Nutrient deficiencies are one of the most common — and most misunderstood — problems in greenhouse farming. They don’t always show up as dramatic symptoms. Sometimes it’s just a slight yellowing, a subtle curl, or a slow-down in growth. But if you catch them early, you can correct them before they affect yield. This post gives you a simple, field-tested method to diagnose deficiencies in under 60 seconds — no lab, no guesswork, just your eyes and a checklist.