# Do trees share through their roots? Root grafts, water, sugar and disease

> Why roots of nearby trees grow together, how a graft can keep a leafless stump alive or carry oak wilt to the next oak, and what to do before cutting one down.

Published 2026-11-07. Tags: How trees work, Protection & care. By Blue Whale Trees, a native tree nursery in the United States. Web version: https://bluewhaletrees.com/articles/do-trees-share-through-their-roots/

Trees do share through their roots, wherever a root has fused with a neighbor's into a root graft, most often between trees of one species. A working graft passes water, sugars and minerals from tree to tree. It passes [oak wilt](https://bluewhaletrees.com/articles/glossary/index.html.md#oak-wilt), Dutch elm disease and herbicide painted on a stump as well. Grafts have been reported in 150 to more than 200 kinds of trees, and in some stands more than 60 percent of the trees are joined. Claims that fungal networks let whole forests feed and warn one another have little evidence behind them.

![Two smooth gray beech trunks side by side, their flared bases merging into one at the ground among fallen brown leaves](https://bluewhaletrees.com/img/articles/do-trees-share-through-their-roots-1-1000.jpg?v=5c0b41ef "Two American beech joined at the base by root grafts, on November 7, 2026. Water, sugar and disease can pass between trees joined this way.")
*Photo: Blue Whale Trees*

## How two trees' roots grow together

Where the roots of two neighbors touch, their vascular tissues can fuse, so the wood that carries water and the inner bark that carries sugar run from tree to tree. Most grafts join one species, and among oaks the red oaks graft most with one another, though a [northern pin oak](https://bluewhaletrees.com/plants/northern-pin-oak/index.html.md) can graft to a [bur oak](https://bluewhaletrees.com/plants/bur-oak/index.html.md).

Grafts lie out of sight, so the studies that count them wash whole plots of roots free of soil. In three natural [balsam fir](https://bluewhaletrees.com/plants/balsam-fir/index.html.md) stands in Quebec, about a third of the trees were grafted. Forming a graft has a cost: [jack pines](https://bluewhaletrees.com/plants/jack-pine/index.html.md) grew less while their grafts formed, and more afterward.

## What passes: water and sugar

In New Zealand, Martin Bader and Sebastian Leuzinger followed a kauri stump with no leaves that its grafted neighbors kept alive. Its water fell by day, while the neighbors drew water hardest, and recovered at night. Without leaves, it must get its sugar from them, and they gain the use of its roots:

> "Intact kauri trees […] may adopt the root system of a connected tree that has lost its crown, thereby extending their rooting space and at the same time allowing trunk remnants to persist over long periods of time." (Bader and Leuzinger, *Hydraulic Coupling of a Leafless Kauri Tree Remnant to Conspecific Hosts*, 2019)

Shaded lodgepole pines grafted to a sunlit neighbor held more stored sugar in their roots than shaded pines without a graft, and large grafts carried more than small ones. A shaded tree can lean on its neighbors that way, but the sharing is not always even. Under heavy crowding, the larger balsam firs of a joined group held their growth best.

![Two tuliptree trunks rising from one old stump, joined at the ground by a collar of living wood around a leaf-filled hollow](https://bluewhaletrees.com/img/articles/do-trees-share-through-their-roots-4-1000.jpg?v=716b35ba "Two tuliptrees grown from the sprouts of one stump, on October 29, 2023, still joined by living wood around the hollow where the old stump rotted. Trunks like these share one root system.")
*Photo: Blue Whale Trees*

## Disease and weed killer cross too

Oak wilt reaches new ground on beetles, but most new infections come from the fungus moving through grafted roots between nearby oaks. An oak infected that way can wilt and die soon after it leafs out the next spring. In one urban study most such spread came within 30 feet, and some oaks wilted 50 feet from the nearest infected tree.

Dutch elm disease crosses between [American elms](https://bluewhaletrees.com/plants/american-elm/index.html.md) the same way, above all among elms within 25 to 50 feet of each other. Armillaria and Ganoderma, two fungi that rot roots, can [spread to nearby trees through grafts](https://bluewhaletrees.com/articles/fungus-is-not-a-death-sentence/index.html.md) as well.

Herbicide painted on a cut stump, or on sprouts from a root, can move into any tree sharing that root system and kill it. Stump killers with picloram, dicamba or 2,4-D can also leak from treated roots into the soil, a loss called flashback. Either way, [herbicide damage](https://bluewhaletrees.com/articles/herbicide-damage-on-trees/index.html.md) can show in a tree no one treated.

