Underfertilization

• Nutrient deficiencies can limit the plant's ability to grow and cause its leaves to turn yellow. This often occurs because the soil pH is too high, which converts the nutrients into salts that cannot be absorbed by the plant's roots.
  
  

Overfertilization

• If you give your plants too much fertilizer, the roots or tips of the plant may turn brown from the excess nitrogen. This is known as "fertilizer burn" and can be corrected by flushing out the soil with water.
  
  

Pollution

• As fertilizer breaks down, the nitrogen particles change into nitrates that seep down into the soil. These nitrates can contaminate the local drinking water if they reach the groundwater or nearby streams. Phosphorus increases algae growth in streams, which chokes off the oxygen supply to fish.