Yellowing in early summer (Wisconsin) usually means heat stress, nutrient deficiency, or water issues.
| Symptom | Likely Cause | Fix |
|---|
| Uniform yellow, older leaves first | Nitrogen deficiency | Fish emulsion 2×/month |
| Yellow + bolting (flower stalks) | Heat stress (>75°F) | Shade cloth, succession sow |
| Yellow + wilting, wet soil | Overwatering/root rot | Improve drainage, water less |
| Yellow + dry soil | Underwatering | Deep soak, mulch |
| Interveinal yellow (green veins) | Iron/magnesium deficiency | Chelated Fe/Mg foliar spray |
Immediate Actions
- Apply liquid fish fertilizer (5-1-1) per label – fast nitrogen.
- Ensure morning sun only; rig 30% shade cloth for afternoon.
- Water deeply when top 1" dry; don't let wilt.
- Sow new cilantro seeds every 2 weeks (it bolts fast).
- Cut parsley flower stalks; fertilize every 3 weeks.
Soil Test
If persistent, test soil (pH, N-P-K, micros). Amend based on results.
Cool-season herbs in summer need extra care—feed, shade, succession plant.
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