Many trees on this planet have been growing since before you or I were born. And many of them will still be standing when we’re no longer here to admire them.
Because the average tree is so large and long-living, it’s easy to forget that these plants go through various growth stages just like any other.
In this article, I’ll walk you through the stages of tree growth — from seed germination to inevitable death — and, hopefully, give you an even greater appreciation for everything these plants have to offer.
What Is A Tree?
This might seem like a silly question. But, if I asked you right now, could you really explain the difference between a tree and any other type of plant?
Admittedly, no definition is 100% agreed upon. Different organizations have slightly different criteria for what is and is not a tree. With that said, nearly everyone can agree that a tree has the following:
- A perennial (multi-year) life cycle
- A central trunk
- Rigid structural tissues, also known as wood
- An optimal mature height of at least 15 feet
Conditions For Growing Different Trees
Scientists currently estimate that there are almost 80,000 tree species growing throughout the world. So, needless to say, there’s a lot of variation in how individual trees grow and their environmental needs.
Perhaps the biggest difference between trees and other types of plant life is how long they live on average. Most species live for many decades. Some can easily live for 100 years or longer.
Most trees grow to at least 15 tall at maturity. Depending on the species, the canopy may be rounded, conical, or broad. It’s not uncommon for a tree’s branches to be as wide as (or even wider than) it is tall.
It’s a common misconception that a tree’s root system is a mirror image of the canopy above. In most cases, the roots actually extend significantly further than any of the branches.
Because of the longevity and sheer size of the average tree, site selection is often the most important part of planting. Not only do you need the right soil composition and adequate drainage for a given tree species but you also need to ensure there’s enough space for future growth.
Most trees only require supplemental water and fertilizer when they are first planted. Established trees — assuming you’ve selected a good species for your climate — survive just fine off of the native soil and precipitation.
You can grow some types of trees in containers. In many cases, however, these trees end up stunted and don’t live as long as their in-ground counterparts. This is because even a large container will restrict growth at some point.
Stages Of Tree Growth
Trees are incredibly diverse. As a result, it’s often easier to divide them up by shared characteristics than to discuss all trees as a whole.
One of the most common ways to categorize trees is by their foliage and reproductive cycles:
- Broadleaf trees have flat leaves and reproduce via seed-containing fruit. Some examples of broadleaf species include maple trees, apple trees, and birch trees.
- Conifers are trees with needle or scale-like leaves that reproduce via cones or ‘false fruit’ called arils. Common examples of conifers include pine trees, yew trees, and juniper trees.
Another useful way to differentiate trees is by their annual life cycles:
- Deciduous trees naturally shed their leaves during part of the year. In most species, this foliar loss occurs in the fall when daylight hours shorten.
- Evergreen trees are those that retain their foliage year-round. While most people think of pine trees and other conifers as evergreens, there are also many tropical, broadleaf trees that keep their leaves all year.
Regardless of type, most trees take up to 10 to 40 years to reach maturity. Trees cultivated for their flowers and/or fruit typically don’t start producing for several years after planting.
1. Seed Germination
Tree seeds come in many shapes and sizes. Some are encased within hard, protective nuts while others have ‘wings’ that help them travel via the wind. There are also many tree species whose seeds develop within edible fruit or spiny cones.
Once one of these seeds is planted, a certain amount of warmth and moisture is required to trigger germination. These conditions often need to persist for several weeks or months before the seed will ‘wake up.’
Each viable seed contains an embryo. During germination, the embryo will develop into several key parts, including the radicle, hypocotyl, and cotyledons.
The radicle, or primary root, is the first embryonic structure to break through the seed coat. It grows further down into the soil and eventually turns into the tree’s main taproot.
The seed’s hypocotyl, or primary stem, and cotyledons follow shortly behind the radicle. Cotyledons are primitive leaves that provide energy while the seed sprouts and produces its first ‘true’ leaves.
