compostmike said:

That looks more like localized stress on older lower fan leaves than a full plant problem. The rest of the plant looks pretty decent from the photo.

With outdoor soil and that dry heat, I’d look first at the root zone and leaf position before blaming a single nutrient. Lower fans can get cooked, rubbed on the pot edge/cage, shaded, or go through wet/dry swings faster than the top growth shows. Once that middle tissue is damaged it won’t green back up, so the useful part is whether it keeps moving into newer leaves.

I’d check undersides for mites/thrips just to rule that out, then watch the newest growth. If the tops stay clean and only a couple old lower leaves did this, I wouldn’t start hammering it with bottled fixes. Keep the soil biology steady, avoid big swings in moisture, and let the plant tell you over the next few days.

What soil mix is it in, and has it been drying hard between waterings?

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BartinFelch said:

1/3rd coco, soil, pearlite. using grow dots. I f'd-up and mixed unbuffered coco coir in and was getting 3.3 ph readings, and all sorts of shit. Now I'm overly freaked. I thought of a cal-mag watering (the spots start rust colored)?

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compostmike said:

3.3 pH is the part I’d be more worried about than the rust spots themselves.

The leaf damage looks like a plant that had the root zone go sideways, not necessarily “needs more cal-mag right now.” Unbuffered coco can tie up calcium/magnesium and mess with the cation balance, and if the medium was actually sitting that acidic the roots and microbes were probably stressed pretty hard. Those older fans are just where it showed first.

I wouldn’t hammer it with a bunch of fixes on top of Grow Dots. If you do use cal-mag, keep it light and make it more about buffering/stabilizing the coco than feeding heavy. I’d water at a sane soil/coco pH, let the pot dry evenly but not bone dry, and watch the new growth for 3-5 days. Damaged leaves won’t repair.

If that 3.3 was runoff, I’d do a proper slurry test too. Runoff can lie, especially in a mixed soil/coco/perlite pot. If the slurry is still crazy low, then I’d be thinking gentle pH correction/root-zone stabilization before chasing individual deficiencies.

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