Timothy is the primary forage grass seed crop in Norway, and thus effective control of dicot weeds and lodging management are critical steps in maximizing timothy seed yield and meeting seed purity standards. Optimal timing of gibberellic acid–inhibiting plant growth regulators (PGRs), such as chlormequat chloride (CCC) and trinexapac-ethyl (TE), often coincides with spring herbicide applications, raising concerns about crop safety and herbicide efficacy when products are tank-mixed. Field experiments were conducted in 2022 and 2023 at two locations in Norway to evaluate the effect of mixing PGRs with commonly used herbicides on timothy lodging, seed yield, and seed quality. Plant growth regulators (1,500 g ai ha⁻1 CCC and 150 g ai ha⁻1 TE) were applied either separately (herbicides at BBCH stage 25; PGRs at BBCH stage 35) or tank-mixed (at BBCH stages 30 to 35) with one of three herbicide combinations: fluroxypyr + florasulam, florasulam + diflufenican, or aminopyralid + 2,4-D + florasulam. Seed yield was affected by PGR treatments (P ≤ 0.05) but not by herbicide treatments. Plant height and lodging were reduced more with TE than with CCC; however, relative yield responses varied with timothy stand age. Tank mixing both products did not reduce seed yield or herbicide efficacy. Crop injury from tank mixtures was minimal and temporary, and no reductions in final seed germination were observed. Tank-mixing CCC and TE PGRs with herbicides maintained optimal seed yield and quality, offering operational flexibility for timothy seed producers.