## Root sprouts and fungal networks

A root sprout is another kind of link, a stem raised from a tree's own root that carries its genes. An [American beech](https://bluewhaletrees.com/plants/american-beech/index.html.md) under a threat such as [beech leaf disease](https://bluewhaletrees.com/articles/beech-leaf-disease/index.html.md) sends up a thicket of root sprouts, which catch its diseases and often die before it does.

[Sassafras](https://bluewhaletrees.com/plants/sassafras/index.html.md) and [pawpaw](https://bluewhaletrees.com/plants/pawpaw/index.html.md) spread into colonies by [root suckers](https://bluewhaletrees.com/articles/suckers-at-the-base-of-a-tree/index.html.md), and a pawpaw patch may be a single plant. In quaking aspen, which we do not grow, a whole clone rises from the root system of one seedling. Blue Whale Trees grows every tree it sells from seed, so each seedling is genetically distinct, as the young trees of a wild stand are.

![A woodland floor covered by a low thicket of young beech in pale fall leaves, tall trunks rising behind](https://bluewhaletrees.com/img/articles/do-trees-share-through-their-roots-3-1000.jpg?v=d0a61a17 "Young beech crowding a woodland floor on November 7, 2026. A diseased beech sends up root sprouts like these, and they die of its diseases, often before it does.")
*Photo: Blue Whale Trees*

Mycorrhizal fungi, [partners of the roots](https://bluewhaletrees.com/articles/mushrooms-at-the-base-of-a-tree/index.html.md) that help them take up water and nutrients, can also join the roots of several plants into a common mycorrhizal network, or CMN. Whether such networks are widespread in forests, or help seedlings, is not shown, since field results vary too widely or have other explanations. One claim fares worst in a 2023 review:

> "The claim that mature trees preferentially send resources and defence signals to offspring through CMNs has no peer-reviewed, published evidence." (Karst, Jones and Hoeksema, *Positive citation bias and overinterpreted results lead to misinformation on common mycorrhizal networks in forests*, 2023)

## Before you cut, treat or replant

Before an oak with oak wilt or an elm with Dutch elm disease comes down, have its grafts to healthy neighbors cut first. Against oak wilt, a tree care professional cuts the roots, usually with a vibratory plow and its 5-foot blade. The line runs between the first and second ring of healthy oaks, since the nearest may already carry the fungus.

Keep weed killer off any stump or root sprout that may share roots with a tree you want to keep. Where oak wilt or Dutch elm disease killed a tree, the table of [what each disease leaves behind](https://bluewhaletrees.com/articles/planting-where-a-tree-was-removed/index.html.md#when-the-old-tree-died-of-a-disease) gives what to plant in its place. The [tree finder](https://bluewhaletrees.com/tools/tree-finder/index.html.md?size=large-tree) lists the large trees for your zone, sun and soil moisture.

## Common questions

### Do trees communicate through their roots?

Trees joined by root grafts pass water, sugar and sometimes disease between them. No peer-reviewed, published study shows mother trees favoring their own young with food or warnings through fungal networks.

### Are aspen trees connected by their roots?

A quaking aspen clone rises from the root system of one seedling, so a grove can be a single plant. East of the Rockies a clone typically covers a fraction of an acre, while one in Utah covers 107 acres.

### Can a tree stump stay alive?

Yes, in two ways. A stump that sends up shoots is alive on its own roots, and one grafted to living neighbors of its species can live a long time without a leaf on their water and sugar.

### Can oak wilt spread through the roots to my other oaks?

Yes: most new oak wilt infections come through roots grafted between nearby oaks, mostly within 30 feet in one study. Cutting those roots between sick and healthy oaks is the best way to stop it.

