Root Rot in Cannabis: Signs and Fixes

Your plant is declining, drooping and yellowing, and nothing you feed seems to help. If the medium is wet, the problem may be at the roots. Root rot can look like several problems at once, so a quick root check is the way to know.

Cannie showing advanced root rot — Advanced

“I am droopy and my feet feel soggy. Can you check my roots?”

Where it shows

The whole plant, as an unexplained decline.

What it looks like

Everything droops and yellows despite the medium being wet, with no crisp damage anywhere. Growth stalls. Roots go brown and smell sour.

How to confirm it

The whole plant droops and yellows despite a wet medium.
There is no crisp damage anywhere.
Growth stalls.
Healthy roots are white and smell earthy. Rotting roots are brown, slimy and smell sour.
In hydro, roots may look brown and stringy.

Why it happens

Waterlogged medium starves the roots of oxygen and anaerobic pathogens take hold. Overwatering is the usual precursor.

Waterlogged medium starving roots of oxygen.
Overwatering, the usual starting point.
Poor drainage or no drainage holes.
Warm, low-oxygen water in hydro systems.

How to fix it

Cannie's quick fix, in order:

This looks like several deficiencies at once. If nothing you feed helps and the medium is wet, check the roots.
Healthy roots are white and smell earthy. Brown, slimy or sour-smelling roots confirm it.
Improve drainage and oxygenation; let the medium actually dry between waterings.

If nothing you feed helps and the medium is wet, check the roots.
Confirm by color and smell: brown, slimy or sour roots mean rot.
Let the medium actually dry between waterings.
Improve drainage and oxygen at the roots.
In hydro, add air stones and keep water cool.

Organic options

Beneficial microbes

Products with Bacillus or Trichoderma help protect roots. Apply to the root zone following the label.

Better drainage

Add perlite or rice hulls when transplanting to give roots air.

Fabric pots

Let the medium breathe and dry evenly.

Aeration in hydro

Air stones and cool water keep oxygen high and slow root pathogens.

Read and follow every product label. Organic friendly does not mean certified organic; check the listing if that matters to you.

Veg or flower?

Root rot can strike at any stage, but recovery is slower in flower. Catching it early in veg gives the plant time to grow new roots.

Don't confuse it with overwatered

Overwatering is the cause; root rot is what it becomes if it continues. Root rot adds yellowing, stalled growth and a sour smell at the roots. Read the overwatered page.

Prevent it next time

Water by pot weight, not schedule.
Use a well-draining mix and pots with drainage.
Do not let pots sit in standing water.
In hydro, keep the reservoir clean and well aerated.

Questions growers ask

What does root rot look like in cannabis?

The plant droops and yellows in wet soil. Roots turn brown, slimy and smell sour instead of white and earthy.

Can a plant recover from root rot?

Often, if caught early. Improve drainage, let the medium dry, and support roots with beneficial microbes.

How is root rot different from overwatering?

Overwatering is the cause, and root rot is what it becomes if it continues. Root rot adds yellowing, stalled growth and sour roots.

Where these figures come from

These points match published grow books, page by page. They are grower practice, not research: none of these books cites a study, so where science and the books differ, this page follows the science.

Waterlogged medium starves roots of oxygen; overwatering is the usual precursor. Paull and Zetta (2020), e-book p. 122 to 123. Danko (2018), e-book p. 132 to 133.

Books: Danko, Cannabis: A Beginner's Guide to Growing Marijuana (Hampton Roads, 2018); Green, The Cannabis Grow Bible (4th ed., 2001); Paull and Zetta, Foolproof Guide to Growing Cannabis (2020) and The Cannabis Grow Bible (2020).