Swamp Spanish Oak (Quercus palustris)

Oaks, Pin Oak, Swamp Oak, Swamp Spanish Oak

Quercus palustris, colloquially known as pin oak, is a deciduous tree native to North America. Due to its favorable growing qualities and beautiful bronze coloration in autumn, pin oak is one of the most common oak species used in landscaping.

I. Appearance and Characteristics 

Quercus palustris, also called pin oak, swamp oak, or Spanish oak, is a tree in the red oak section (Quercus sect. Lobatae) of the genus Quercus. Pin oak is one of the most commonly used landscaping oaks in its native range due to its ease of transplant, relatively fast growth, and pollution tolerance.

Quercus palustris is a medium-sized deciduous tree growing to 18–22 metres (59–72 feet) tall, with a trunk up to 1 m (3+1⁄2 ft) in diameter. It has an 8–14 m (26–46 ft) spread. A 10-year-old tree grown in full sun will be about 8 m (26 ft) tall. Young trees have a straight, columnar trunk with smooth bark and a pyramidal canopy.

By the time the tree is 40 years old, it develops more rough bark with a loose, spreading canopy. This canopy is considered one of the most distinctive features of the pin oak: the upper branches point upwards, the middle branches are at right angles to the trunk, and the lower branches droop downwards.

The leaves are 5–16 centimeters (2–6+1⁄4 inches) long and 5–12 cm (2–4+3⁄4 in) broad, with five or seven lobes. Each lobe has five to seven bristle-tipped teeth. The sinuses are typically U-shaped and extremely deep cut. In fact, roughly the same amount of sinus area exists as actual leaf area. The leaf is mostly hairless, except for a very characteristic tuft of pale orange-brown down on the lower surface where each lobe vein joins the central vein. Overall autumn leaf coloration is generally bronze, though individual leaves may be red for a time, and is not considered particularly distinctive. The acorns, borne in a shallow, thin cap, are hemispherical, 10–16 millimeters (13⁄32–5⁄8 in) long and 9–15 mm (11⁄32–19⁄32 in) broad, green maturing pale brown about 18 months after pollination. Unless processed using traditional methods, the acorn is unpalatable because the kernel is very bitter.

In its natural environment pin oak is a relatively short-lived, fast-growing pioneer or riparian species with a lifespan of approximately 120 years against many oaks which can live several centuries. Despite this there are many examples of pin oak that exceed this lifespan. It develops a shallow, fibrous root system, unlike many oaks, which have a strong, deep taproot when young.

A characteristic shared by a few other oak species, and also some beeches and hornbeams, is the retention of leaves through the winter on juvenile trees, a natural phenomenon referred to as marcescence. Young trees under 6 m (20 ft) are often covered with leaves year-round, though the leaves die in the fall, remaining attached to the shoots until the new leaves appear in the spring. As with many other oak species, dead pin oak branches stay on the tree for many years.

Like all oaks, flowering and leaf-out occur in late spring when all frost danger has passed. The flowers are monoecious catkins which, being self-incompatible, require the presence of another oak for pollination. Any species in the red oak group can serve as a pollinator, but in pin oak’s natural range, this will usually be northern red oak or scarlet oak. Interspecies hybridization occurs freely. The acorns require two growing seasons to develop.

It is naturally a wetland tree, confined to acidic soils, and does not tolerate limestone or sandy Florida soil, and grows at low altitudes from sea level up to 350 m (1,148 ft).

It grows primarily on level or nearly level, poorly drained, alluvial floodplain and river-bottom soils with high clay content. They are usually found on sites that flood intermittently during the dormant season, but do not ordinarily flood during the growing season. They do not grow on the lowest, most poorly drained sites that may be covered with standing water through much of the growing season. However, they do grow extensively on poorly drained upland “pin oak flats” on the glacial till plains of southwestern Ohio, southern Illinois and Indiana, and northern Missouri. The level topography and presence of a claypan in the soil of these areas cause these sites to be excessively wet in winter and spring.

II. How to Grow and Care

Sunlight

Pin oak should be planted in a field with full sun. It gives shade, shady plants can be planted under it.

Temperature

Pin oak grows in a large range of temperatures. It is adaptable in hardiness zones 5-9.It prefers well drained soil with adequate ventilation in the tree canopy. Pin oak will not do well in standing water. Also, leaf molds pose serious threats if the leaves cannot dry out in the wind. So make sure they are not stuck against buildings where rainwater may drain.

