Extension Service: New live-oak cultivar tackles its size issue

Although our Southern Live Oaks (Quercus virginiana) held up pretty well in Hurricane Wilma, some need to be replaced because they were so battered that they became hazard trees.

At the same time, future communities are developing landscape plans with uniformity of tree shape in mind. Anyone who has closely scrutinized more than two live oaks will observe that uniformity in texture and shape is not common with this species. Outside my office door, we have a parking lot full of live oaks that vary in form and structure, from almost weeping to robust upright to a messy quagmire of witches’ brooms — a horrible array of crossing branches. As is typical, there are multiple leaders, which makes for weak branch attachment.

Cultivars of a plant species are valued because they insure uniformity and eliminate some of the unruly plant growth variations inherent in many seedling-grown plant species such as Southern Live Oaks. Several new cultivars have been developed by Tree Introductions ( www.treeintroductions.com/ )in Athens, Ga. A “chance” (read “golden opportunity”) seedling growing in a production field in 1988 caught the eye of Tommy Strickland of Future Trees, Inc. in Statesboro, Ga. This “chance” seedling became the source for plant patent # 11219, the “Highrise” live oak that is a breakthrough for expanding live oak use in the landscape.

“Highrise” has a strong upright leader, a pyramidal form resembling a fine-textured pin oak, and reportedly requires less pruning than the unruly seedling sources of live oaks. “Highrise” has a low spread-to-height ratio. This means that, compared to a typical, wild live oak which can reach 60 feet in canopy width and 40 feet in height, a “Highrise’” will be only about 25 feet in width and 40 feet in height.

The large spreading canopy is one of the limiting factors in using live oaks in smaller yards and neighborhoods. However, don’t forget the aggressive root system; be forewarned that there should still be about the same root spacing as with typical live oaks, which is about 8 to 10 feet between curb and sidewalk. This reduces the chances for roots to cause lifting of sidewalk slabs 10 years down the road.

There are several other live oak cultivars, such as “Cathedral” and an earlier “Millennium.” These have a uniform growth habit, but are wider-spreading than “Highrise.”

One would think that these vegetative-derived (stem cuttings) cultivars would be double or triple the cost of a plant produced from an acorn thrown in a can. Costs from Southern Pride Tree Farm west of Ocala are about $275 for a Florida No. 1 grade, 4-inch trunk caliper, while the same grade and size “Highrise” is about $320.

It’s a pretty good deal for a plant which renowned plant guru Michael Dirr describes thus: “ ...embodies the noble characteristics and cultural adaptability of the traditional live oak in a more restrained, elegant form that is suitable for planting in restricted growing areas.”

Web site for the farm is: www.sptreefarm.com/About%20Our%20Trees.htm

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Doug Caldwell is the commercial landscape horticulture educator with IFAS (Institute of Food and Agricultural Sciences) of the University of Florida Collier County Cooperative Extension Service. For updates on Southwest Florida horticulture and more landscape information, call the Master Gardener Plant Clinic, 353-2872 or visit: collier.ifas.ufl.edu org.

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