Carpinus

( kar - PYE - nus )

At-A-Glance Information

Commonly called Hornbeam, this genus of hardwood deciduous trees has a variety of sun exposure needs and requires regular water for best performance. They will attract birds to the garden, and are long-lived shade trees that will grow at a slow to moderate rate. Leaves have sawtooth edges and are green, turning bright yellow, orange and red when cooler weather rolls around in fall and early winter. These trees are native to temperate regions of the Northern Hemisphere, with the greatest number of species occurring in East Asia (particularly China). Use these trees as specimen plantings, street trees, as spring and summertime shade trees, or plant in rows to create privacy screening. Mature trees rarely need to be pruned, making them great, low-maintenance garden trees.

Carpinus Species and Varietals

The genus Carpinus includes between 30 and 40 species and is a member of the plant family Betulaceae. making them relatives of Alders, Hazels and Birches. Hornbeam growing zones vary depending on the species; for more information, see the descriptions below. To find your zone, click here: Zone Map.

Carpinus betulus (European Hornbeam, Common Hornbeam, Yoke Elm)
Native to Europe through to Iran, this dense, pyramid-shaped tree does best in USDA hardiness zones 4-8 or Sunset growing zones 2-9 and 14-17. It can reach 40 feet tall and just as wide, with drooping outer branches and grey bark. Fall color is yellow and red. Best when grown in full sun but can tolerate light shade if necessary, and can be clipped into a hedge or screen if desired. This species is subject to scale infestation.

'Fastigiata'
With an oval-vase shape at maturity.

'Frans Fontaine'
Narrow tree that reaches 35 feet tall and 15 feet wide.

'Emerald Avenue'
Upright habit with heat resistance. Good as a street tree.

Carpinus caroliniana (American Hornbeam, Blue-Beech, Ironwood, Muscle-Wood, Muscle Beech)
American Hornbeam grows well in USDA hardiness zones 3-9 or Sunset growing zones 1-9 and 14-17 and is native to eastern areas of North America. This species forms a rounded crown and has smooth blue-grey bark. Leaves are green and turn reddish or yellow in fall. These trees can reach 25-30 feet tall and just as wide, with either a single trunk or multiple trunks. They can be grown in full sun to heavy shade. Variety 'Native Flame' has red fall foliage.

Carpinus japonica (Japanese Hornbeam, Kuma Shide)
These trees are endemic to Japan, but are widely grown around the world as garden ornamentals. Japanese Hornbeam reaches between 39 and 49 feet tall when mature, and produces dark green, glossy, slender leaves. Catkins emerge green and age to brown. These trees grow well in USDA hardiness zones 4-9 or Sunset growing zones 1-9 and 16-22.

Carpinus laxiflora (Aka-Shide, Loose-Flower Hornbeam, Loose Flowered Hornbeam)
These trees are native to the Korean Peninsula and Japan, where they prefer to grow in forested mountain regions. They typically reach between 33 and 50 feet tall when mature, and are sometimes used as bonsai subjects or street trees. The straight species is somewhat rustic-looking, but there is a weeping-habit variety available under the name 'Pendula', as well as a variegated form, 'Variegata'. These trees grow well in USDA hardiness zones 5-9 or Sunset growing zones 1-9 and 14-17.

Carpinus orientalis (Oriental Hornbeam, Eastern Hornbeam)
This species of Hornbeam is native to Hungary, the Balkans, Italy, Crimea, Turkey, Iran, and the Caucasus. These small trees rarely exceed 33 feet tall and are often seen as multi-trunked shrubby specimens. These trees have gained popularity as ornamentals in the past few years, and are commonly used as bonsai subjects. Oriental Hornbeam grows well in USDA hardiness zones 5-7 or Sunset growing zones A1 and 1-7.

Carpinus tropicalis (Mexican Hornbeam, Tropical Hornbeam, Alisillo, Capillero, Mora Blanca)
Native to Mexico, El Salvador, Guatemala, Honduras, and Nicaragua, this species can reach up to 98 feet tall when mature, though is commonly seen at lower heights. These are classic cloud forest trees, and appreciate wooded environments. This species does best in tropical moisture and heat, growing well in USDA hardiness zones 9 or 10.

Carpinus turczaninovii (Turczaninow Hornbeam, Korean Hornbeam, Rock Hornbeam)
These trees are native to China, the Korean Peninsula, and central to southern areas of Japan. This species forms a shrub or small tree that rarely exceeds 15 to 20 feet tall. These trees can take very hard prunings, and are fantastic subjects for bonsai projects. Turczaninow Hornbeam grows well in USDA hardiness zones 5-8 or Sunset growing zones A1 and 1-7.

