Richard C. Bogren, Kirk-Ballard, Heather
LSU AgCenter Horticulturist
Last time, we discussed plants having special characteristics due to breeding, genetic mutations and the use of viruses to manipulate their appearance. This week, we will take a look at how to determine what’s going on when plants look fatally ill or are dead.
One of the classic and common symptoms that signifies something is just not right is wilted, weeping plants that turn from green to yellow and sometimes crispy brown. Let’s consider the evidence.
One of the most common causes of plant death is water. More specifically: too much or too little water. You might be surprised to learn it’s sometimes hard to tell the difference. Grab your clipboard and magnifying glass, put on your deerstalker cap and let’s get to the facts of the case.
Most folks think it’s simple to diagnose plants that have wilting leaves or drooping plants that are beginning to fade from a dark green to pale green or yellow. That’s easy, right? Clearly, the plant needs water. Case closed. Let’s wrap this one up. We’ll answer questions after we break down the crime scene.
Hold up, not so fast. Pump the brakes. Did you know that the symptoms of under-watering can look just like a plant that has been over-watered? Yes, they can. First, let’s rule out for certain it isn’t dehydrated.
Here is the evidence you should be looking for to determine if dehydration is the cause. Your first clue will be dry soil. Seems intuitive, right? You would not believe how many times we have been fooled by the appearance of a plant into thinking it was dry and doused it with more water only to find it one day closer to death.
To determine if the soil is truly dry, you should go beyond the surface. Test the soil by sticking a finger in the top couple of inches. Many times, the soil surface may appear dry, but what’s going on underneath will reveal if the soil is truly dry in the root zone where plants pick up the majority of the water (and oxygen) that is transported throughout the plant. If it is a potted plant, pull the plant out of the pot and inspect the roots. Are they firm and white? Then they are healthy.
For any plant, whether potted or in the ground, bend one of the stems. Is it flexible? That is, does it snap like a dried twig or somewhat spring back? One last piece of evidence to look for before we close the case: perform a scratch test. To do so, lightly scratch one of the tender stems to remove the thin bark layer. Is the stem green or brown? If it’s green, that’s good news. Your plant still has life, and you can likely save it.
That was a close one. No calling the coroner here. Let’s water the plant. Remember, if the soil is completely dried out, it will require more water to reestablish an adequate moisture level. Get on a schedule of watering plants to prevent this from happening. Monday, Wednesday, Friday, for example, if your plant requires it. Some plants only require watering once a week. You must figure this pattern out depending on the temperatures outside and amount of sunlight the plant gets, etc.
Now, let’s consider death by drowning. Plants that are too wet can display the same symptoms as plants that are too dry. Let me explain. Plants take up water by their roots. That’s an important fact to remember.
Now, let’s look at the evidence in this case. First clue: the leaves are wilting. Second clue: the plant has begun to droop. What do we check first? That’s right, let’s check the soil. You stick a finger in the top few inches of the soil because you are a well-trained detective. It’s sopping wet. Hmmm, that’s not what you expected. The leaves are wilting. The plant is wilting. The leaves are yellowing and turning brown, but the soil is wet. Let’s test the stem. When you bend it, it’s just limp and does not spring back. Next, you perform a scratch test and do not see green, but rather you see dark discoloration. What is going on? Let’s take a look at those roots. They’re brown and soft, not firm and white as they should be. And what’s that smell? It smells like something is rotting. All this evidence points to a classic case of root rot.
Why is the plant wilting? When a plant is over-watered and the soil remains saturated, it is a perfect environment for fungal pathogens that damage the roots. The plant roots become diseased and no longer function as they should. Most folks know that plants make the oxygen that we breathe through the process known as photosynthesis in which carbon dioxide is converted to oxygen in a reaction using both sunlight and water. But did you know that plants also take up oxygen from their roots in the process known as respiration (like we do)? When the roots are damaged, the plants cannot “breathe” because the air pockets in the soil become filled with water. Essentially, the plants drown.
It is a delicate balance between wet and dry. The key is sufficient water along with good drainage. Tip the scales in either direction and you have a new case on your hands. Next week we’ll consider other classic cases of plant homicide. It can be accidental death . . . or calculated murder.
Always remember, healthy roots are the foundation for healthy plants. Reach out to your local AgCenter agent to help you positively identify plant diseases that cause root rot and to get treatment recommendations, if necessary.
This very young schefflera house plant has a healthy, white root system. Photo by Heather Kirk-Ballard/LSU AgCenter
An older potted Turk’s cap has a mature, larger, healthy and white root system. Photo by Heather Kirk-Ballard/LSU AgCenter
Drooping leaves on this azalea show symptoms of root rot. Photo by Page Langlois/LSU AgCenter