Arborvitae are shallow-rooted trees. Their roots grow mostly outward rather than down.1Ask Extension. Arborvitae roots are killing my vegetable garden So the real question for most yards isn’t how deep the roots dig but how far they spread and what they compete with.
How Deep Arborvitae Roots Usually Grow
In landscape plantings, most arborvitae roots occupy roughly the top 10 inches of soil.2Victory Garden Boys. Planting Arborvitae for Privacy near Homes and Other Structures In large varieties, the major roots can reach about 18 to 24 inches deep.3Ask Extension. Arborvitae roots are killing my vegetable garden A compact globe type will root less deeply than a tall hedge type. In practice, a shovel or tiller working the top foot near the tree will meet most of its roots.
Height says little about root depth in arborvitae: a 20-foot hedge can still have most of its roots in the top foot. These trees anchor themselves through width rather than a deep central root.
Dig near an established tree and you’ll find many thin, fibrous roots just under the mulch or grass, plus a few thicker, rope-like roots running sideways from the trunk. Below about two feet there is very little. Cutting a few small surface roots is usually tolerated, but cutting thick roots near the trunk is not.
Young American arborvitae seedlings can start with a long single taproot.4USDA Forest Service. Silvics of North America, Volume 1: Conifers After the seedling stage, though, the tree generally develops a shallow, wide-spreading root system.5USDA Forest Service. Silvics of North America, Volume 1: Conifers In the wild, the species grows on rocky cliffs, pulling water and nutrients from cracks in the rock.6Silvics of North America. Thuja occidentalis
The depth numbers are typical ranges, not guarantees, because soil and variety both shift where roots end up. Roots at the surface are normal for this tree and don’t mean something is wrong.
How Far the Roots Spread Sideways
Arborvitae roots may spread out to the drip line, the outer edge of the branches.7Ask Extension. Arborvitae roots are killing my vegetable garden In conifers, most fine and coarse roots tend to be concentrated near the trunk,8SpringerLink / Trees. Distributions of fine and coarse tree roots in a semi-arid mountain region and their relationships with soil properties so the zone a few feet around the trunk holds the bulk of the feeding roots. A Green Giant typically grows 6 to 8 feet wide after 10 to 15 years,9WascoNursery.com. Green Giant Arborvitae Spacing: 3 Steps to Perfect Privacy which puts its roots 3 to 4 feet or more out from the trunk on each side.
To estimate your own tree’s root zone, look at the widest branches and picture a circle on the ground beneath them. Assume active roots fill that circle and may extend a little past it. The circle grows as the tree widens each year. Use it to decide where not to dig, trench, or pile soil.
In American arborvitae, roots of neighbouring trees fairly often graft together naturally.10USDA Forest Service. Silvics of North America, Volume 1: Conifers In a row, the root zones overlap into one continuous band, so removing a single hedge plant often means cutting shared roots.
Damage to roots rarely shows right away, because the branches live off stored energy for a season or more. Browning, thinning, or dieback in later years can trace back to digging, soil piled over the roots, or paving done earlier.
What Changes Root Depth in Your Soil
As soil holds more water, young arborvitae roots shift from a long taproot to shorter, thicker roots with many side branches.11USDA Forest Service. Silvics of North America, Volume 1: Conifers Seedlings from upland stock grew deep roots in well-drained soil and shallow roots in waterlogged soil.12USDA Forest Service. Silvics of North America, Volume 1: Conifers Seedlings from wetland stock showed little change between soils.13USDA Forest Service. Silvics of North America, Volume 1: Conifers Heavy, soggy clay therefore tends to keep roots shallower. Roots also grow especially readily into rotting wood.14Silvics of North America. Thuja occidentalis
You can read your own site fairly well. Low spots that stay wet after rain push roots toward the surface. Sandy or gravelly ground drains fast and encourages somewhat deeper roots. Compacted soil near new construction blocks downward growth.
Shallow roots in wet soil can be a problem. They dry out quickly during summer dry spells, and they give less grip in strong wind on soaked ground. Improving drainage before planting gives roots more usable depth.
To test drainage, dig a hole about a foot deep, fill it with water, and let it drain. Fill it again and see how long the second filling takes. If water is still standing in the hole after a day, the site is poorly drained and roots will stay shallow there. Do this in the exact spot you plan to plant, since drainage can differ across a single yard.
Will Arborvitae Roots Damage Foundations or Fences
Arborvitae roots are generally small, and damage to foundations is unlikely.15Victory Garden Boys. Planting Arborvitae for Privacy near Homes and Other Structures Most roots stay in the top foot of soil, above typical foundation footings. Roots can still enter a pipe that is already cracked and leaking, as many tree roots do.
Patios and walkways are similar. Small roots rarely lift slabs the way large-rooted trees can. Shallow irrigation lines in the root zone may be crowded or tangled, so dig carefully and by hand when repairing lines near the hedge.
Branch spread is the bigger concern near walls. Branches grow outward every year, so a tree planted close to a wall eventually presses against it. The gap you leave at planting decides whether the tree stays clear later, and distance is hard to fix afterward because moving a large arborvitae is a big job.
