Sunday, June 28, 2009

Diagnosis: Root Rot

Recently someone came to me with a problem. Their orchid lost its buds soon after purchase, and hasn't bloomed or really done anything since. Since there are many many reasons for bud drop, we started discussing what might be happening. Fortunately, the owner sent me this photo of her plant. Immediately I could tell the plant has root rot, which is ultimately the cause for its listlessness.

Photo provided by Tatyana.

Root rot is one of the most common diseases with orchids. Pretty much everyone has had to deal with it at some point or another. The most sad part is that new orchid growers, who are often not even at fault, mistakenly believe they "can't grow orchids" because they have simply purchased a hardware store plant that already has root rot without knowing. Today I am going to teach you how to diagnose, treat, and prevent root rot.


* Floppy, listless leaves. Although phalaenopsis leaves can be healthy and still bend or flop over in order to take the most advantage of the light, they should still be pretty tough and thick. These leaves, if touched, would feel withered and soft. Notice also the wrinkles on the leaf top-most in the photo. This plant has not been able to absorb enough water into its little body.

* Exposed roots, while healthy, are also withered and possibly brittle. Exposed roots are normal with phalaenopsis plants. However, they should be plump and active. (its OK to have some that are shutting down, since getting rid of old parts is normal for plants). This plant has been sacrificing water and sugars in the roots and other parts of the plant to live.

* Many to all in the media will be black and squishy - dead and rotting. This is the defining characteristic of the disease.


* Media appears to be a normal potting soil, which with a few exceptions is not really an appropriate potting mix for orchids. Exceptions include true terrestrial orchids (e.g. "jewel" orchids like Ludisia discolor), and people with experience using a media like this. There are some top growers who use a chunky coarse peat-based mix with great success, but for most people it stays too wet. It also requires regular repotting, since as it breaks down it will hold even more water. Staying wet too long leads to root rot, just like walking around with your feet wet might lead to foot fungus. Note also that this type of media has been popular with large nurseries growing plants for the "pot plant" trade, where plants are expected to be purchased just for the flowers and then tossed.

* In some cases, media may also just be a very degraded typical orchid mix. As noted above, rotting media starts to hold more and more water, increasing the risk for root rot if adjustments in the watering regeme are not made or the plant is not repotted.


* Pull the plant out of the pot immediately, removing all old media and dead roots. Dead roots will be squishy or papery and black. Leave any firm, healthy roots. Hose off plant.

* Cut or break away the base of the stem if it appears to be infected. Dust cut surfaces with cinnamon or sulfur.

* Optional: Spray plant with fungicide. > I generally do not do this for root rot as fixing potting problems are generally all that is needed to stop the spread of the problem.

* Leave to dry overnight.

* Optional: Soak entire plant in a warm solution containing a low concentration of sugar, a few drops of Superthrive (B vitimin / NAA coctail), and a low concentration of chemical fertilizer. > I have only tried this approach a few times. I cannot say if this actually confers an increase in survival rate, but am providing it for completeness.

* Repot plant into appropriate media. For rehabilitation of difficult cases I suggest using sphagnum moss, which has mild antibacterial properties. Prewet it and pack only loosely around the roots. Wetting any existing thoroughly will help them be more flexible. In this case, the only remaining roots were the surface roots. These were placed in the media so that they can better serve the plant during its recovery.


Plants with root rot can survive. Minor cases generally always survive. A case such as this will, not surprisingly, have a lower survival rate. Expect the more severe cases to take a year or more to recover fully.


* Repot your plants regularly to keep the media fresh. This will be approximately every 1-3 years depending on plant type, media type, and your watering habits. Repotting means removing old media and replacing with new. It does not always mean moving up in pot size. In some cases it can even mean a reduction in pot size.

* Know what is an appropriate watering regimen for your plant. This will depend on what type it is. If it is something unfamiliar to you, ask the grower you're getting it from. Also, hang on to your plant labels in case you have more questions down the road. Being able to tell other growers exactly what you have will make it easier for them to help you. Note that watering amount is not the issue. Watering frequency is. When it is time to water, water heavily and let it drain well. Letting a plant sit in water is generally not a good idea.

* If you buy from a non-orchid grower (such as from a perennial specialist) or hardware store, repot it immediately or as soon as possible. If it comes in "dirt", repot immediately even if the plant is in bloom. At the very least it is a good idea to pull a plant out of the pot and look at the roots and condition of the media when you get home with any plant.


* Watering too little can give the plant the same appearance. Definitive diagnosis here lies in the condition of the roots. Watering too little will of course not cause rot.

* High salt buildup can also cause a similar appearance, again minus the root rot. This essentially would be a dessication case. Salt buildup rarely reaches critical levels, however. You can identify it by a peculiar appearance of the media, including crusty deposits. This can generally be fixed by repotting, then prevented by watering occasionally with rainwater or RO water if fertilizer (or by fertilizing less!), or occasionally with Epsom salts (Magnesium Sulfate) solution if the cause is hard water.

Other helpful articles on this blog you may find helpful-
Basic Phalaenopsis Culture
Reasons for Plant Collapse in Phalaenopsis
How to repot a Paph Orchid


JVinOZ said...

Hey Julia. Love this diagnosis and solution. I am the editor of the Orchid Species Society of Victoria Newsletter in Melbourne Australia and would like to reproduce this in our Newsletter for members who don't have computer access. Can you please reply to me via my Flickr account where my e-mail address is located at the bottom of my profile page?
Many thanks

Anonymous said...

Thanks Julia for your kind advise. I have repotted my orchid in orchid media and it actually looks happier now (the central tiny leaf is green and perky). Question - how do you actually water it in the pot with holes and filled with this bark media? The water just goes right through it...


SapphireChild said...

Just apply lots of tepid water to the top of the media and let it drain. Most of it does go through, but some will wet the media and the roots. You can test it with your finger- you should be able to feel dampness in the pot even a few inches down. If not, water some more. Again, water plenty when its time to water, but allow an appropriate interval between watering to let the media dry off some. In bark for a phalaenopsis that would be about 2-3 inches down or half the pot height, whichever is smaller.

Anonymous said...

I recently came accross your blog and have been reading along. I thought I would leave my first comment. I dont know what to say except that I have enjoyed reading. Nice blog. I will keep visiting this blog very often.


Paula Cimba said...

I was wondering about all the dead, dried roots at the top on my phals that have been happy (I think) and healthy, reblooming about every 4-6 months, one producing a keiki which I have just repotted (keeping my fingers crossed). Should I still repot, and cut off these dry brown roots? Many thanks in advance, for your advice.


SapphireChild said...

Roots on the surface can sometimes become dessicated where humidity is very low. Is this the case or do they seem "empty"? In either case, you can remove them or not, they shouldn't cause any harm to your plant. If the leaves look good - glossy, thick - the plant is probably fine.

Even so, it is a good idea to repot every couple years if you are using any media based on organic matter - bark, moss, whatever. Also, when in doubt about a plant, the best thing to start with is knocking it out of the pot for a look at the roots. Too soon repotting doesn't hurt, especially if you always match the pot size to the roots.

Gina said...

My orchid seems to be happy. I noticed, however, that some roots have gotten hard. Should I remove them?

SapphireChild said...

@Gina -
I guessing you are differentiating between "firm but plump" of young roots and "hardened and sometimes flattened" of old roots. If they are hard, they are not rotting. Sometimes roots along the top of the can dry out, and sometimes older roots and particularly older roots that have "attached" to a surface will become hard, almost woody with age. They don't do any harm, and may still move water.