Microgreens are short-cycle crops whose establishment and productivity are strongly influenced by the growing substrate. Repurposing used tea powder as a growing medium for microgreens, is one of the approaches in addressing both the need for sustainable substrates and waste management. The present study evaluated the growth performance of Amaranthus tricolor (red amaranth) and Brassica juncea (mustard) microgreens cultivated using spent tea powder (TP), cocopeat (CP), and a 1:1 combination of cocopeat and tea powder (CP + TP). Germination was assessed using cotton, TP, CP and CP + TP. Shoot and root growth, fresh weight, dry weight and moisture content were evaluated in microgreens cultivated on CP, TP and CP + TP. Germination of A. tricolor was highest on cotton and TP (100.00 ± 0.00%), whereas B. juncea showed maximum germination on CP + TP (93.33 ± 3.33%). TP produced the highest shoot length in both A. tricolor (3.97 ± 0.15 cm) and B. juncea (8.37 ± 1.63 cm). The longest root in B. juncea was recorded on CP + TP (3.00 ± 1.32 cm). TP also produced the greatest fresh and dry biomass in both species. Moisture content was highest in TP-grown A. tricolor (89.10 ± 0.36%) and CP + TP-grown B. juncea (87.73 ± 0.44%). The results demonstrate that spent tea powder is a promising alternative growing substrate for microgreen production, particularly for enhancing shoot growth and biomass, while the CP + TP combination may be advantageous for root development in B. juncea.