Gardening Definitions (G-I)

Genus
The category in botanical classification below family. A genus is a group closely related plants known as species. All the species of beech trees (for example), are grouped under the genus Fagus. Related genera are grouped in turn into a family, in this case Fagaceae. The common beech is identified by a genus and a species name, Fagus sylvatica. A natural variety is identified by a third name, such as Fagus sylvatica var. heterophylla, and a cultivated variety (or cultivar) by quotation marks, as Fagus sylvatica 'Dawyck'. A cross (or hybrid) between two species is identified by a multiplication sign: for example, the hybrid willow Salix x rubens
Germination
The initial stage of a plant's development from a seed. Germination periods vary: given the right conditions of temperature, moisture, light and oxygen, it may occur within days or take weeks or months.
Glabrous
Smooth or bare - used to describe a part of a plant that is hairless.

Glaucous
Describing the grey-blue colour of some plants, or the grey or white waxy bloom on them. An example is the white bloom on the leaves of some brasicas, particularly cabbages, and succulents such as sedums.

Grafting
Propogation plants by joining a stem or bud of one plant to the root of another so they unite to form a new individual. It is widely used in cultivating fruit trees and roses.

Habit
The characteristic shape and growth form of a plant.

Half Hardy
Frost tender species of plants that can only be grown in the open reliably during summer - for example, canna and French and African marigolds.

Half Standard
A tree or shrub, usually with a single stem growing 75cm-1.2m high before the head branches.

Hardening Off
The gradual acclimatisation of tender and half hardy plants, grown under heated glass or other forms of protection, to outside conditions. Plants are usually placed in a coldframe in late spring, with air gradually admitted until the lights of the frame are left off entirely.

Hardy
Plants which survive frosts in the open, year by year.

Herbaceous
Any plant that does not form a persistent woody stem. Botanically, the terms applies to annuals, biennials and perennials - but by common usage is chiefly associated with perennials which die down in autumn and reappear the following spring.

Hose in Hose
An abnormal floral mutation in which flowers appear to grow in pairs, one arising from the centre of another. Primrose and polyanthus are examples.

Humus
The dark brown residue from the final breakdown of dead vegetable matter. The term is often used to describe partly decayed matter that is brown and crumbly, such as well made compost or leaf mould.

Hybrid
The result of crossing two distinct varities or, occasionally, genera. Hybrids may either show a blending of characteristics from each parent or favour one more than the other.

Incised
The margins of the leaf, stipule or bract that is deeply and sharply toothed or lobed.

Inflorescence
The arrangement of flowers on a stem, often referred to as a flowerhead.

Inorganic
A chemical compound or fertiliser that does not contain carbon. The term is applied to synthetically produced fertilisers, although some naturally occurring plant nutrients have inorganic origins, as, for example, the mineral fertiliser rock phosphate.