A Fungus Among Us

Root, Stem and Leaf Rot

Concerned ? If you have houseplants you should be ! Root rot is one of the top reasons why people call me for help with their Indoor plants.  They send me pictures of their plants in dire straits and looking stressed.

Pictures like these:

rotted roots up to the stem !

 

not likely its going to recover :(

Their cause for alarm is real - the plant is in need of immediate attention.  Unfortunately, many times it is too late in the process. The culprit is a fungus !  

Where does it come from?

A large number of soil-borne fungi cause root rots. Pythium, Phytophthora, Erwinia, Rhizoctonia, and Fusarium species are the most common rot fungi. The are many many more species that also cause rot. These fungi affect a wide range of plants, but all have one characteristic in common -  all prefer wet soil conditions.  

fungal by products (darker tissues) block the water carrying vessels

Fusarium will travel up the stem and blocks all the water vessels.  Oddly enough it causes the foliage at top to dehydrates from lack of water – in wet soil ! Although the simple answer is soil borne funguses - the true cause is over watering.  

Overwatering - or watering too frequently

Prolonged exposure to wet soil will cause roots to die back due to a lack of oxygen. Yes, those roots need oxygen !    As they die, they decay. The soil funguses (which had been dormant) in the soil now suddenly flourish, attacking the roots and causing the rot.  This rot spreads to healthy roots and kills them as well. Sometimes even the foliage.  

blackened root from fungal attack

 

Erwinia species go one step further and liquefy the foliage tissue ! Very common in Phalaenopsis orchids.

There is not much you can do other at this point other than let the soil dry out and hope the plant recovers. I have read articles s promoting repotting and changing the soil or treating with hydrogen peroxide, but over the 40 years I have been diagnosing plant problems I have found none of these methods to be very successful.

You could use a fungicide but they are water based - so you are now adding water to the soil again – perpetuating the problem. Besides - most home owners can't purchase specific fungicides to treat the soil.

This is why I emphasize Prevention – and why I focus on learning about over watering.  

So what is over watering ?

Every time you water, the weight of the water itself pushes the air (with the oxygen) out of the soil. Over time (a few days to weeks) the water is used up, the soil dries out a bit, and air returns to the pockets and the spaces in the soil.  As air returns it brings back the oxygen. If you water again before the oxygen returns you are in fact suffocating roots.

To reduce the time when the soil has low oxygen (and thus reduce the risk of rot) you have to get a handle on the frequency of watering - this is the key to success.  

Here is my method:

Water like a rainstorm and saturate the entire soil volume.  Let me put it to you this way.  You water a fern and a cactus the same way - like a rainstorm - get the entire volume of soil saturated. Water all around the pot and not in one spot. Let it drain completely until it has stopped dripping. Water again when the soil has sufficiently dried out.

Simple ! Well ... not really. It gets complicated ! (doesn't everything).

That certainly works for a small table top plant you can take to the sink and douse with water then let it drip away the excess water. But for bigger plants, or those in heavy pots you have to water where they are.

Here are my tips for larger plants:

Make sure the plant is potted in a container that drains. If you are not into that ugly green plastic pot the plant is growing in you can put it inside a decorative one with a saucer inside.  Just make sure there is plenty of room for you to be able to see inside and check the saucer for excess water.

Water sufficiently to saturate the entire soil volume.  This means you have to figure out the soil volume (math alert !).  Your goal is to provide enough water to get all the soil wet and have very little left over in the drainage saucer. A rule of thumb is about  ¼ of the soil volume. Start on the low end and add more water as needed to saturate that soil. Learn how much water to use – and remember it varies pot to pot.

Water all around and not just in one spot.  Water will by nature drip straight down due to gravity.  By dribbling the water all around the top you are able to get all the soil wet.    Watering in one  spot will also leave other areas of soil too dry and those roots will die.

After you water, wait 20 minutes and remove any excess water from the saucer. Use a turkey baster or a plastic tube, even a sponge will work.  

When to water again ?

The next time you water (Frequency) will depend on what that plant is accustomed to in nature.  In other words - where it evolved.  Think rain !

Some like to dry out completely between watering (rain) events.  In a desert it could be months for a cactus.   OR weeks for a Dracaena marginata on the Canary Islands.

Others like to reach dryness but never dry out completely  -  a week to a few days for a peace lily  in a less rainy tropical coastal forest floor.

Ferns never really like to dry out - neither do many palms - they get rained on frequently in a rainforest !

Remember - the frequency will also heavily depend on the temperature, humidity, amount of light, and ventilation. It can also vary depending on where you have your plant located in your home or office.

For example - a cactus could wait 3 months in a sunny corner in its plastic pot, but only 3 weeks if its in a clay pot on a south facing window.  Whatever it is you need to wait until that soil has become bone dry ! 

For a fern that could be 1 week in a north window or everyday in a clay pot in a west window !

Bottom line

 There is no way around it – you either learn what the plant wants and needs based on where it is and what its planted in - or you hire Plant Specialists to do it for you !!!!!

We Know.

GREENING NEW YORK FOR OVER 52 YEARS !

Article written by our Staff Horticulturist, Peter B Morris, BSc, MSc, MBA

All photographs used with permission from @SHUTTERSTOCK