How to Grow and Care for Sourwood (oxydendrum arboreum)

The sourwood (often called sorrel) is a pretty little ornamental tree that is perfect for smaller spaces. It is the ideal ornamental tree when it reaches maturity when it can bloom after about its fifth season. Its slow growth rate is appealing as this allows the wood to become nice and strong while staying manageable and making care relatively easy, and the best news is there are no serious pest or disease problems. It makes an excellent specimen or focus of the center of a garden surrounded by native perennials.

Sourwood Care

One of the things that make the sourwood so appealing is the real lack of care that needs to be done to maintain this beautiful ornamental tree. It is not snobby like some ornamentals which require fussing and tending. Its place in the ecosystem as an understory tree really allows it to be the understated underdog while making a visual impression that will be sure to win your heart. The best care you can give it is knowing what it likes and doesn't like.

Light

The sourwood spends most of its time in the understory of the forests, draped in the shade of huge canopy trees like oaks and maples. Because of this, it is adaptable to various light conditions which makes it incredible versatile as invaluable in ornamental horticulture. It will have a slight fall off in fall color and blossoms as a result of not receiving full sun but will still be stunning.

Soil

Your sourwood tree prefers acidic, organically rich, moist, well-drained soils. Again, its native habit will inform you greatly to its preferred environment. The forest floor is covered in fallen leaves, which break down into leaf mold; this is the fungal material of decomposing leaves. While not incredibly high in nutrients, this organic material makes a great soil amendment that the sourwood thrives in naturally.

Water

For an ornamental plant, the sourwood does not have huge levels of thirst. It will take some supplemental watering when extreme dry weather sets in, but it can stand some drought conditions for a time. The main consideration is watering newly transplanted trees in order to get them to establish themselves. Sourwoods are notorious for bad transplanting, so it's vital that you adequately water the newly planted tree. The normal standard of watering weekly for the first two seasons applies, at a rate of two to three gallons a week per trunk diameter measured by caliper at chest height. Once the tree is established you can taper the supplemental watering off and let nature take over.

Temperature and Humidity

Native to the rocky hills and understory of the Appalachians, the sourwood enjoys the cooler weather of the upland eastern seaboard but can also do well as far south as Louisiana. The range of trees does well within its USDA hardiness zone 5-9, but there is little margin for error if you push outside the zone.

Fertilizer

Being a slow-growing tree that takes a bit of time to mature, using fertilizer during the first five years will not do much other than stimulating limb growth. Fertilizing before maturity will create more work for you and weaker wood on the branches. If there are issues with low bloom production, you might consider testing your soil for deficiencies, but until the tree is mature enough to set blooms, time and patience are your best friend.

Types of Sourwood Trees

Unlike most ornamental trees, the sourwood does not have many cultivars. The lack of cultivars is because the nursery trade has raised the breeding stock and found many significant mutations to breed. Even the straight species is difficult to find in the trade without looking for the plant in a specialty store. That being said, here are a few of the rare cultivars to have actually made it into cultivation in the trade:

• Oxydendrum arboreum 'Albomarginatum' - This is a selection with white leaf margins and exceptional autumn color.
• Oxydendrum arboreum 'Chameleon' - Colorful fall foliage display. Displays shades of red, purple, and yellow in fall. Upright habit.
• Oxydendrum arboreum 'Mt. Charm' -Leaves color early and present bright shades. Habit is symmetrical.

Pruning the Sourwood

Pruning the sourwood is a pure joy as it is very slow-growing, and the only worries you should have are pruning the tree for structure and establishing a single leader. Pruning should be done annually in the fall, and you will want to cut the branches to establish a narrow crown on a single slender leader.

Common Pests and Plant Disease

Another reason why the sourwood is so valuable as an ornamental tree in the landscape is because it does get seriously damaged by any insects or diseases that take up residence. Most if not all issues that come up will either resolve themselves or be so minor that they can be overlooked as simply a nuisance.