## Sources

- [Hydraulic Coupling of a Leafless Kauri Tree Remnant to Conspecific Hosts](https://pmc.ncbi.nlm.nih.gov/articles/PMC6831820/): M.K.-F. Bader and S. Leuzinger, iScience 19 (2019): root grafts in some 150 woody species and more than 60 percent of a population grafted, a living kauri stump whose water fell by day and recovered at night opposite its neighbors, its need for sugar from them, its callused edge, and the quotation on host trees adopting its roots.
- [Does natural root grafting make trees better competitors?](https://amu.hal.science/hal-04043031/document): E. Quer, M. Helluy, V. Baldy and A. DesRochers, Oikos (2022), e09666, the authors' copy in HAL: roots that fuse by their vascular tissues where they touch, grafts in more than 200 tree species, about a third of the trees grafted in three natural balsam fir stands in Quebec, found by hydraulic excavation, and larger grafted trees holding their growth under heavy crowding.
- [Effect of natural root grafting on growth response of jack pine (Pinus banksiana; Pinaceae)](https://pubmed.ncbi.nlm.nih.gov/21653509/): E. Tarroux and A. DesRochers, American Journal of Botany 98 (2011): hydraulically excavated plots, and jack pines growing less while their grafts formed and more afterward.
- [Carbohydrate transfer through root grafts to support shaded trees](https://pubmed.ncbi.nlm.nih.gov/16651251/): E.C. Fraser, V.J. Lieffers and S.M. Landhäusser, Tree Physiology 26 (2006): shaded lodgepole pines holding more root sugar when grafted to a sunlit neighbor, larger grafts carrying more, and grafts that let shaded trees persist.
- [Positive citation bias and overinterpreted results lead to misinformation on common mycorrhizal networks in forests](https://pubmed.ncbi.nlm.nih.gov/36782032/): J. Karst, M.D. Jones and J.D. Hoeksema, Nature Ecology & Evolution 7 (2023): what a common mycorrhizal network is, the claims of widespread networks and of help to seedlings as insufficiently supported, and the quotation on mature trees and their offspring.
- [Oak wilt in Minnesota](https://extension.umn.edu/garden-and-home/yard-and-garden/yard-and-garden-problems/oak-wilt-in-minnesota): University of Minnesota Extension: beetles starting new centers and grafted roots causing most new infections, wilting soon after leaf-out the next spring, spread mostly within 30 feet and up to 50, red oaks grafting most with one another and northern pin oak with bur oak, root cutting with a vibratory plow and a 5-foot blade between the first and second ring of healthy oaks, felling after root cutting, and root cutting as the best way to stop the spread.
- [Dutch elm disease](https://mortonarb.org/plant-and-protect/tree-plant-care/plant-care-resources/dutch-elm-disease/): The Morton Arboretum: the disease passing through root grafts, grafts commonest between elms of one species, and grafts severed before a diseased elm is removed where elms grow within 25 to 50 feet of each other.
- [Cut Stump Application of Herbicides to Manage Woody Vegetation](https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1401.pdf): University of Arizona Cooperative Extension (Jeff Schalau, AZ1401, revised 2011): neighbors of one species sharing a root system, herbicide on a stump or on root sprouts moving into trees never treated, flashback from picloram, dicamba and 2,4-D, and no herbicide on sprouts from the roots of a tree to keep.
- [Beech Leaf Disease in Connecticut](https://portal.ct.gov/deep/forestry/forest-protection/beech-leaf-disease-in-connecticut): Connecticut Department of Energy and Environmental Protection, Forestry (updated August 2026): root sprouts sent up by a diseased American beech, genetically identical to it, forming a thicket around it and dying of its diseases, often before the parent.
- [Quaking Aspen](https://research.fs.usda.gov/silvics/quaking-aspen): USDA Forest Service, Silvics of North America: a clone formed from the root system of one seedling, clones of a fraction of an acre east of the Rockies and one of 107 acres in Utah, and neighboring clones differing in leaf-out time and autumn color.

## Related

- Next step: [Open the tree finder](https://bluewhaletrees.com/tools/tree-finder/index.html.md?size=large-tree)
- [Planting a new tree where one was removed or a stump was ground](https://bluewhaletrees.com/articles/planting-where-a-tree-was-removed/index.html.md)
- [Suckers at the base of a tree: why natives sucker, and which to keep](https://bluewhaletrees.com/articles/suckers-at-the-base-of-a-tree/index.html.md)
- [Herbicide damage on trees: cupped leaves, weed-and-feed, drift from a neighbor’s lawn, and recovery](https://bluewhaletrees.com/articles/herbicide-damage-on-trees/index.html.md)
- [Mushrooms at the base of a tree: the few that mean root rot, and the many that do not](https://bluewhaletrees.com/articles/mushrooms-at-the-base-of-a-tree/index.html.md)