January 2019 Articles

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As strong as an oak

As strong as an oak Editor: Rick Bogren at 225-578-5839 or rbogren@agcenter.lsu.edu By Dan Gill LSU AgCenter Horticulturist The oaks have become a part of American culture more than most other types of trees. Oaks are a symbol of strength and durability. Strong as an oak is a common comparison. “From little acorns mighty oaks do grow” is a saying suggesting small beginnings can lead to great things. Oaks are not among the fastest-growing shade trees, but some species grow faster than others. The slower rate of growth has its benefits as it contributes to the strength of the wood and long life of these trees. The water oak, for instance, has a comparatively fast rate of growth. It is undesirable, however, because it has relatively brittle wood that is prone to decay (they frequently blow over in high winds) and a short life expectancy of only around 60 years. People considering planting an oak as a shade tree need to carefully consider the suitable species available and choose the one that best suits the location and role it will play in the landscape. Now is a great time to plant oaks (and other shade trees) in the landscape. Here are some of the choices. Live oak (Quercus virginiana) The live oak is virtually everyone’s favorite oak; indeed, for many people it is their favorite tree altogether. There are certainly good reasons for this. With its lustrous, dark, semi-evergreen leaves and gracefully spreading branches, the live oak is outstandingly beautiful. The live oak is a tough, strong, decay-resistant species that has an exceptionally long life expectancy. It is one of our most hurricane-resistant native trees. Live oaks can live for hundreds of years and grow to be massively large. We are fortunate indeed to live in one of the few places in the world where these amazing trees grow to perfection. Given this, you might be surprised to hear that I’m constantly telling people not to plant them. Did I mention live oaks are huge? At 60 feet, the height is fairly modest for an oak. It is the spread of 75 to 100 feet that is the issue. They are far too large for the typical urban lot. A mature live oak can completely overwhelm a yard and landscape and the neighboring yards as well, casting dense, heavy shade. A live oak’s massive surface root system will readily destroy sidewalks, curbs, driveways and patios if planted too close. Their naturally low, spreading growth habit is totally unsuitable to the typical urban landscape or street planting. (Live oak branches typically sweep down to the ground as the trees age.) As a result, they have to be pruned through time to force them into an unnatural upright shape. Even so, when used as street trees, it is typical to see large, low branches scarred where vehicles have hit them or massive wounds where low, large branches had to be pruned to clear traffic lanes. So, my advice is to love the live oak for the magnificent tree it is, but be careful in considering it for planting in your landscape. Nuttall oak (Quercus nuttallii) and Shumard oak (Quercus shumardii) Two native oak species I’m recommending a lot these days are the Nuttall oak and Shumard oak. These oaks have moderate growth rates — faster than live oak but not as fast as water oak. They live longer (more than 100 years) and are not so prone to trunk rot as water oaks. The Nuttall oak is particularly well-suited to the lowland areas while the Shumard oak is native to more upland sites. Both of these oaks have upright, oval growth habits, about 50 to 60 feet tall and 30 to 40 feet wide, which fit well in urban landscapes. They are deciduous and drop their leaves from late November through early December. Both will achieve some fall color; the Nuttall oak turns a dull yellowish-orange while the Shumard oak turns a more attractive burgundy red. Willow oak (Quercus phellos) The native willow oak is similar in size, shape and growth rate to the last two species. It is an excellent tree for Louisiana landscapes and deserves to be more widely planted. It is an LSU AgCenter Louisiana Super Plants selection. The common name comes from the narrow, willow-shaped leaves. Not only does this give the oak a somewhat unique texture and appearance when compared to other oaks, but it makes the tree one of the neatest trees around. The narrow leaves seem to just disappear when they drop in the fall. So as far as deciduous trees go, this one is less likely to burden you with lots of leaf raking in the fall. This is one of the things I especially like about the willow oak. More to try There are more species of oaks to choose from. Other notable species include Southern red oak (Q. falcata), cherrybark oak (Q. falcata var. pagodifolia), Japanese evergreen oak (Q. glauca, a smaller — 20 feet by 15 feet — evergreen species), cow oak (Q. michauxii, also called basket or swamp chestnut oak) and overcup oak (Q. lyrata). Information on these oaks is available online or in reference books, such as “Southern Plants” by Odenwald and Turner.