| fallow | To keep part of a garden unplanted or in a cover crop during the growing season. |
| family | A broad group of plants with common characteristics. |
| fasciation | Distortion of a plant that results in thin, flattened, and sometimes curved shoots. |
| feeder roots | Fine roots and root branches with a large absorbing area (root hairs). Responsible for taking up the majority of a plant’s water and nutrients from the soil. |
| fermentation | The partial breakdown of food molecules to yield ethyl alcohol, carbon dioxide, and energy. Fermentation occurs in the absence of oxygen. |
| fertility (soil) | The presence of minerals necessary for plant life. |
| fertilization | (1) The fusion of male and female germ cells following pollination. (2) The addition of plant nutrients to the environment around a plant. |
| fertilizer | A natural or synthetic product added to the soil or sprayed on plants to supply nutrients. |
| fertilizer analysis | The amount of nitrogen (N), phosphorous (as P2O5), and potassium (as K2O) in a fertilizer, expressed as a percentage of total fertilizer weight. On the N-P-K fertilizer label, the percentage by weight of nitrogen (N) is always listed first, phosphorous (P) second, and potassium (K) third. |
| fiber | A long, thick-walled cell that dies at maturity. |
| fibrous root | A root system that branches in all directions, often directly from the plant’s crown, rather than branching in a hierarchical fashion from a central root. See taproot. |
| filament | The stalk supporting a flower’s anthers. |
| flagging | Loss of turgor and drooping of plant parts, usually as a result of water stress. |
| floricane | Second-year growth of caneberries. Produces fruit on laterals. |
| flower | The reproductive branch or structure of an angiosperm plant. |
| foliar fertilization, foliar feeding | Fertilization of a plant by applying diluted soluble fertilizer, such as fish emulsion or kelp, directly to the leaves. |
| food | An organic substance that provides energy and body-building materials, especially carbohydrates, fats, and proteins. |
| force | To bring a plant into early growth, generally by raising the temperature or transplanting it to a warmer situation. Tulips and paperwhites are examples of plants that often are forced. |
| form | (1) A naturally-occurring characteristic different from other plants in the same population. (2) The growth habit (shape) of a plant. |
| formal | (1) A garden that is laid out in precise symmetrical patterns. (2) A flower, such as some camellias, that consist of layers of regularly overlapping petals. |
| frond | Specifically, the foliage of ferns, but often applied to any foliage that looks fern-like, such as palm leaves. |
| fruit | The edible portion of a plant that is closely associated with a flower. Botanically, a fruit is a ripened, mature ovary. |
| fruiting habit | The location and manner in which a fruit is borne on woody plants. |
| fungicide | Any material capable of killing fungi. Sulfur and copper sulfate are two common mineral fungicides. |
| fungus | A plant organism that lacks chlorophyll, reproduces via spores, and usually has filamentous growth. Examples are molds, yeasts, and mushrooms. |