Watering

Quercus palustris, colloquially known as pin oak, is a deciduous tree native to North America. Due to its favorable growing qualities and beautiful bronze coloration in autumn, pin oak is one of the most common oak species used in landscaping.

Soil

Ideal soils are well-drained loam, sandy-loam, or sandy-clay soils. Some alluvial fan areas and silts harbor good oaks stands. The key in all of these is that the soil is well-drained. Standing water cannot be tolerated by oaks.

Fertilizing

Pin oak can survive and thrive without supplemental fertilization. But if you wish to give them extra nutrients you can add some of 12-6-6 (N-P-K) fertilizer. This has more of a ratio of nitrogen than phosphorus and potassium. Also, consider the natural environment of oaks. They grow where there is lots of forest litter. This forest litter acts as natural mulch that breaks down into organic matter and humus. So one way to give some natural nutrition is to spread mulch by your oak trees. They will love the extra organic matter.

Planting Instructions

It may takes a very long time if you want to get a mature oak tree from an acorn. But with patience, planting a small tree is still fun. Be sure to kill weevil larvae by soaking the acorns in 41 ℃ water for 30 minutes, stratify in moist sand in the refrigerator (not freezer), and plant in the springtime.

Pruning

Branches should be pruned to avoid moist pockets or where heavy branches may fall on people or buildings. Avoid having branches that grow with leaves tight together or pressed against buildings. If rain collects in these pockets then molds and fungi can attack. Pin oak love having their leaves dry out in a well ventilated breeze.

To ensure that no danger occurs from the brittle hardwood branches, make sure that heavy branches do not hang over walking paths or outbuildings. Also, do not let children play near oaks in a thunderstorm as they are susceptible to falling branches and lightning strikes.

Propagation

If you wish to propagate the Oak from acorns, place the fruit in water overnight. Then plant the acorn in a potting substrate and place in a bright, warm spot. Water it regularly. The small Pin Oak will be ready for planting in the following year.

Pests and Diseases

Although native trees, Pin Oaks are not without problems. There are several key environmental factors that can harm the plant, as well as several domestic and invasive pests and diseases. Every homeowner should learn to recognize the risk factors and take mitigating action against these, as prevention is the best course of action.

Problems

Root Suffocation of Oak Trees

Once established, it is very important to not dump fill soil on top of current soil that the Oak inhabits. Roots of Oak trees like to breathe, and adding just 1″ (2.5 cm) of soil on top can cause the roots to suffocate and die, killing the tree completely. Research has shown that more compact soil results in less oxygen for roots, and more dieback for limbs.

Bark Damage

In comparison to other Oak species, the bark of Pin Oak is thin. This makes it particularly prone to damage by lawn mowers, mechanical damage, or fire.

Branches Dying

Should you notice individual branches dying on a Pin Oak tree, you should inspect the affected limb for any two-lined chestnut borers, scale insects, or canker fungus. If the limb is high up, you should consider contacting a professional tree service. With many Oak diseases and pests, quick action can be the difference between life and death of the tree.

Pin Oak leaves turning yellow / Iron Chlorosis

Should you notice Pin Oak leaves yellowing, or turning yellow, then there can be a few causes. If soil pH is high (>7.0) the Pin Oak can suffer from Iron chlorosis. This can only be corrected by lowering the pH level back to a slightly acidic level.

Alternatively, if the pH is ok, then you may consider a light top dressing of compost within the drip-line to correct any other nutrient imbalance.

Common Pests

The two-lined chestnut borer can damage Pin Oaks. Also, like may other species of Oak the Pin Oak is susceptible to defoliation by the invasive Gypsy Moth, tent caterpillars, and attack by scale insects.

You should periodically inspect your trees during the growing season for any of these pests, and if found, contact an arborist. Although some of these insects can be treated by the average DIY homeowner, it may prove beneficial long-term to use a professional considering the time invested in growing mature landscape trees.

Gypsy Moth

An invasive pest that arrived some years ago has been wreaking havoc in Oak forests throughout the Northeast and Mid-Atlantic. Gypsy Moth caterpillars can defoliate and damage many species of Oak Trees.

Homeowners should inspect trees for infestations, as well as remove possible nesting sites. Females lay eggs on piles of firewood, rock, and dead branches. Should you notice an egg mass on one of those, remove it. Also, if there is a high concentration of gypsy moths on a tree, insecticides are an option (but you will likely kill beneficial insects as well).

Galls on Oak Trees

There are two different wasps that may lay eggs on twigs of Oak Trees that result in ugly golf-ball sized galls. One is commonly referred to as horned oak gall, while the other is gouty oak-gall. These unsightly galls persist for years even after the wasp larva has exited. And if the infestation is bad enough can result in dead limbs.

