Germplasm 
A source of genetic material, such as plant tissue, which is used for plant breeding, for example for grass seed cultivar development.
Gibberellins
These are plant hormones (also known as a growth regulators) that regulate a range of plant development processes.
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Glabrous
Hairless; a generally smooth surface.
Glucose
A simple carbohydrate (sugar) product of photosynthesis, having the chemical formula of C6H12O6. This is the most basic of carbohydrates and acts as a building block for more complex carbohydrates, as well as primary (e.g. protein) and secondary metabolites (e.g. plant hormones such as gibberellins).
Glycolysis
The first step in respiration which involves the splitting of a six-carbon glucose molecule in several stages, into two three-carbon molecules of pyruvic acid. This product is then converted to ethanol and CO2 under anaerobic conditions, which can occur in waterlogged or compacted soils, or is converted to acetyl-CoA for use in the citric acid cycle, under aerobic conditions.
There is a net production of two energy ATP compounds resulting from glycolysis, whilst another 36 ATP compounds are converted from a six-carbon molecule as a result of aerobic respiration. With a lot less energy bei
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Gravitropism
The growth of plant features towards (roots) gravity or away (stem and leaves) from gravity.
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Green Manuring
The growing of crops such as clover, rape seed, mustard, vetches or rye, which is then ploughed and cultivated into the soil to add organic matter and enrich it with plant nutrients.
Growing Degree Days
A Growing Degree Day is any day in which the average temperature is above a specified base temperature, which is given for a particular subject matter. Growing Degree Days is an accumulation of these days and their values which are above the base temperature, providing an accumulated heat value.
An example might be the average temperature of a day, in say April, being 10°C, and if the base temperature is given as 5°C, then for that day it is 5 GDD. The starting period for monitoring GDD might typically be March or April, through to the end of October or November. The value of recording GDD
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Growing Degree Days (GDD)
An accumulation of mean temperature figures to aid estimating when grasses might come into flower and produce seed heads and for the application of a plant growth regulator, if deemed appropriate. GDD can also be used for estimating different stages of pest development to help in determining suitable control methods. The maximum and minimum daily temperatures are summed and then divided by two, with the base temperature being deducted to produce the required figure.
Growing Season Length
The number of days where the average temperature is above 5C in the first period of the year of 6 continuous days up to when the average temperature drops below 5C for 6 continuous days, with the latter period only being counted after 1st July.
The long-term average UK growing season length, for the period 1961 – 1990 was 275.9 days, compared with 298.4 days for the period 1991 – 2020.