F1 hybrids First-generation plant, obtained from crossing two selected pure-breeding parents to produce uniform, vigorous, and high-yielding offspring. Seed from F1 hybrids does not come true.

F2 hybrids: plants that result from self- or cross-fertilisation of F1 hybrids; they are less uniform than their parents.

Falls The pendant or horizontally placed tepals or petals of irises and some related plants.

Family A category in plant classification, a grouping together of related genera, for example the family Rosaceae includes the genera Rosa, Sorbus, Rubus, Prunus and Pyracantha; the family Iridaceae includes the genera Iris, Crocus, Dierama, and Crocosmia.

Fastigiate With the branches (usually of trees and shrubs) growing vertically and almost parallel with the main stem.

Feathered Of maiden trees that have several lateral branches (“feathers”).

Fertile (of plants). Producing viable seed: shoots bearing flowers are also said to be fertile shoots as opposed to non-flowering (sterile) shoots.

Fertilisation The fusion of a pollen grain nucleus (male) with an ovule (female) to form a fertile seed.

Fibrous 1) Of roots, fine and often branching and dense; 2) Of loam, containing fibre derived from (dead) grass roots.

Filament The stalk of the stamen which bears the anther.

Fimbriate Of part of a plant that has a fringed margin. Plant organs with a fringe of hairs are said to be ciliate.

Floating cloche Lightweight sheet, usually of woven polypropylene (fibre fleece), placed over a crop, which is lifted up by the plants as they grow. It provides some frost protection while allowing water and light penetration. Also known as floating mulch.

Floret A (generally) small flower in a flowerhead consisting of many flowers.

Flower The part of the plant containing the reproductive organs usually surrounded by sepals and petals. The basic flower forms are:

• single, with one row of usually four to six petals:
• semi-double, with two or three times the normal number of petals usually in two or three rows:
• double, with more than the normal number of petals in several rows with few or no stamens produced:
• fully double, flowers usually rounded in shape, with densely packed petals and with the stamens obscured or absent.

Flowerhead A mass of small flowers or florets that together appear to form a single flower as in members of the family Compositae.

Foliage The green leaves of a plant.

Force To induce plant growth, usually of flowers or fruit by control of the environment, normally by increasing the temperature.

Forma (f.) A variant within a species usually distinguished only by minor characteristics. Clematis montana f. grandiflora is a larger-flowered, more vigorous form of C. Montana; also loosely used for any variant of a species.

Formative pruning A method of pruning that is carried out on young trees and shrubs to develop the basic branch structure of the desired form or shape.

Foundation planting The basic, and usually permanent structural and shelter planting of trees and shrubs in a garden.

Framework The permanent branch structure of a tree or shrub: the main branches that determine its ultimate shape.

Framework plants The plants in a garden that form the basis or structure of the design.

Frame-working (of fruit trees) Pruning back all side growths to the main framework and grafting scions of a different culture onto each main framework branch.

Friable (of soil) Of a good, crumbly texture: capable of forming a tilth that can be worked easily.

Frond 1) The leaf-like organ of a fern. Some ferns produce both barren and fertile fronds, the latter bearing spores. 2) Loosely applied to large, usually compound leaves such as those of Palms.

Frost pocket A site, often a hollow, where cold air gathers, that is subject to severe and often prolonged frosts.

Fruit The fertilised ripe ovary of a plant containing one to many seeds, for example, berries, hips, capsules and nuts; the term is also used of edible fruits.

Fruit set The successful development of fruits after pollination and fertilisation.

Fungicide A chemical that kills fungi especially those responsible for various plant diseases.