Leaves

• One of the first signs of over-fertilization is that a plant's leaves will become darker, and often thicker. Some leaves may even feel leathery to the touch. This typically means the plant is receiving too many nutrients, and an over-concentration of nutrient solution is to blame. If you are feeding the plant a liquid nutrient solution, you will need to further dilute the mix in the future.
  
  

Wilting

• Over-fertilization can cause the leaves of a plant to wilt, despite regular watering. A high concentration of nutrients around a plant's roots affects its ability to take in water, thus the plant begins to wilt. Wilting is apparent when leaves become limp and begin to curl underneath.
  
  

Discoloration

• Further over-fertilization will cause the edges of leaves to display discoloration. Green leaves will become faded and blotchy. Some leaves may even start to show tip burn. This problem can be identified by yellow or light brown areas around the edges of leaves that start to become brittle if the over-fertilization continues.
  
  

Growth

• Plants that are receiving an over-concentration of nutrients, and therefore not enough water, will eventually slow down or stop growing altogether. Flower buds will not bloom, fruits and vegetables will fail to become ripe, and leaves may even begin to defoliate if over-fertilization continues.