Summary The extended BBCH scale is a system for a uniform coding of phenologicaliy similar growth stages of all mono‐ and dicotyledonous plant species, based on the well known cereal code of Zadoks et al. (1974). The BBCH key is it decimal system, with 10 principal growth stages and up to 10 secondary ones, starting with seed germination, sprouting of perennials, progressing through leaf production and extension growth to flowering and senescence. Therefore, it can also be a suitable tool to define the growth stages of different weed species. To encourage further use of the BBCH scale in weed research, definitions of the codes have been more closely adapted to weeds. Possible problems are discussed and guidelines for correct use are given.

Following the introduction of the general BBCH scale, the specific BBCH scale for the upland cotton plant is presented which provides crop‐specific descriptions and detailed assessment instructions. The development process of the plant is described by periods (principal growth stages) and steps (secondary growth stages). A 2‐digit decimal code suitable for data processing in crop production experiments is assigned to each step of development.

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