| N | The chemical symbol for nitrogen. |
| nastic movement | A movement of a plant part (such as a leaf) not caused by an external stimulus. |
| native plant | A plant indigenous to a specific habitat or location. |
| natural selection | The action of the environment on organisms such that those better able to survive environmental stress are more likely to survive and reproduce. |
| naturalize | (1) To design a garden with the aim of creating a natural scene. Planting generally is done randomly, and space is left for plants to spread at will. (2) The process whereby plants spread and fill in naturally. |
| necrosis | Tissue death. |
| nectar | A sugary fluid secreted by some flowers. |
| nectar guide | A contrasting color pattern on a flower that guides pollinators to the nectar. |
| nectary | A gland secreting nectar. |
| nematocide | A material that kills or protects against nematodes. |
| nematode | A microscopic roundworm, usually living in the soil. May feed on plant roots and can be disease pathogens or vectors. Others are beneficial parasites of insect pests. |
| nitrate (NO3–) | A plant-available form of nitrogen contained in many fertilizers and generated in the soil by the breakdown of organic matter. Excess nitrate in soil can leach into groundwater. See nitrogen cycle. |
| nitrifier | A microbe that converts ammonium to nitrate. |
| Nitrogen (N) | A primary plant nutrient, especially important for foliage and stem growth. |
| nitrogen cycle | The sequence of biochemical changes undergone by nitrogen as it moves from living organisms, to decomposing organic matter, to inorganic forms, and back to living organisms. |
| nitrogen fixation | The conversion of atmospheric nitrogen into plant-available forms by Rhizobia bacteria living on the roots of legumes. |
| node | The point on a plant where a branch, bud, or leaf develops. On younger branches, it usually is marked by a slight swelling. The space on the stem between nodes is called an internode. |
| nonpoint source | A relatively small, nonspecific source of pollutants that, when added to other sources, may pose a significant threat to the environment. See point source. |
| nonselective pesticide | A pesticide that kills most plants or animals. |
| N-P-K | The acronym for the three primary nutrients contained in manure, compost, and fertilizers. The N stands for nitrogen, the P stands for phosphorus, and the K stands for potassium. On a fertilizer label, the N-P-K numbers refer to the percentage of the primary nutrients (by weight) in the fertilizer. For example, a 5-10-5 fertilizer contains 5% nitrogen, 10% phosphorous, and 5% potassium. |
| nucleus | The organelle (structure) within most living cells that contains the chromosomes which controls various cellular processes, including division into new cells. Bacteria and viruses do not have a nucleus; their chromosomes are distributed throughout the entire organism. |
| nutrient | Any substance, especially in the soil, that is essential for and promotes plant growth. See macronutrient, micronutrient. |
| nymph | The immature stage of an insect that undergoes simple metamorphosis. Usually similar in form to the adult. |
