Not all plant problems are caused by insects or diseases. Sometimes an unhealthy plant is suffering from a nutrient deficiency. Plant nutrient deficiencies often manifest as discoloration or distortion of the leaves. Unfortunately many problems have similar symptoms and sometimes it is a combination of problems. Be sure you eliminate the obvious, like poor drainage or compacted soil, before you kill your plants with kindness. But if you think your garden plants are under nourished, here's a listing of some common nutrients and their deficiency symptoms to guide you.