How Big Is An Arborvitae Root System

An arborvitae root system can be surprisingly wide but shallow for a tree of its size.
 
This is because arborvitae roots stay in the top several inches of soil rather than growing deep.
 
If you’re planting arborvitae on your property, knowing how big an arborvitae root system gets helps you choose the right spot.
 
The root system of arborvitae is not like a deep taproot that anchors a large tree.
 
Instead, the roots spread outward horizontally to support the tree above ground.
 
In this post we’ll talk about typical dimensions, why the roots stay shallow, and what that means for your yard.
 
Let’s dig in.
 

How Big Is an Arborvitae Root System?

The typical arborvitae root system extends as wide as the tree is tall or sometimes even wider.
 
For a mature arborvitae that is 10 feet tall, its root system can spread 8 to 12 feet in diameter.
 
This means the outward reach of an arborvitae root system is roughly equal to the height of the tree.
 
The root system of arborvitae is mostly fibrous and grows close to the soil surface.
 
Most of the feeder roots are found in the top 12 to 18 inches of soil.
 
The depth of an arborvitae root system rarely goes below 2 feet in most soil types.
 

1. Height to Root Spread Ratio

One reliable way to estimate how big an arborvitae root system is uses the tree’s height.
 
For every foot of height, expect the root spread to be about 1 to 1.5 feet outward.
 
A 15‑foot arborvitae therefore has a root system that spans 15 to 22 feet across.
 
This ratio works well for healthy, established trees in decent soil.
 

2. Shallow Depth of Arborvitae Roots

The depth of an arborvitae root system rarely exceeds 18 inches in normal garden soil.
 
Most feeder roots are concentrated in the top 8 to 12 inches where oxygen and moisture are abundant.
 
The root system of arborvitae does not develop a strong taproot.
 
Instead, the roots grow mostly laterally, anchoring the tree by weight and friction rather than by deep penetration.
 

Why Arborvitae Root Systems Stay Shallow

Understanding why an arborvitae root system stays shallow helps you plan for its growth.
 
These trees are adapted to moist, well‑drained soils found in lowlands and along streams.
 
In such environments, shallow roots efficiently capture water and nutrients from the surface.
 
The root system of arborvitae also benefits from the fact that these trees are evergreen and grow slowly.
 
There is less need for a deep root to support a massive canopy like in some deciduous trees.
 

1. Adaptation to Wet Soils

Arborvitae naturally grow in areas where the water table is high.
 
A deep taproot would be unnecessary and could even rot in saturated soil.
 
The shallow arborvitae root system spreads out to capture oxygen from the upper soil layers.
 

2. Low Nutrient Demand

The root system of arborvitae is efficient because the tree doesn’t produce a huge leaf mass each year.
 
Evergreen leaves are long‑lived, so the roots don’t need to push deep to find new nutrients constantly.
 
This efficiency allows the arborvitae root system to thrive in a relatively small volume of soil.
 

Factors That Affect Arborvitae Root System Size

How big an arborvitae root system actually gets depends on several factors.
 
The root system of arborvitae can vary by species, soil type, and how the tree is maintained.
 

1. Soil Type and Compaction

In loose, loamy soil, arborvitae roots can spread farther and penetrate a little deeper.
 
Compact clay or rocky soil restricts the arborvitae root system to a smaller area.
 
If your soil is dense, the root system of arborvitae will be more confined and shallower.
 

2. Irrigation and Watering Habits

Frequent shallow watering encourages roots to stay near the surface.
 
Deep, infrequent watering encourages the arborvitae root system to grow slightly deeper.
 
However, even with deep watering, the root system of arborvitae rarely exceeds 24 inches depth.
 

3. Arborvitae Variety or Cultivar

Larger arborvitae like ‘Green Giant’ develop a bigger root system than dwarf varieties.
 
A dwarf arborvitae root system might span only 2 to 3 feet wide.
 
The overall size of the arborvitae root system generally matches the above‑ground spread.
 

Managing Arborvitae Root Systems Near Structures

Knowing how big an arborvitae root system is helps you avoid problems with foundations, sidewalks, and driveways.
 
Because the arborvitae root system is shallow and fibrous, it rarely causes serious damage to building foundations.
 
But it can still lift pavers or interfere with underground sprinklers if planted too close.
 

1. Safe Planting Distance

Plant arborvitae at least half the mature width away from any hard surface.
 
For a 10‑foot tree with a 10‑foot root spread, give at least 5 feet of clearance.
 
The root system of arborvitae won’t crack concrete, but it may bulge soft surfaces like asphalt.
 

2. Protecting Nearby Plants

The shallow arborvitae root system competes for surface water and nutrients.
 
Keep perennials and grass at least a few feet away from the base of the tree.
 
Mulching helps reduce competition and keeps the root system of arborvitae cool and moist.
 

So, How Big Is an Arborvitae Root System?

An arborvitae root system is wide but shallow, typically spreading as far as the tree is tall but staying in the top 18 inches of soil.
 
For a mature 10‑foot arborvitae, the root system of arborvitae measures about 8 to 12 feet across and only 12 to 18 inches deep.
 
The exact size of an arborvitae root system varies with soil, variety, and care, but the shallow‑spread pattern remains constant.
 
Now you know how big an arborvitae root system really is, so you can plant confidently without surprises.
 
Happy planting.