Excessive nitrogen (N) application produces 'too rapid' growth which results in softness of tissue and general plant weakness. While N spurs green growth, flowers and seed formation will be greatly reduced. Plants with excess N are more susceptible to disease and injury.
Test soil before adding fertilizers with N. Use organic or chemical fertilizers with N carefully and avoid adding too much to soil. If after testing it is determined that you have excessive N in your soil, consider applying a layer of mulch to it. Cheap, dyed mulch made of soft woods is particularly effective in using excess N in the soil as it breaks down. Alternately, plant plants with large N requirements, such as squash, cabbage, broccoli or corn. These plants won't look at all healthy, but they can use up large amounts of N in the soil.