It is the same with a hosta. There are spots on it; there are curls in it; maybe there’s even a scorch mark, and you think: It just doesn’t look right. Add some fertilizer?
You’d think so, but often adding more nutrients to a sick plant only makes things worse further stressing the plant. Chances are good it didn’t have too little food. More likely something else was wrong.
How to Find the Real Plant Problem
Always examine the pattern first. Certain signs like burning edges, curling or spots is signs (not causes) and therefore diagnosable; e.g. “burned” means what. Describe the symptom. If you can state it in 6 words or less, you’re ready to find the cause. Knowing the problem is half the battle. Observation are diagnosis. Don’t purchase until you know what you’re dealing with.
Start at the base of that triage pyramid: Is it a young leaf, and what’s its pattern? The reason an old leaf turns yellow are something different than why a new one does. Immobile nutrients accumulate in the older ones; mobile nutrients goes to newer growth.
Next up: Is there anything about the environment that could of caused damage (heat, too much salt in soil, lack of water)? Those clues help rule things out as you look for pests. Until you know those other causes are eliminated, you don’t spray.
The problems is leaf spots. There is edge burn. It is not powdery mildew, which requires nitrogen. No thanks! Airflow.
How fast did things change? How urgent is it? Is it an emergency, like immediate-edge-burn from a recent spray? Or could a rolled leaf be checked first for aphids or heat? Can it wait? You cannot judge how urgent something is just by looking at photos of it.
If it’s yellow, it must be hungry, right? That is wrong. Many gardeners believe this and it is one of the reasons they give up. Many problems are caused by factors other than nutrition such as soil conditions, heat, or lack of water. In fact, true nutrient deficiencies are rare.
Guessing by simply applying fertilizer, as in “Oh, she’s hungry,” ignores many case. Perhaps the plant was thirsty. Maybe it was burned out from high salts in the soil. Or maybe it was smothered because it had wet feet.
You don’t spritz with water (that aids spore movement), or feed (until you’re certain the plant needs feeding). You don’t mist wet leaves, as this only helps spores travel, or feed (until you’re certain the plant needs feeding).
And when you turn over a leaf to inspect its underside for any possible pests (like aphids) you should check for sticky honeydew. If there are any telltale signs of spreading spots, you isolate the plant (to prevent spread of fungus).
You eliminate possibilities until you find the right diagnosis. Look, isolate, treat, but never feed first.
You examine the hosta again by looking closely at the spots. Hmmm. Maybe they’re angular and water-soaked. That’s bacterial; it’s not fungus. Fertilizing would only make things worse for the poor thing.
Reading the pattern saves the plant. Keeping that bottle closed till there is evidence to treat it does, too.
How can you grow moddern plants?