Caring for carpinus

Hornbeam trees vary in their sunlight needs depending on the species grown. Check requirements before planting to ensure that trees are getting the sunlight they need to grow well. Carpinus trees prefer well-draining soil, but they can adapt to a variety of soil types, including clay, loam, or sandy soils. They thrive in slightly acidic to neutral pH levels. If soil is particularly poor and does not drain well, amend with organic matter or sand before planting to ensure success. Mulch around the base of the plant after installation to suppress weed growth and maintain soil temperature and moisture. When newly installed and for the first year or two afterwards, these trees appreciate regular waterings, especially during drier periods of the year. Once established, these trees are considered to be somewhat drought-tolerant, and benefit from occasional deep waterings during prolonged dry spells. For best performance and health, however, keep soil consistently moist (but not waterlogged). These trees should be putting on between 12 and 24 inches of growth per year in ideal growing conditions.

Prune Hornbeam trees in late winter or early springtime, just before new growth starts to push out for the year. These trees respond well to pruning, and can be shaped as hedges, screening plants, or as standalone trees. Regularly remove deadwood and diseased or crossing branches to maintain the tree's health and shape. These trees do not commonly need fertilizing, but if they seem to be struggling or soil is particularly poor, they may benefit from a yearly feeding with compost applied around the base of the tree. Hornbeam trees can live for hundreds of years in the landscape before they need to be replaced.

Propagation

Carpinus can be propagated either by using cuttings or from seed. To ensure that your propagated plant will have the exact same qualities and characteristics as the parent plant, use the cutting method. If you would like to experiment and see what plant you can grow from seed, just keep in mind that it will not necessarily be the same as the parent plant. To propagate your Hornbeam, follow the instructions below:

Propagating Carpinus by Cutting

Gather your materials. You'll need a clean, sanitized, sharp pair of garden shears, rooting hormone, a pencil, and a 3-inch pot filled with well-draining compost or other organic material. A good substrate for propagation of cuttings is a light blend of 1/3 pasteurized soil or compost, 1/3 sand, vermiculite or perlite, and 1/3 coconut coir or peat moss.
In spring or early summertime, choose the plant that you'd like to propagate. Ensure that this plant has had a good watering the night before, as this will improve the chances your cutting will take root. Cut one or more 6 inch portion(s) of the end of a non-blooming branch and strip the leaves off of the lower half. Make a hole in your planting medium by pushing your pencil into the soil. Dip the end of the stem in rooting hormone, and plant it in your pot. Fill in soil around the cutting to support it, but do not pack it down too much.
Moisten with water, and ensure that the pot has good drainage. Your pot should be kept in warm, sunny conditions indoors (and not in direct sunlight). Water whenever your soil is dry under the top layer. After about four to six weeks have passed, your cutting should be rooted. When you notice new growth, you'll know you have roots.
Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 55 and 70 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring, when you can transplant it to its new home. Ensure that the last frost of the year has occurred before doing this, as it can seriously damage your new shrub.

Propagating Carpinus by Seed

Keep in mind that the plant you get from seed will not necessarily mimic all of the characteristics of the parent plant. To propagate by seed, you will need a paper bag, a pot or tray filled with well-draining compost or other organic material, a spray bottle and a fork. The best potting medium for seed germination is a light blend of 1/3 pasteurized soil or compost, 1/3 sand, vermiculite or perlite, and 1/3 coconut coir or peat moss.
Harvest your seeds in late summer or fall. The seed pods on Carpinus plants are pretty easy to spot, they're large and dangle from the branches in bunches, left behind after flowers have faded. Once they have dried out and begun to split open, you can harvest the seeds inside. Cut them off of the plant, placing them in a paper bag. Harvest as many as you can, and place the paper bag in a dry, cool, dark area. They will begin to split open and release the seeds contained inside. Once they have been released, take them out of the bag and put them in a container so you can work with them.
Carpinus seeds have a hard coating that protects them, but this coating also makes it a little difficult to get them to germinate. We can help the process along by scarifying them with sandpaper (or simply rubbing them against an abrasive surface). Do this with as many seeds as you can; they will probably not all sow, and the ones that do will be of varying characteristics. The more seeds you plant, the more chances you will have to get the resulting shrub you want. Place your seeds in lukewarm water for six hours. Viable seeds will sink to the bottom, and non-viable seeds will float to the top. You can discard any seeds that float.
Water your prepared seed tray or pot filled with soil, and ensure that good drainage is occurring. Place your seeds in your prepared pot or seed tray about a quarter inch to a half-inch under the soil surface. Cover them with soil and water with your spray bottle. Place your tray of seeds in a warm area that receives bright, indirect light. A greenhouse is the most ideal climate, but a planting tray inside a window will do as well. Germination usually takes 7-14 days from sowing. Once you begin to see seedlings sprout and they are able to be handled, transplant them to their own individual 3-inch pots, filled with the same potting medium as described in Step 1. Loosen the seedlings from the potting medium by digging down with the tines of your fork about an inch and a half, gently working the seedling up until it is out. Then, replant the seedling in its individual pot.
Keep the seedling's potting medium moist, but not wet, by spraying the soil with your spray bottle. Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 55 and 70 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring (after the danger of frost has passed), when you can transplant it to its new home.