What root rot is and why it happens
Root rot is a general name for diseases that decay a tree’s roots. Several different organisms can be responsible, but the usual trigger is soil that stays wet for too long. Roots need oxygen, and waterlogged or compacted soil starves them. Weakened roots are then easier for water mold organisms (such as Phytophthora) and fungi (such as Armillaria) to attack.
Common conditions behind root rot include:
- Poorly drained or heavy clay soil
- Overwatering or irrigation that soaks the trunk base
- Soil or mulch piled against the trunk, burying the root flare
- Compacted soil from construction or traffic
- Planting too deep
- Stress from drought, injury or other disease, which can make a tree more vulnerable
Signs of root rot in a tree
Root rot is hard to catch early because the damage is underground. The symptoms above ground are often general and can look like other problems.
Above-ground symptoms
- Thinning canopy, smaller leaves, or leaves that yellow or wilt even though the soil is moist
- Dieback of branch tips, or one side of the tree declining first
- Early autumn color or leaf drop
- Slow or stunted growth
- Bleeding or dark oozing at the base of the trunk, which is associated with some Phytophthora diseases
- Mushrooms or fungal growths around the base, which can point to decay fungi, though they do not always indicate a serious problem
Checking the roots and root flare
If it is safe to do so, gently clear soil and mulch from the base of the trunk to look at the root flare, the point where the trunk widens into the roots. Warning signs include soft, dark or mushy roots, a sour or musty smell, bark that peels away easily from roots, and white fungal growth between bark and wood. Healthy roots are usually firm, with a lighter color inside. Digging near the roots can injure them, so a light touch matters, and an arborist can do this assessment properly.
Common types of root rot
- Armillaria root rot (sometimes called oak root fungus or honey fungus): a fungus that can attack many woody plants. It may form honey-colored mushrooms near the base and white fungal sheets under the bark.
- Phytophthora root rot: caused by water mold organisms, favored by wet soil. It affects a wide range of trees and shrubs.
- Texas (cotton) root rot: caused by Phymatotrichopsis omnivora, found in alkaline soils of the southwestern US and northern Mexico.
- Other decay fungi: some fungi rot roots and the base of the trunk of older trees, sometimes forming brackets.
Identifying the exact cause normally needs a lab test or an arborist, and the right response differs between types.
Can a tree recover from root rot?
Sometimes, but it depends on how much of the root system is damaged, which organism is involved, and how quickly the growing conditions are corrected. A tree caught early, where the problem is mostly wet soil, has a better chance than a tree with extensive decay at the base. Once a large share of the roots has rotted, recovery is unlikely, and the tree may become structurally unsafe. Armillaria in particular can be difficult to eliminate once established.
Recovery, when it happens, is usually slow. Expect to watch the canopy over one or more growing seasons rather than seeing a quick turnaround.
How to treat root rot step by step
- Stop the extra water. Reduce or reroute irrigation, and make sure downspouts and runoff are not pooling near the trunk.
- Improve drainage. Options include regrading to move water away, breaking up compacted soil carefully, or adding drainage channels. Large trees have wide shallow roots, so avoid heavy digging.
- Uncover the root flare. Pull back excess soil and mulch from the trunk so the base can dry out. Keep mulch in a thin layer a few inches away from the bark.
- Remove dead or mushy roots only when appropriate. On small or newly planted trees, an arborist may cut away decayed roots with clean tools. On large trees this is rarely practical.
- Avoid adding stress. Hold off on heavy pruning, and avoid high-nitrogen fertilizer on a declining tree unless a soil test shows a need.
- Monitor. Note canopy density, leaf size and new growth in photos taken from the same spot each season.
Do fungicides or home remedies like baking soda work?
Fungicides are sometimes used, mainly against Phytophthora-type problems, and usually as a supplement to fixing moisture rather than a replacement. Products and effectiveness vary by organism, and they are generally less useful once decay is advanced. Check the label for your tree type and region, and ask a certified arborist or your local extension office before applying anything.
Baking soda is sometimes suggested online, but there is little evidence it treats root rot in trees. It does not fix drainage or kill the organisms deep in the root zone, and heavy applications could add salts to the soil. Correcting water and soil conditions is the more reliable approach.
When to call an arborist or consider removal
Call a certified arborist if:
- The tree is large, or close to a house, driveway or power line
- You see fungal fruiting bodies or decay at the base of the trunk
- The tree leans, has new soil heaving, or the canopy is declining quickly
- You are unsure whether the cause is root rot, drought, or something else
Roots decayed by rot can no longer anchor a tree well, so a declining tree with root problems can fall in wind or storms. See how far a tree can lean for warning signs. If an arborist finds extensive decay, removal may be the safest choice. Trunk cavities and decay at the base are covered in more detail in our guide to large holes in a tree trunk.
How long do tree roots take to rot away?
There is no single answer. After a tree dies or is cut, roots can take anywhere from a few years to well over a decade to break down, depending on species, root size, soil moisture, temperature and the fungi and insects present. Large roots of dense hardwoods tend to last longer than small roots of softer species. Decaying stumps and roots can also attract wood-feeding insects, as described in our article on termites in a tree.
Preventing root rot
- Choose species suited to your soil, and avoid planting water-sensitive trees in low or soggy spots (see trees for waterlogged and wet soil)
- Plant at the right depth, with the root flare visible at the soil surface
- Water deeply but infrequently once the tree is established, and let the soil dry between waterings
- Keep mulch thin and away from the trunk
- Protect the root zone from compaction and trenching
- Look at your trees regularly, especially after very wet periods, so small changes get noticed early