrigerator for one to four months.
- Plant the stratified seeds at a shallow depth in small containers filled with a mixture of peat moss and perlite or vermiculite.
- Place them in a bright location at 60 to 70 degrees Fahrenheit and keep the growing medium damp until the seeds sprout.
After several weeks, when the seedlings begin to send out true needles, carefully transplant them into larger containers filled with garden soil and well-decomposed compost.
Grow them in a sunny location through the spring and summer until well established. During this time, feed them twice a month with diluted organic fertilizer.
Plant seedlings in the landscape in the fall when they are 1 to 2 feet tall. In some cases, this may involve allowing the tree a full two years in the pot before it is transplanted into the landscape.
Potting and Repotting
Smaller cultivars of Korean fir can make excellent potted trees—they are especially popular as living Christmas trees.
Choose a large pot—at least twice the width and depth of the root ball of your tree. The larger the pot, the less frequently you will need to repot. As a growing medium, a mixture of 1 part perlite or vermiculite with 2 parts compost works well. Ordinary commercial potting soil is also fine. You may be able to grow this slow-growing species for four or five years in the same pot before it becomes root-bound and needs to be repotted. If it becomes too big and cannot be easily moved in and out of your home, it’s best to remove it from its pot and plant it as a permanent landscape tree.
When grown as a living Christmas tree, a Korean fir can be kept outdoors as a potted above-ground plant for the rest of the year. For a week or so before moving it indoors, shift the potted fir to a sheltered, somewhat warmer location, such as an enclosed garage or porch to acclimate it to warmer indoor temperatures. Keep it well-watered and just before moving it indoors, spray the tree with an anti-desiccant, which will preserve moisture in the needles.
Avoid putting the tree in an indoor location near sources of heat and keep the soil moist at all times. Within a week after the holidays, move the pot back outdoors.
Overwintering
Provided your climate zone is appropriate, fir trees planted in the landscape require little extra winter protection. Winter burn is less likely for this tree than for other conifers. But it’s a good idea to make sure the tree is well watered in the weeks leading up to winter frost.
In colder regions, a potted tree will have its roots quite exposed to winter temperatures, so take precautions to place the tree in a sheltered location and wrap the sides and bottom of the pot with insulating material, such as bubble wrap. Don’t keep the potted tree on a paved surface, as stone or concrete surfaces will quickly conduct cold up into the tree’s roots.
Some gardeners bury potted trees up to the top rim of the pot for the winter or heap dense compost around the pot to guard against temperature fluctuations.
Pests and Diseases
Common Pests and Plant Diseases
These trees don’t have serious issues with pests or diseases, though they don’t do well in areas with high air pollution. They can be susceptible to certain insects, including aphids and adelgids. If these insects are present, the tree’s needles might turn yellow or drop off. Forcefully spraying the needles with water to dislodge the insects every other day or so is a natural way to get rid of them. You also can apply insecticidal soap or horticultural oil, though this can discolor foliage. It’s important to remove and replace any mulch around your tree each spring to prevent any dormant insect pests from returning and infesting the tree.
A variety of fungal diseases are possible with Korean fir:
- Root rot: This can occur with trees that are planted in dense, wet soil. Once severe root rot sets in, your tree probably won’t be salvageable.
- Needle rust: It can begin with small white pustules on the lower surface of the needles, then cause the needles to turn yellow and fall off. Viewed from a distance, the tree will appear to gradually turn yellow. There is no effective treatment for fir needle rust, but because this fungus requires fern as a second host to complete its life cycle, removing ferns in the area often prevents the disease from returning.
- Twig blight: This causes branches to die back, beginning at the tips. Lower branches are usually affected first. Have the fungus diagnosed by a local arborist or university extension service, then apply the recommended fungicide. Keeping trees healthy will usually prevent this disease.
Common Problems
In addition to the pest and disease issues common to this species, keep an eye out for these issues:
Yellowish Needles
If your tree seems to be more yellowish than is usual for Korean firs, it may be because the soil is too alkaline, which prevents the tree from properly absorbing soil nutrients. More frequent feeding with an acidifying fertilizer may help your tree, or you can try amending the soil with acidifying organic material, such as pine needles. Yellow needles may also indicate a case of needle rust or a pest infestation.
Brown Branches in the Spring
When the branches on your Korean pine turn brown in spring, at the very time you’re expecting fresh green growth, it usually means your tree has experienced winter burn from cold, dry, winter winds. This often occurs if you live in a borderline zone—the northern part of zone 5 or northward. Young trees can sometimes be protected with a loose tent or shelter made from burlap, but this is an unattractive solution; the better solution is to opt for a species more reliable for your climate.
III. Uses and Benefits
The Korean Fir is also an emerging and popular choice as a Christmas tree, due to its conical shape and pyramidal habit and is cultivated for its attractive foliage and cones. The branches grow out horizontally and are very evenly spaced while the needles are dark green on the upper surface and whitish on the underside. The cones are cylindrical and violet-blue and grow to about 8cm in length and make a very attractive sight.
