How to Grow and Care for Bur Oak

Bur oak is a slow-growing, long-lived native oak tree that reaches 90 feet tall and wide. It is identified by its dull green 8-inch oblong leaves with 7 to 11 lobes, hairy yellow-green undersides, and corky twigs. It has deeply ridged gray bark with deep furrows that become more distinct with age. Bur oak grows best in full sun with at least six hours of sunlight, handling many soil types, and is one of the most cold-tolerant oaks. 

Bur Oak Care

To successfully grow a bur oak, make sure that there is sufficient space, both for the tree's significant height and width and for the roots. Bur oaks have a deep taproot, and their expansive roots grow more deep than wide. They are less likely to damage sidewalks, though they still could because their absorbing roots occur in the top 12 inches of soil.

Here are the main care requirements for growing a bur oak:

• Plant in a full sun location.
• Handles many soil types and pH levels—sand, salt, clay, alkaline, acidic, and neutral.
• Needs regular watering until established; long taproot helps it become drought resistant.
• Withstands high temps and humidity in summer and subzero winters.
• Keep away from salt spray or rock salt.
  

Light

Bur oak prefers full sun with at least six hours of direct light.

Soil

The tree can adapt to many different soils in terms of texture and structure. It grows in sand, silt, and clay and can withstand compacted soils and poor drainage.

Occasional flooding of the planting site is not a problem. However, the tree won’t do well when there is repeated and extended flooding, especially during the growing season.

Water

A newly planted bur oak must be watered deeply and regularly for at least two years after planting. In the absence of rain, continue to water the tree during the third year to ensure it develops a strong root system.

Once the tree is established, it is drought-tolerant thanks to the taproot that allows it to draw water from deeper soil layers.

Temperature and Humidity

Bur oak is well-adapted to the continental climate of its native range with its humid summers and subzero winters. The tree can be found as far north as Nova Scotia and down to Texas. It is one of the most cold-tolerant oak species. 

Fertilizer

If, at planting time, the soil is amended with organic matter, or the tree starts in soil with a good nutrient balance, bur oak does not need extra fertilizer. A high-nitrogen fertilizer will harm the tree.

Types of White Oak Trees

A bur oak's native habitat is moist woodlands, bottomland forests, prairies, and sandhills. Bur oaks (Quercus macrocarpa) are a member of the white oak group of trees. Bur oaks share the same characteristics as other white oaks, including rounded lobes on the leaves and producing acorns (fruits) that mature in a single season and sprout soon after they fall in autumn.

Other white oak trees include:

• White oak (Quercus alba): Grows 60-100 ft. tall; 50-90 ft. wide
• Chinkapin oak (Quercus muehlenbergii): Grows 50 to 80 ft. tall; 50 to 70 ft. wide
• Swamp white (Quercus bicolor): Grows 50 to 70 ft. tall, 50 to 70 ft. wide
• Post oak (Quercus stellata): Grows 40 to 50 ft.; 35 to 50 ft. wide
  

Pruning

Bur oak should be pruned in late fall or early spring. Start by removing dead, diseased, or damaged branches at the base or where they meet a lateral branch. Cut off any branches that grow downward or those that are rubbing together. You can prune out up to 1/3 of the branches in a season to open the canopy and allow better sunlight and air circulation.

Propagating Bur Oak

While growing an oak from acorns is the most common route, you can also propagate bur oak from cuttings. Here's how:

1. With sharp, clean pruners, take several cuttings from hardwood, each at least 6 inches long, from stems at least the diameter of a pencil. The cutting should have at least three or four nodes.
2. Snip the leaves off the bottom, leaving only a few at the top. Make a fresh, sharp cut at a 45-degree angle on the bottom of the cutting,
3. Dip the cut end in rooting hormone and plant it in a container filled with potting soil made of peat moss and perlite.
4. Keep the soil moist and the humidity high by wrapping a clear plastic bag loosely over the cutting. Place it in a warm area until roots form, which might take two or three months. Keep in mind that not all cuttings will "take" and grow—don't be disappointed if you lose several of them.
5. Once roots grow, put the tree indoors in a sunny, warm spot for the first year. Then, it is ready to be transplanted into the ground.
   

How to Grow Bur Oak From Seed

If you don’t mind tending to it for a few years before the seedling is large enough to be transplanted, you can grow bur oaks from acorns. Inspect the acorns for cracks and holes and choose only fully intact ones. To grow seedlings, follow these steps.

1. Soak them in water for 24 hours, which helps you identify hollow ones that float on top. These should be discarded. Remove the caps if they haven’t fallen off on their own yet.
2. Fill a 1-gallon planting container with a drain hole with the same soil as the location where you intend to plant the tree. Mix in about one to two trowels full of organic matter or compost.
3. Place two to three soaked viable acorns in the container, laying them on their sides. Cover with 1 to 2 inches of soil.
4. Water regularly and deeply. The acorns will start to sprout in about one month.
5. Once the seedlings emerge, only keep the strongest one and gently pull out the others with their acorn. Protect the young roots from root burn by shielding the exterior of the container from the sun, either with wood, heavy fabric, or a second, larger pot.
   

Potting and Repotting Bur Oak

When starting a bur oak from an acorn, use a 1-gallon container with good drainage. The container might seem much too large at first, but remember that bur oaks are finicky to transplant because of their taproot. You want to avoid transplanting the seedling to a larger pot when it outgrows the original one.

Overwintering

These very cold-hardy trees can tolerate freezing temperatures in their usual growing zones. Young trees still in containers or newly planted can benefit from a layer of mulch or straw over the roots.

Common Pests and Plant Diseases

The bur oak is affected by the same pests and diseases common among oak trees in the Northern Hemisphere. Some of these include oak-leaf blister, which looks like small white blisters on the leaves in midsummer, and leaf spot, which creates small black or brown spots on the leaves.

Bur oak blight is a fungal leaf disease that causes leaf browning and leaf loss in late summer and early fall, only affecting the small-acorn variety of bur oak. These three fungal diseases can be treated with a fungicide.

A white-rot fungal disease, sometimes known as canker, can affect the trees as well—and in this case, there isn't much you can do. Removing the tree before the fungus affects other plants nearby is the best treatment.

Various pests make their home in bur oaks, such as caterpillars, oakworms, and scale. Introducing ladybugs into the landscape can help control the issue, as can removing caterpillars by hand. Using an insecticide is a last-ditch effort but often works, especially for immature trees.

Common Problems with Bur Oak

Bur oak trees are easy to grow in many soils, withstanding temperature swings and adverse conditions.

Growths on Bur Oak

Oak trees quite commonly develop lichen, which appears as a gray or green growth on a tree's trunk or larger branches. Lichen can develop at any point during its lifespan and is not a health indicator. Lichens don't cause a problem and can be left alone.

Mistletoe is a parasitic plant that often attaches to oak trees. You can spot mistletoe because it remains green in the winter, long after the bur oak has dropped all its leaves. To control mistletoe, cut the affected limbs from the tree at least 1 or 2 feet below where the mistletoe is attached. Large infestations might require the use of chemicals designed to attack mistletoe.

Tree Isn't Producing Acorns

It might not be old enough if your bur oak tree does not produce acorns. The bur oak is a slow-growing, long-lived tree that must be at least 35 years old before it has viable acorns.