Cedar trees, whether the towering western red cedar of the Pacific Northwest or the scrubby eastern redcedar common across the Great Plains, tend to develop wide-spreading, relatively shallow root systems that concentrate most of their mass in the top couple of feet of soil. That shallow architecture is what makes cedars both resilient colonizers of tough ground and occasional headaches for homeowners with nearby sidewalks, foundations, or sewer lines. But the specifics vary a lot depending on which “cedar” you are talking about, what kind of soil it grows in, and how much competition surrounds it.
Which Cedar Are We Talking About
The word “cedar” gets applied to a surprisingly wide range of trees. True cedars belong to the genus Cedrus and include the Atlas cedar, deodar cedar, and cedar of Lebanon, all native to the Mediterranean basin and the western Himalayas. But in North America, the trees most people call cedars are not cedars at all in the botanical sense. Western red cedar (Thuja plicata) is an arborvitae. Eastern redcedar (Juniperus virginiana) is a juniper. Northern white cedar (Thuja occidentalis) is another arborvitae. They share the common name mostly because early settlers thought their aromatic wood smelled like true cedar.
This matters for understanding roots because these species belong to different families with different growth habits. Western red cedar can reach over 60 meters tall and live for centuries in moist Pacific forests, while eastern redcedar rarely tops 15 meters and thrives in dry pastures and rocky hillsides. Their root systems reflect those different lifestyles. When homeowners search for information about cedar roots, they usually mean whatever species grows in their yard, so the practical advice below applies broadly, with species-specific notes where the research gets specific.
Typical Root Depth
Most cedars keep the bulk of their root mass in the upper 60 centimeters (roughly two feet) of soil. A study of western red cedar, western hemlock, and Douglas-fir growing together on the same sites in British Columbia found that all three species reached similar depths of root penetration. The key difference was not how deep the roots went but how they structured themselves once there: western red cedar produced a high density of thin, rope-like lateral roots and fine absorbing roots, more so than either hemlock or Douglas-fir.1Canadian Journal of Forest Research. Root System Morphology of Western Hemlock, Western Red Cedar, and Douglas-fir That dense mat of fine roots near the surface is a common pattern among cedars generally and helps explain both their efficiency at capturing rainfall and their tendency to interfere with shallow infrastructure.
True cedars (Cedrus species) show a somewhat similar pattern. Deodar cedar and Atlas cedar can push sinker roots deeper than their Thuja cousins, especially in well-drained sandy or loamy soils, but even then the vast majority of absorbing roots stay in the upper soil layers where water and nutrients are most available. If you dig around the base of a mature cedar, you will almost always hit a thick web of roots within the first spade-depth before encountering anything headed downward.
How Far Roots Spread Horizontally
The old rule of thumb that tree roots stay within the dripline (the circle under the outermost branches) is wrong for most species and especially misleading for cedars. Research across several broadleaf species found that more than half of a tree’s root system grew beyond the branch dripline, and in one species the figure was closer to three-quarters.2HortScience. Tree Root Spread in Relation to Branch Dripline and Harvestable Root Ball Conifers, including cedars, follow the same general trend. Douglas-fir, growing on the same sites as western red cedar, had larger root spread and larger-diameter roots than the cedar, but cedar compensated with a denser network of finer roots.1Canadian Journal of Forest Research. Root System Morphology of Western Hemlock, Western Red Cedar, and Douglas-fir
For a homeowner, this means a mature cedar with a canopy 10 meters across could easily have roots reaching 15 meters or more from the trunk. In open landscapes with loose soil, the reach can be even greater. The roots thin out as they travel, so the risk of damage decreases with distance, but it never drops to zero within a radius that most people would consider “safe.” A good working assumption is that significant roots extend at least one and a half times the canopy radius, and possibly two or three times in sandy or irrigated soils.
What Soil Type Means for Root Behavior
Soil is the single biggest factor shaping how deep, how wide, and how aggressively cedar roots grow. In heavy clay, roots tend to stay even shallower because oxygen availability drops quickly with depth and clay resists penetration. In sandy or loamy soil, roots push deeper and spread more evenly. Compacted soil from foot traffic, construction, or heavy equipment can dramatically limit root development: one study on oak seedlings in compacted soil found that lateral root lengths shrank by about 72 percent and main root lengths dropped by more than half compared to uncompacted controls.3iForest – Biogeosciences and Forestry. Effects of soil compaction on seedling morphology, growth, and architecture of chestnut-leaved oak (Quercus castaneifolia)
Conifers, however, appear to be more stubborn about compacted soil than those short-term results suggest. A long-term study tracking conifer root growth 20 years after soil compaction found that rooting was extensive even in plots where soil strength remained high, around 3 megapascals. There were no clear differences in fine or lateral root numbers between compacted and uncompacted plots, suggesting that conifer roots slowly push through compacted ground over time rather than being permanently stunted by it.4Forest Science. Conifer Root Proliferation after 20 Years of Soil Compaction If you have a cedar growing near a former construction zone, do not assume the compacted soil kept the roots away. Given enough years, they probably got through.
