New York City Gardener Practice Exam

Fertilizer is formed from minerals in salt form, and when too much is applied it becomes a salty solution in the soil. That high salt concentration creates osmotic pressure around the roots, making it harder for the plant to take up water. Water may be pulled out of root cells or into the salty soil, leading to dehydration, tissue burn, and damaged feeder roots. With the roots stressed, the plant can’t absorb water and nutrients effectively, which is why over-application harms the plant.

Sugar isn’t how fertilizers typically work; lime changes soil pH rather than causing the osmotic damage associated with fertilizer salts; and water by itself doesn’t supply the needed nutrients and doesn’t create the same osmotic injury as excess fertilizer salts.