International Phenological Gardens of Europe - IPG
The IPG network
https://www.agrar.hu-berlin.de/de/institut/departments/dntw/agrarmet/phenology
was founded in 1959 by F. Schnelle and E. Volkert within the framework of an IPG working group.
The objective of the IPGs is the large-scale comparison of climate and weather influences on the growth of plants.
For this purpose, stages of development (phases) such as, for example, the beginning of the unfolding of leaves, beginning of flowering, fruit ripeness, leaf colouring, leaf fall on trees and bushes, are compared at climatically dissimilar sites across state boundaries.
All plants of a species are homozygous, i.e. they are descended from the same mother plant and were propagated vegetatively.
(source: http://www.dwd.de)