Planted too close to a house, the branches rub siding, and the side facing the wall gets little light and browns out. Pruning and painting become difficult. Dense foliage touching a wall keeps the surface from drying after rain, which can help mold and algae grow on siding.
How Close to Plant Arborvitae
Plant Green Giant trunks at least 6 to 8 feet from a fence, house or property line.16WascoNursery.com. Green Giant Arborvitae Spacing: 3 Steps to Perfect Privacy Their branches reach 3 to 4 feet out on each side of the trunk,17WascoNursery.com. Green Giant Arborvitae Spacing: 3 Steps to Perfect Privacy so that distance leaves 3 to 4 feet of open space between branches and the fence.18WascoNursery.com. Green Giant Arborvitae Spacing: 3 Steps to Perfect Privacy In a staggered double row, measure from the row closest to the line.19WascoNursery.com. Green Giant Arborvitae Spacing: 3 Steps to Perfect Privacy
For smaller varieties, check the mature width on the plant tag, not the current size. Plant at least half the mature width from any structure, then add a foot or two for air flow and maintenance access. Compact types can sit nearer to walls than Green Giant.
Property lines bring their own issues. Branches crossing the line can trigger disputes, so leave room to trim your side without stepping onto the neighbour’s.
Measure from the center of the planned trunk, not from the edge of the pot or root ball, to the fence or wall. Mark each trunk position with a stake or flag so you can check spacing before digging. For a row, mark every position along the line first and step back to see how the hedge will look.
Arborvitae Roots in Lawns and Vegetable Gardens
Tree roots compete hardest at the surface when grass grows under the tree.20Arboriculture & Urban Forestry. The Ecology of Tree Roots and the Practical Significance Thereof Lawn herbicides can reach a tree through these fine surface roots,21Arboriculture & Urban Forestry. The Ecology of Tree Roots and the Practical Significance Thereof so weed-and-feed products spread up to the hedge may harm it. A vegetable bed within the root zone can lose water and nutrients to the arborvitae.
Signs the hedge is stealing from your garden include plants nearest the hedge wilting first in dry weather, growth that improves noticeably with distance from the hedge, and a dense mat of fine roots when you dig in the bed. Raised beds with a liner often solve the problem. Grass struggles under the hedge too, since roots take most of the water in the top layer and dense branches cut down on light.
A better choice under arborvitae is to replace grass with a 2 to 3 inch layer of mulch out to the drip line. Keep mulch a few inches off the trunk, and avoid tilling or deep digging inside the root zone.
A root barrier such as a trench can limit arborvitae root growth but not stop it.22Ask Extension. Arborvitae roots are killing my vegetable garden – Ask Extension Roots eventually grow around it, so check barriers every few years.
To install one, dig a narrow trench along the edge of the root zone, a foot or so deep, since most roots are in the top foot. Cut through any roots you find with a sharp spade rather than tearing them. Line the trench with a root barrier sheet or edging and backfill, keeping the top edge just above the soil.
Caring for Shallow Roots After Planting
Fall- and spring-planted arborvitae survived equally well, about 94 percent.23Journal of Environmental Horticulture. Seasonal Planting, Root Regeneration and Water Deficits of Austrian Pine and Arborvitae But fall-planted trees grew about 22 percent less in height their first year.24Journal of Environmental Horticulture. Seasonal Planting, Root Regeneration and Water Deficits of Austrian Pine and Arborvitae Spring planting gives a faster start if height matters. Green Giant can establish slowly at first despite its fast-growing reputation,25Kansas State University. Growth of four conifer species during establishment and the effects of recurring short-term drought on growth and photosynthetic capacity yet once rooted, it kept root growth steady through moderate and severe drought.26Kansas State University. Growth of four conifer species during establishment and the effects of recurring short-term drought on growth and photosynthetic capacity
For watering, soak the root ball and surrounding soil weekly in dry spells for the first two years. Water slowly so it sinks into the top foot instead of running off, and check the soil a few inches down before watering again. Established hedges still need water in long droughts because the roots are shallow.
In winter, frozen surface soil cuts off water to the shallow roots, while evergreen foliage keeps losing water in wind and sun. A deep watering before the ground freezes helps reduce browning.
American arborvitae relies on partnerships with soil fungi that help roots take up nutrients.27Tree Physiology. Freezing tolerance and recovery of arbuscular-mycorrhizal and non-mycorrhizal Thuja occidentalis Adding these root fungi to seedlings improved growth and phosphorus uptake as much as fertilizer did.28New Forests. Arbuscular mycorrhizal inoculation has similar benefits to fertilization for Thuja occidentalis L. seedling nutrition and growth on peat soil over a range of pH: implications for restoration
For the planting hole, dig about as deep as the root ball but two to three times as wide, since roots will spread outward. Set the tree on undisturbed soil so it does not sink, and keep the top of the root ball level with or slightly above the ground. Backfill with the soil you dug out, and water as you fill to settle out air pockets.
Slicing or teasing circling roots at planting did not clearly improve new root growth in other trees compared with leaving them alone.29Arboriculture & Urban Forestry. Mechanical Root-Disruption Practices and Their Effect on Circling Roots of Pot-Bound Tilia cordata Mill. and Salix alba L. ‘Niobe’ Gentle loosening is fine, but heavy cutting is not needed.