A seed is usually considered a seedling when the hypocotyl and cotyledons emerge from the soil. The length of time this takes from first planting the seed completely depends on the tree species.
Broadleaf trees are dicots, meaning each seed has two cotyledons. Conifer seedlings can have almost any number of cotyledons, which emerge from the hypocotyl in a tight whorl.
(Palm trees are monocots, so each seed has only one cotyledon. Botanically speaking, however, palm trees are not really trees.)
Cotyledons are very simple in appearance and usually don’t resemble the adult foliage of a given tree. Rest assured, all leaves that grow after the cotyledons will be true to the tree species.
When a tree seedling first sprouts, the stem is green and soft. Over time, though, it will begin to develop a woody texture. A very thin layer of bark will also form on the trunk and limbs but won’t have the same durability as a mature tree.
Young trees are generally considered seedlings until they reach a height of about 3 feet. At that point, they become saplings.
A tree will continue to be a sapling until its trunk exceeds 4 inches in diameter (measured 4.5 feet above the ground) and/or the tree reaches 15 feet tall.
The sapling stage often begins 6 months to 3 years after germination, depending on the species. Slow-growing trees can easily remain in this stage for 10 or more years.
The vast majority of nursery trees are saplings. The sapling stage is marked by rapid growth and development, so newly planted trees of this size are able to quickly recover and establish themselves.
Saplings aren’t sexually mature, so they can’t yet reproduce. As a result, it’s very rare for a sapling to flower or goes to fruit.
After leaving the sapling stage, a tree is more or less mature. But it will continue putting on new growth — in both height and width — for the rest of its life.
Depending on the species, this stage can last for many decades (or even centuries) as long as the tree remains healthy.
According to Texas A&M University, this is when a tree’s wood is of the highest quality. Most trees harvested for lumber products are felled during the mature stage.
5. Flowering & Seed Production
In terms of biology, the most important part of a tree’s life cycle is sexual maturity. Once a tree reaches this stage, it can reproduce and distribute its genetics far and wide.
Every single tree species reproduces via flowers. But surprisingly few trees produce flowers that are visually significant. For example, I’m willing to bet you’ve never noticed a pine tree flowering!
According to the University of Georgia, trees and their flowers fall into one of four sexual categories:
- Cosexual — ‘Perfect’ flowers containing both functional male and female parts on a single tree.
- Monoecious — Separate male AND female flowers on a single tree.
- Dioecious — Separate male OR female flowers on a single tree (i.e., each tree is exclusively male or female).
- Polygamous — Combination of both sexual and monoecious flowers on a single tree.
Trees need their flowers to be pollinated in order to produce viable seeds and offspring. Birds, insects, and the wind are responsible for nearly all cross-pollination between trees.
Whether or not a tree is self-fertile, or can reproduce using its own pollen, depends on the species and variety. Some trees must have pollen from a second tree to produce seeds.
6. Elderly Decline
While many tree species can live much longer than us humans, no tree is immortal. If a tree does not fall victim to an illness or physical damage during its prime, it will eventually become elderly and start to decline.
During this stage, the tree’s growth slows and it becomes less able to fight off disease or recover from environmental stressors.
It’s common to remove landscape trees at this point as they have the potential to fall and damage property or cause injury. In nature, however, many trees end up dying where they stand.
A dead, standing tree is often referred to as a snag. Although the tree itself is no longer living, this is still a crucial part of the plant’s life cycle.
Snags provide vital habitats for all kinds of wildlife. It also provides a food source for insects and fungi.
With time, the snag will fall and decay, reintroducing organic material to the soil below.
FAQ Tree Growth Stages
- Texas A&M University Harvesting lumber during the tree life cycle
- The University of Georgia Flower types of trees
Ben's horticultural interest grew when graduating from Hertfordshire University in 1997. Having contributed to numerous publications including Better Homes & Gardens, Garden Design Magazine, and The English Garden. He is also the author of Propagating Houseplants Made Easy.