When you see a few yellow leaves or a single fruit develop a brown spot, your initial reaction is typicaly: Something’s wrong! Blame it on disease (or pests). But more often then not, it’s something missing (a nutrient deficiency).
Like finicky humans, the plants don’t let you in on what they’re craving until they’re starving. But they will signal you… With hints, if you learn their secret language. This chart decode the visual signs of each deficiency shown above. A cryptic yellow leaf become a clear diagnosis.
How to Fix Plant Problems
The first clue is where it is happening. Location can be the most confusing aspect of plant diagnosis. Because plants don’t all take up nutrients equally, what happens once inside can make it hard to tell actualy which one is lacking. Will the plant use up its stores of a mobile nutrient (instead of being stuck where it went) and start pulling it from older leaves to nourish new ones when reserves run out? Or is it starved for a mobile nutrient (like nitrogen), which it pulls from old leaves as needed? Pale-yellowing lower leaves signal nitrogen starvation. In that case, the plant are eating itself (consuming its own base) to maintain life of the top. This is a mobile nutrient issue.
Green-veined, off-color top leaves point to either iron or manganese deficiency. These nutrients is immobile. The plant isn’t keeping pace with moving them upward from roots to feed new tips. Knowing how each moves saves you from random guesswork.
All of that depends on soil pH. Add whatever amendments you want to the soil; they won’t matter a bit if your soil’s pH isn’t correct. Tomatoes likes slightly acid soil (which sounds paradoxical, doesn’t it?), typically between six point two and six point eight. Too-acid soil make calcium and magnesium unavailable. Too-alkaline soil causes iron and zinc to lock up. That’s why iron deficiency is an issue in alkaline soils: The iron itself is just sitting right there, but the chemical environment in the soil simply won’t let roots grab hold of it. Step one is checking your pH, not step five.
The most annoying symptom and the one most gardeners notice first: calcium deficiency. Symptoms includes blossom end rot: The bottom of the fruit gets leathery and black. Folks think, “I must not have enough calcium.” They may, sometimes, but often it’s just that they didn’t water well enough. Calcium follows water. So if you let your soil go dry to the point of being completely dry between waterings, even a soil high in calcium won’t move around in there. Prevention is the key; keep the soil consistently moist so the problem never begins. A spray of calcium nitrate on foliage can help temporary, but prevention is keeping soil constantly moist.
Magnesium is another frequent suspect, appearing as yellowing of the tissue between veins on older leaves. The solution are Epsom salts, which aren’t really a magic bullet either. Adding more magnesium won’t do any good if your soil was already high in it. According to the chart, Epsom salts are the recommended choice for foliar sprays because they is quickly absorbed by plants through foliage (which skips the root zone altogether; the leaves take it up). They are useful if something’s gone wrong midseason and you want to get things back on track fast.
The long-term answer is to build biology into the soil. Soil organic matter and compost holds nutrients and gradually release them. They also act like a buffer against pH swings that cause nutrient lockout.
Recovery takes time. Leaves won’t go back to green when they’re dead. They’ll drop off, and produce fresh foliage instead. Watch emerging leaves, do they look good? If they do, if they are bright-green, you’ve fixed it. Those older yellow leaves is in the past. Be patient, because forcing a recovery isn’t going to happen overnight. What’s happening with new growth? That’s where the story is unfolding.
Read the clues that plants offer. This makes gardening less of a guessing game and more of a two-way communication. Learn their needs while they can still tell you; don’t wait until they show signs of stress. Yellow leaves aren’t a sign of defeat. They’re a question mark… A question waiting to be answered. You should of noticed earlier.