This grower is sure of this plant identification.
The two larger plant clumps have been separated from a border of golden rod and both have some montbretia plants interspersed with them.
Solidago genus (Golden rod). This genus has about 100 species of woody-based summer and autumn flowering perennials. Some of the species are vigorous, coarse plants that tend to crowd out others in the border.
They are fully to frost-hardy plants, that will thrive in sun or shade. They will need a fertile, well-drained soil.
Cutting bed, naturaliser, wildflower/meadow