Weed Plant Problems: Diagnose by Photo

Weed plant problems almost always show on the leaves first, and most of them trace back to three causes: water, pH and light. This section is built to be used with a sick plant in front of you. Every page leads with photos, because you diagnose by what you see, not by what you think you did.

I have looked at thousands of reader photos of sick plants. The plant is usually fine. The grower has usually changed four things at once and now cannot tell which one worked.

How to use the weed plant problems pages

Start with the leaf symptom chart. It sorts symptoms by where they appear (bottom leaves or top, edges or center, spots or whole-leaf color change) and sends you to the right page. Yellow leaves is the page most people need, because yellowing has at least six causes and the position of the yellow tells you which. Bud rot is the one to read before you need it, since by the time you can see it you have already lost that cola.

Each problem page follows the same order: what it looks like, what else looks like it, the cause, the fix, and how to keep it from coming back. The "looks like this, but is not" strip on each page exists because a deficiency, a lockout and root trouble can all produce the same leaf.

Check pH and water before anything else

Before you buy a supplement or change your nutrients, check two things. First, the pH of what goes in and what runs out: 6.0 to 6.5 in soil, 5.5 to 6.2 in hydro or coco. Most "deficiencies" are lockout, meaning the nutrient is in the pot but the roots cannot take it up at the wrong pH. Second, how wet the medium is. Lift the pot. Overwatering shows as drooping, yellowing and slow growth, and it is corrected with patience, not with more of anything.

Only after pH and water are ruled out should you look at feeding, and only after feeding at the environment. VPD covers the temperature and humidity side, which explains a lot of curled and crisped leaves that get blamed on nutrients.

Change one thing at a time

This is the discipline. Change one variable, wait three to five days, look again. If you correct pH, flush and add cal-mag on the same day and the plant improves, you have learned nothing for next time. If it gets worse, you have three suspects. The problem pages here give you one fix each, in order of likelihood, so you can work through them without guessing.

If you have a photo and a question, send them to Dear Danko. Photos in white light, whole plant and close-up, make the difference between a guess and an answer. Once the plant is healthy again, the grow guide is where you keep it that way.

Cultivation is for adults where it is legal.