If you’ve never heard of sourwood trees, you have missed out on one of the most beautiful native species. Sourwood trees, also called sorrel trees, offer delight in every season, with flowers in summer, brilliant color in fall, and ornamental seed pods in winter. If you are thinking of planting sourwood trees, you’ll want to learn more sourwood tree information. Read on to learn about the planting and care of sourwood trees.
| Common name | Lily of the Valley Tree, Sorrel Tree, Sourwood |
| Botanical name | Oxydendrum arboreum |
| Family | Ericaceae |
| Species | arboreum |
| Origin | Eastern and southern United States |
| Life cycle | Perennial |
| Plant type | Native Plant |
| Hardiness zone | 5, 6, 7, 8, 9 |
| Sunlight | Dappled Sunlight |
| Maintenance | Low |
| Soil condition | High Organic Matter |
| Soil ph | Acid |
| Drainage | Well-Drained |
| Growth rate | Slow |
| Spacing | 12 – 24 ft. |
| Harvest time | Fall |
| Flowering period | Summer |
| Height | 2- 30 ft. |
| Width | 2- 30 ft. |
| Flower color | Cream, Tan |
| Leaf color | Gold, Yellow |
| Fruit color | Brown, Copper |
| Stem color | Brown, Copper |
| Fruit type | Capsule |
| Fruit benefit | Showy |
| Leaf benefit | Showy |
| Flower benefit | Fragrant |
| Garden style | Butterfly Garden |
| Uses | Coastal |
I. Appearance and Characteristics
Oxydendrum arboreum, the sourwood or sorrel tree, is the sole species in the genus Oxydendrum, in the family Ericaceae. It is native to eastern North America, from southern Pennsylvania south to northwest Florida and west to southern Illinois; it is most common in the lower chain of the Appalachian Mountains. The tree is frequently seen as a component of oak-heath forests.
The bark is gray with a reddish tinge, deeply furrowed and scaly. Branchlets at first are light yellow green, but later turn reddish brown. The wood is reddish brown, with paler sapwood; it is heavy, hard, and close-grained, and will take a high polish. Its specific gravity is 0.7458, with a density of 46.48 lb/cu ft.
The winter buds are axillary, minute, dark red, and partly immersed in the bark. Inner scales enlarge when spring growth begins.
Leaves are alternate, four to seven inches long, 1.5 to 2.5 inches wide, oblong to oblanceolate, wedge-shaped at the base, serrate, and acute or acuminate. Leaf veins are feather-veined, the midrib is conspicuous. They emerge from the bud revolute, bronze green and shining, and smooth; when full-grown, they are dark green, shining above, and pale and glaucous below. In autumn, they turn bright scarlet. Petioles are long and slender, with stipules wanting. They are heavily laden with acid.
In June and July, cream-white flowers are borne in terminal panicles of secund racemes seven to eight inches long; rachis and short pedicels are downy. The calyx is five-parted and persistent; lobes are valvate in bud. The corolla is ovoid-cylindric, narrowed at the throat, cream-white, and five-toothed. The 10 stamens are inserted on the corolla; filaments are wider than the anthers; anthers are two-celled. The pistil is ovary superior, ovoid, and five-celled; the style is columnar; the stigma is simple; the disk is ten-toothed, and ovules are many.
The fruit is a capsule, downy, five-valved, five-angled, and tipped by the persistent style; the pedicels are curving.
II. How to Grow and Care
Sunlight
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 incredibly 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.
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.
Watering
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.
Soil
Your sourwood tree prefers acidic, organically rich, moist, well-drained soils. Again, its native habit will inform you greatly of 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.
Fertilizing
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.
Planting Instructions
It’s best to buy a smaller sapling because larger trees are trickier to transplant. Be sure to site the tree where you want it because sourwoods don’t like to be moved after being planted.
Plant while the tree is dormant—in spring before new growth emerges or in fall after leaves have dropped. If your soil needs any amendments, such as organic matter or a soil acidifier) mix these in before planting. Dig a hole about a foot wider and the same depth as the root ball, and mound some soil in the center of the hole.
Examine the roots and remove any that appear damaged. Set the tree in the hole on top of the center mound and spread the roots out evenly. Gradually backfill with soil, tamping it down and watering to settle it around the roots as you fill the hole. When you finish backfilling, the tree should sit slightly higher than it did in the pot. Apply 3 or 4 inches of organic mulch around the planting area, but keep the mulch a few inches away from the trunk of the tree. Water the tree thoroughly.
Pruning
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.
Propagation
The best method of propagating sourwood is by seed, and it requires a lot of patience. Cuttings are notoriously difficult to root. The seed is tiny and must be collected in the fall from the ripened seed capsules. Sow it in acidic soil, such as a mixture of peat moss and sand, and keep it consistently moist, either under mist or in a plastic tent. Subjecting the seed to a period of cold temperatures (known as stratification) for a couple of months may hasten germination. It will be several years before the seedlings are large enough to transplant into the garden.
Transplanting
The ideal time to transplant common sourwood is generally in the late winter to early spring (S2-S3) period when the plant is dormant. This mitigates transplant shock and gives common sourwood ample time to establish before the growing season. Ensure a location with well-draining soil and partial to full sun. If needed, acclimate the plant gradually before transplanting to reduce stress. Remember, transplant success depends on mimicking common sourwood’s natural conditions as closely as possible.
Pests and Diseases
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.
III. Types of Sourwood Trees
Sourwood is the only species in the genus Oxydendrum, and there are only a few named varieties.
- Albomarginatum
Oxydendrum arboreum ‘Albomarginatum’ sports green leaves with white margins. Some leaves are marbled with white. Its fall color is spectacular.
- Chameleon
‘Chameleon’ is a rare cultivar that grows with a more upright and conical habit than the other species. Its fall foliage shows color early as it morphs into bright shades of yellow, red, and purple, all at the same time or in sequence.
- Mt. Charm
This cultivar has a symmetrical, conical habit. It is the earliest sourwood tree to display brilliant fall foliage color.
IV. Uses and Benefits
- Ornamental uses
Common sourwood is a common, compact flowering tree grown in both public and private gardens for its lovely seasonal appearance and manageable size. Common sourwood can be used as a specimen piece for its late-blooming flowers and stunning fall foliage, or simply as a lawn tree for the useful shade it provides. It makes a great feature in shade or woodland gardens. Azaleas and rhododendrons are great companions to plant near common sourwood.
- Other uses
The leaves are also a laxative.
Sourwood is renowned for the honey that bees produce from the nectar of its flowers. Juice from its blooms is used to make sourwood jelly. The shoots were used by the Cherokee and the Catawba to make arrowshafts.
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