Oak Tree Life Cycle: Growth Stages

Mature oak trees are a magnificent sight to behold. They stand tall and proud, their wide canopy of branches supported by a thick, strong trunk.

The Bur Oak is one of the most common oaks in America; they grow up to an impressive 110ft tall.

The oak tree life cycle begins with a seed. The seed germinates, sprouts, and becomes a sapling. Given the ideal conditions, saplings grow into strong oak trees. In time, they bear flowers, which, when fertilized become fruit, commonly known as acorns.

They drop to the ground; those that aren't consumed by animals or ravaged by the weather contain seeds that root into the soil.

Oak Tree Life Cycle

The life cycle of an oak tree varies between varieties; however, they all share the same stages; it is the timings that differ.

Seeds

acorns

The embryo of the oak is packaged safely within a cupule – an acorn to you and me.

They grow in clusters on all types of an oak tree and drop to the ground when they're ripe, during September or October.

Rodents, deer, and birds eat the majority of fallen acorns. It is commonplace to see squirrels storing acorns for use later in the year. They don't all get dispersed; they are mostly too heavy to catch on the wind, although some might drift in free-flowing water.

The hardiest survivors that stay within 30m of the parent tree are the ones that have the best chances of taking root and germinating. The luckiest acorns land beneath the protective covering of a fallen log, in tilled soil, or safely hidden beneath a litter of leaves.

Germination

Those acorns that escape the threat; anchor themselves into the soil with an embryonic root. It grows deep in the search for water and creates an anchor for the seedling.

Whatever the climate throws at it, the strongest root will stand firm, even in icy, windy, or humid conditions.

Sprouting

acorn germinating and sprouting

Inside the embryo are two cotyledons; it is within these structures that food is stored.

During the following spring, the soil's moisture encourages the cotyledons to swell enough to crack the outer shell of the acorn.

A slender shoot slowly forms and breaks through the ground.

Seedling

seedling

The cotyledons remain a fixture of the seedling as it grows in height and girth.

They continue to feed the tiny tree for months, even as the leaves begin to form and photosynthesis begins.

It is when the chlorophyll and sunlight combine in sufficient quantities that the cotyledons fall away.

The seedling grows slowly, approximately 30-45cm per year. When it reaches 1m tall and has a diameter of around 3”, it becomes a sapling. Saplings are intolerant of competition, so this is the stage when many lose their battle to more invasive plants.

Trees that survive beyond this point and achieve a 12” diameter are known as poles and have the greatest chance of becoming a mighty oak.

Tree

The speed at which your oak tree grows is dependent on four factors:

  1. Species
  2. Soil nutrients
  3. Water
  4. Climate

There are about 600 species of oak; more than half of them are native to North and Mid America.

Species

Most of the popular species fall into the Red or White oak categories.

Red Oak

The faster-growing oak tree; it takes just 9-11 years to reach 13 – 20ft tall with a 25-30ft width.

Full maturity occurs at 30 – 35years when the tree stands 60 – 80ft high and measures 60 – 70ft wide.

White Oak

These species of oak tend to grow slowly, between 1 and 2ft annually. Therefore, white oak trees don't reach full maturity until 30 – 40 years.

At 10 – 12 years old, they stand 10 -15ft tall and 20 – 25ft wide.

Oak trees need well-drained soil with no chemical composition to grow. It should have a plentiful supply of nutrients and be as free of plant pathogens and pests as possible.

All species of oak trees have impressive canopies of 45 – 50ft wide. They create a spectacular sight, copious amounts of nesting and feeding sites for wildlife, and cast large ground shade.

Soil Nutrients

A healthy oak tree emerges from neutral pH soil with a balanced combination of nutrients.

Magnesium, calcium, potassium, nitrogen, phosphorus, and sulfur mixed result in ideal soil conditions.

Water

Oak saplings grow into healthy trees in well-drained soil. They like chemical-free soil with plenty of fresh water that doesn't linger on the surface.

Climate

Each species of oak thrive in different conditions. With such a large variety of species, there will always be one to adapt to your regional climate.

For instance, the Californian oak thrives in subtropical conditions with hot, dry summers and wet winters.

The eastern white oak exists in temperatures between 45 -70°f and with substantial snowfall.

Flowers

Oak trees might flower as young as 20 years old, although it is more commonplace for them to be around 40.

They have both male and female flowering parts. The male flowers are yellowish droplets called catkins, while the female is small reddish flowers.

The male pollen is carried on the wind until it finds the stigma at the end of a female flower. Fertilization occurs, causing the ovary to swell.

As it gets bigger, it grows a hard outer shell and a scale-like cap. It is the fruit of the oak tree – the acorn.

Oak Trees with Fruit

Oaks have to wait until maturity until they begin producing acorns; Red oaks such as the pin can start as early as 20 years while the bur oak, white, will have to wait until it is at least 35 years old.

As the years roll by, the number of acorns produced significantly increases. Throughout the lifetime of an oak tree might spawn 10,000 acorns; on average, only 1:1000 become a tree. Each fully-mature oak usually parents one other tree each year.

Old oak trees gradually reduce the number of acorns they produce until they stop growing them altogether.

Acorns grow in clusters at the outer tips of oak branches. They form from fertilized flowers and have a tough outer shell with a hard protective cap. They turn green as they ripen, changing to brown when ready to drop from the tree.

Fruit

Acorns fall from a mature oak when they are ripe, and almost all of them are consumed by squirrels, deer, and blue jays. Those that find the perfect hiding place to take root might remain there until the next spring, possibly the one after that. They bide their time until the conditions are optimal for them to grow a shoot.

Although millions of acorns fall each year, the majority don't get past the seedling stage.

Man and their machinery are almost as big a threat as their position in the food chain.

They also require lots of sunlight and air to thrive. Plants such as buckthorn and ivy crowd them out and block their path towards the sun.

Acorns lie in situ for seasons. Often hidden beneath leaves and thatch, anchored by their embryonic root, waiting for the time to sprout.

Seeds

And so we return to the beginning of the oak tree life cycle, ready to disperse its seeds and grow new life.

Final Thoughts

"From tiny acorns, great oaks grow," so the saying goes.

It isn't always so; they face many battles and hardships along the way.

From being eaten by wildlife, harmed by humans and their machinery, to fire and harsh weather conditions, the tiny acorn has to put up a fight to thrive.

But the rewards are magnificent. Each oak tree provides food and shelter to birds and wildlife, supplies shade and beauty for many decades.

Annette Marsh
For the past twenty years, Annette has allocated much of her free time towards gardening and landscaping related tasks; Planting flowers and trees, weeding, pruning, mulching, mowing, constructing ponds and various other structures, as well as growing and maintaining a vegetable garden.

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