High N fertilizers can be applied just a few weeks before a special occasion requiring a deep green lawn without harm if the lawn is basically healthy. In general, do not fertilize a newly potted plant or one that is about to enter dormancy. Resume fertilization when new growth starts. Deformed terminal buds, usually coupled with failure of the terminal bud to grow. Reduced root growth.
Some plants turn black, or show dead spots in leaf midribs.
Becomes fixed as an unavailable form in acid, peaty soils. Can be easily confused with N deficiency. Leaves get thick, curl, become brittle. Terminal buds die, leaves chlorotic, stunted growth. Youngest leaves die.