Quercus dentata 'Pinnatifida' - Cut-leaf Japanese Emperor Oak

***Please note that this tree is very hard to find.  Although we carry it when available, you may see it often out of stock. *** 

Picturesque and attractive in habit and form, oaks make great focal points and specimens. They naturally and effectively anchor our manmade landscapes to the land. When sited properly, they buffer our homes and buildings from harsh winter winds and shade them from brutal summer heat. Most oaks are adaptable and extraordinarily resilient. Some are tolerant of extremes. Here at the nursery, it's rare for them to need warranty replacements.

In Pennsylvania and the Mid-Atlantic region, there are 20 or so native oak species. In nurseries, including ours, you’ll usually find even more, as well as various hybrids and cultivars. Because of this, there's an oak for almost any outdoor space.

Japanese Emperor oak (Quercus dentata), also known as Korean oak, has a wide native range in East Asia residing in and along moist woodlands and forests. Countries in this distribution include China, Taiwan, Mongolia, Korea, and Japan. Leaves on this oak are particularly large, especially when planted in areas with plentiful moisture and protection from wind (although those aren't necessary conditions). The bark becomes especially cracked and ridged at a young age, making young trees appear old and stately. Long, pendulous catkins emerge in spring before foliage, providing unique spring interest.

Quercus dentata 'Pinnatifida' is a variant with deeply dissected and somewhat leathery leaves. This is probably the most unique oak we carry and definitely one for tree collectors. From being outside its natural range and its leaves being akin to filigree (rendering less photosynthesis), the growth rate of this tree is fairly slow. Expect 1' a year or less and a mature size being around 20' high and wide.

Check out the specimen we planted from a #20 container in 2019 behind the pavilion - very close to the store (the tree is on the right side of the store if you're facing it from the front).

Most oaks practice "marcescence" which means young trees don't drop their leaves till new leaves emerge in spring. On older trees, leaves on the bottom of the crown hold till spring while leaves higher up drop in fall. One theory that explains this phenomenon is it helps protect buds from herbivory. Regardless, this phenomenon adds winter interest to the tree by way of texture, color, and the sound of rustling leaves. If planted in a very windy area such as our Japanese Emperor oak, however, leaf drop may happen in fall.

Oaks don't produce copious amounts of acorns annually. Instead, they choose to produce large quantities once every 2-5 years (provided they are pollinated by other oaks). Years of heavier acorn production are called "mast years." Oaks usually don't produce significant acorns until they're a couple decades old. While some see acorn production as a nuisance, we encourage you to think of it as providing a valuable resource to the animals and ecology of your yard and neighborhood. It's certainly wise, however, to carefully select a good site for any oak or other large tree. Maybe the middle of the lawn is a wiser spot than above the swimming pool, for example. In the case of this cultivar, acorn production is limited due to its smaller size and, most likely, from being efficiently pollinated by our native oaks which are genetically further removed.

For the layman, oaks are generally organized into three categories: red oaks, white oaks, and live oaks. This helps with identification as well as care. Live oaks are typically evergreen that are found further south. All native oaks to Pennsylvania are in the red oak and white oak groups. Japanese Emperor oak is in the white oak group. Species in this group are identified by leaves with rounded lobes, even though Cut-leaf Japanese Emperor oak doesn't resemble that description. They drop their acorns in fall and germinate soon thereafter. Species in the white oak group are also more resistant to introduced pathogens, such as oak wilt and bacterial leaf scorch. More on this momentarily.

Going back to wildlife, the reason oaks are so well utilized is that while oak tannins are bitter, they aren't highly toxic or lethal. This is evidenced by the 500+ species of caterpillars of butterflies and moths that are supported by oaks native to North America. (Remember, if we want pollinators and healthy bird populations, we need caterpillars!). And of course, the acorns are rich in nutrients for mammals and birds. Acorns can be soaked and ground into flour to use in baking as well, with white oak group members having sweeter acorns than the others.

While this species of oak isn't native, it's been observed to be a host plant for beneficial native insects here, notably caterpillars of moths and butterflies. With the filigree-like foliage of this cultivar, however, you may not see much. Any tendencies to naturalize have not been detected and are unlikely.

Despite the wood of oaks being strong, even more so with slow growing oaks, we advise planting most trees the radius of a mature crown away from structures. As this cultivar matures around 20 'wide in most landscapes, we suggest planting this tree no less than 10 feet away from your house. Most oaks are long-lived in the wild, with the Japanese Emperor oak commonly living to 300 years. If planted and cared for properly, we don't see any reason why yours couldn't do the same.

While nevertheless hardy, many oaks in the eastern US have fallen prey to two introduced pathogens in recent decades: oak wilt and bacterial leaf scorch. To reduce the risk of introducing these pathogens into your tree, only prune (if you must at all) during the colder months (November through March). Pruning during the warmer months leave open wounds that run the chance of attracting insects that might transmit these pathogens into the tree’s vascular system. The good news is that species in the White oak group are the most resistant to the worst effects of these diseases.

If deer are a problem for you, we recommend you provide your tree with protection, such as a metal cage, until the tree is large enough to not be severely damaged. Once the tree is tall enough that the cage can be removed, protect the trunk with a trunk protector to prevent damage from buck rub from September through December. Tree guards are usually no longer necessary when the diameter of the trunk at chest height is 5".

Written by Plumline staff and not AI.