Sidewalks, Driveways, and Hardscape Damage
The shallow, spreading root habit of cedars makes them a genuine concern for nearby paved surfaces. Tree roots growing under sidewalks are a well-documented cause of cracking and lifting, creating tripping hazards and costly repairs. The mechanism is straightforward: as roots thicken over the years, they press upward against the underside of pavement. Because cedar roots concentrate near the surface, they are especially prone to this kind of conflict when planted close to walkways.
Research on methods to reduce sidewalk damage found that vertical root barriers, gravel base layers, and foam treatments all helped. Barriers and foam in particular resulted in fewer roots under the pavement and pushed those that did grow there to deeper soil layers, reducing upward pressure.5Arboriculture & Urban Forestry. Comparison of Methods to Reduce Sidewalk Damage from Tree Roots If you are planting a cedar within about five meters of a sidewalk or driveway, installing a root barrier at the time of planting is far cheaper than replacing concrete later. Retrofitting a barrier around a mature tree is possible but trickier, since you inevitably cut some roots in the process.
Foundation Risk
Homeowners often worry that cedar roots will crack their foundation. The reality is more nuanced. Tree roots rarely have the force to physically break through intact, well-built concrete. What they can do is exploit existing cracks and joints, gradually widening them. The more common route to foundation damage from trees is indirect: roots draw moisture from clay soils, causing the soil to shrink. On expansive clay, this differential drying can pull the ground away from one side of a foundation, leading to uneven settling and cracking that looks like it was caused by root pressure but was actually caused by soil movement.
Cedars are moderate water users compared to notoriously thirsty species like willows or poplars, so the drying risk is lower. Still, if you have a large cedar within a few meters of your house on expansive clay soil, it is worth monitoring the foundation for signs of movement. The risk is highest during prolonged dry spells when the tree is pulling hard on every available water source. On sandy or non-expansive soil, foundation damage from cedar roots is uncommon.
Sewer Lines and Underground Pipes
Tree root intrusion into underground sewer and stormwater pipes is a major maintenance issue for municipalities and homeowners alike. Roots are drawn to the moisture, nutrients, and oxygen that leak from pipe joints and cracks. Once a root tip finds its way inside, it proliferates rapidly, eventually blocking flow and causing backups or pipe failure.6Sustainability. Review of Root Intrusions by Street Trees and Utilising Predictive Analytics to Improve Water Utility Maintenance Strategies
Cedars are not the worst offenders for pipe intrusion (willows, poplars, and certain eucalyptus species earn that distinction), but their dense fine-root networks make them capable of exploiting small openings. Experimental work on PVC pipe penetration found that roots of some species could infiltrate cracks as narrow as 0.04 millimeters, and that pipes containing soil or a mix of soil and water were penetrated about half the time.7Arboriculture & Urban Forestry. Root Penetration of Polyvinyl Chloride (PVC) stormwater and sewer pipes Cedar’s fine, rope-like roots are built for exactly this kind of opportunistic growth. If your sewer line runs within the root zone of a mature cedar and the pipe has any age-related cracks or loose joints, periodic camera inspection is a reasonable precaution.
How Eastern Redcedar Competes Underground
Eastern redcedar (Juniperus virginiana) has become one of the most aggressive woody colonizers of grasslands across the central United States, and its root behavior helps explain why. When researchers grew eastern redcedar alongside grasses and oaks and tracked where each species drew its water, they found a clear pattern of partitioning. The grasses (smooth brome, in this case) pulled water from the upper 10 to 20 centimeters of soil, while the redcedar drew from deeper layers, around 30 to 40 centimeters. When grown alongside post oak, the same split occurred: the oak used topsoil moisture and the redcedar went deeper.8PubMed Central. Effects of post oak (Quercus stellata) and smooth brome (Bromus inermis) competition on water uptake and root partitioning of eastern redcedar (Juniperus virginiana)
This ability to shift its water uptake deeper when surface moisture is already spoken for gives eastern redcedar a competitive edge in mixed landscapes. It also means that if you have a garden bed or lawn near an eastern redcedar, the tree is not necessarily competing with your shallow-rooted plants for the same water. The competition intensifies in drought, though, when every plant reaches as deep as it can.