There is no standard treatment for this problem. Since the larvae may take two years to exit a gall, a single pesticide application will not be effective. Furthermore, any pesticide application can result in harm to all beneficial insects that may prey on the larvae (a natural defense).

If you notice a small number of galls that can be reached with a pole saw, then you should remove them. Otherwise, if you see a large infestation, it is best to contact a professional arborist to consult with to determine the most effective remedy.

Scale

Scale is a pest that infects Pin Oaks (and several other hardwoods). There are several different types of scale that can infect Pin Oak. Scale insects are sap-suckers that rob the branches of nutrients.

Since there are many different types, it may be best to call a professional to identify the specific type of scale, and treat it. However I will provide some info of two common Scale types that effect Pin Oak trees:

Obscure Scale

The key symptom to look for is die-back of limbs and branches, and small bumps on the tree, sunken or pitted areas on the bark, giving it a roughened appearance. The bumps are approximately 1/4″ diameter and have waxy covers with a black center for “Obscure Scale”.

Obscure Scale will primarily attack younger twigs. Finding the problem early will make management much easier.

Control is difficult, as new bugs often settle in where the previous bugs lived, which provides it with some protection from pesticides. But you can spray an insecticide during summer when the Obscure scale is active.

Kermes Scale

Another form of scale is Kermes scale, which can be controlled with an oil spray in the Spring while the tree is dormant. This must be applied before the tree leaves emerge in Spring. An additional spray in the fall can further kill scales that were missed, as they migrate during the fall.

Common Diseases

Oak Wilt

A common and fatal disease can be a fungus commonly known as Oak Wilt.

Oak Wilt is a fungus spread by the Nitidulid Beetle that disrupts the water circulation system in an Oak Tree and is often fatal. Recently pruned limbs or damaged bark will attract the Beetle and infect the tree. Once infected, it is difficult to cure or stop.

Prevention is the best strategy against Oak Wilt. Only prune trees during Fall/Winter when insect activity is at a minimum. Do not prune or damage trees between February or June. Due the thin bark on Pin Oaks (previously noted) it is important to be careful with lawn mowers and trimmers, as any puncture wounds can lead to infection via the beetle.

If you suspect you have the disease, or any nearby Oak Tree has the disease, contact a professional arborist to develop a containment plant. That is the best way to save as many Oak trees as possible.

Leaf Blister Fungus

Primarily a cosmetic disease, Leaf Blister fungus will affect young emerging leaves in the Spring. Maintaining a healthy tree is the best prevention. Even if nothing is done, it is likely that the disease will lessen throughout the growing season.

Canker Fungus

Canker Fungus is an opportunistic pathogen that can harm and infect weak or stressed trees. The primary system will be a black canker or tumor like growth on the trunk, leading the bark to pop off and showing a fungal mat underneath.

Once the black canker is visible, it is often fatal for the tree. Healthy Oak trees are able to fight off any infection. Once infection takes hold, it is likely fatal.

III. Uses and Benefits 

In its native range, pin oak is the most commonly used landscaping oak along with northern red oak due to its ease of transplant, relatively fast growth, and pollution tolerance. However, as it is naturally adapted to moist, acidic soils, it may develop a condition known as iron chlorosis on less suitable locations, causing the tree to shed leaves during the growing season and rot from the top down. Mature pin oaks are often too big to treat and this nutrient deficiency on alkaline soil may eventually kill them. The drooping lower branches can also be a problem, interfering with access for traffic and pedestrians.

It is also cultivated in parks and large gardens in the United Kingdom, and has gained the Royal Horticultural Society’s Award of Garden Merit.

The wood is generally marketed as red oak, but is of significantly inferior quality, being somewhat weaker, often with many small knots. The wood is hard and heavy and is used in general construction and for firewood. The bark was used by some Native American tribes to make a drink for treatment of intestinal pain.

Swamp Spanish Oak (Quercus palustris) Details

Common name Oaks, Pin Oak, Swamp Oak, Swamp Spanish Oak
Botanical name Quercus palustris
Plant type Native Plant
Hardiness zone 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b
Growth rate Fast
Harvest time Fall
Height 50 ft. 0 in. - 70 ft. 0 in.
Width 50 ft. 0 in. - 70 ft. 0 in.
Sunlight Full sun (6 or more hours of direct sunlight a day)
Soil condition Clay
Flower color Gold/Yellow
Leaf color Green