Mycorrhizal Fungi and Root Performance
Cedar roots do not work alone. Like most trees, they form partnerships with soil fungi called mycorrhizae. These fungi colonize the root surface (or sometimes penetrate root cells) and extend hair-thin filaments called hyphae far beyond what the root itself could reach. In exchange for sugars from the tree, the fungi deliver water and nutrients, especially phosphorus, from soil the roots could never access on their own.
A meta-analysis covering a wide range of plant species found that plants colonized by arbuscular mycorrhizal fungi grew roughly 49 percent more than uncolonized plants under drought conditions, with the benefit driven partly by changes in root structure and partly by improved phosphorus uptake.9PubMed Central. Arbuscular Mycorrhizal Fungi Mediated Enhanced Biomass, Root Morphological Traits and Nutrient Uptake under Drought Stress: A Meta-Analysis While that figure comes from studies across many plant types, the underlying mechanism applies to cedars. Experimental work on tree seedlings has confirmed that mycorrhizal inoculation significantly enhances root vigor, overall growth, and biomass accumulation under water stress.10PubMed Central. Arbuscular mycorrhizal fungi improve drought toleration in Cinnamomum migao H.W.Li seedlings by increasing plant growth, nutrient uptake and biomass accumulation
For homeowners, the practical takeaway is that healthy soil biology amplifies root growth. If you are trying to limit a cedar’s root expansion (for instance, to protect a nearby structure), heavily disturbed or chemically treated soil will slow fungal colonization, but the trade-off is a less healthy tree overall. Conversely, if you want a cedar to establish quickly on a tough site, preserving existing soil fungi during planting gives it a significant head start.
Tree Stability and What Happens When You Cut Roots
Because cedar root systems are shallow, their stability depends heavily on the breadth of the root plate rather than a deep taproot acting as an anchor. Modeling of tree overturning has shown that in clay-like soils, the longest lateral roots define the size of the root-soil plate that resists toppling. In sandier soils, deeper roots and any existing taproot play a bigger role in overturning resistance, and losing even individual root elements alters the shape of the root plate and shifts the tree’s axis of rotation.11PubMed Central. Understanding the Impact of Root Morphology on Overturning Mechanisms: A Modelling Approach
This has direct consequences for construction near cedars. Trenching, which is common for utility installation, severs roots on one side of the tree in a clean line. A study on red maples subjected to simulated trenching found that cutting at one or three trunk diameters from the base caused the greatest loss in bending stress resistance, and that root volume loss correlated strongly with reduced stability.12Arboriculture & Urban Forestry. Impact of Trenching on Root Loss and Tree Stability Cedars, with their already-shallow root systems, are vulnerable to the same effect. If you must trench near a cedar, staying at least five trunk diameters away preserves the majority of root volume and keeps the tree’s wind resistance largely intact. Closer than three diameters, and you should consult an arborist about the tree’s long-term safety.
Roots as Pollution Sponges
An aspect of cedar roots that rarely comes up in homeowner discussions but matters for urban and environmental planning is their capacity to absorb pollutants from soil. Fine roots are effective at binding heavy metals in their cell walls, and the mycorrhizal fungi associated with those roots can sequester metals in their own cellular structures as well. A study of trees in Mexico City parks found that fine roots accumulated cadmium and other metals at concentrations exceeding normal plant requirements, confirming that roots act as both filters and sinks for soil contamination.13iForest – Biogeosciences and Forestry. Temporal analysis of pollutant metals in trees of three parks in Mexico City’s Metropolitan Area
Cedar species planted along roadsides or in urban parks may quietly be performing a cleanup service, trapping lead, cadmium, and zinc that would otherwise leach into groundwater. The flip side is that if you remove a mature cedar from contaminated ground, the metals stored in its roots re-enter the soil as the wood decays, unless the root material is also removed.
Roots as a Record of Erosion
Researchers in geomorphology have found an unexpected use for tree roots: reading the history of soil erosion at a site. When soil erodes away from around a root, the root tissue undergoes visible anatomical changes in the growth ring laid down that year. By analyzing exposed cedar roots that still touch the soil surface, scientists can pinpoint the year erosion first uncovered them and calculate how much soil was lost over time.14Geomorphology. Tree roots — Methodological review and new development in dating and quantifying erosive processes This technique has been used to reconstruct erosion rates on hillsides, riverbanks, and coastal bluffs where no other long-term records exist. If you notice the roots of an old cedar becoming more visible at the surface over the years, you are watching erosion in real time, and the tree itself is keeping a record of exactly when it started.