A mixture of rock dust (RD) and vermicompost (VC) provides a nutrient-rich and microbiologically-active natural growing medium for plants. However, their complementary effect is understudied. A greenhouse experiment was performed to determine the combined effect of RD and VC on dahlia (Dahlia pinnata `Cobequid Celestial Star') plant growth, flower production and tuberous root yield. The experimental treatments were: Promix BXTM alone (control), 20 g RD + 22.5 g VC, 20 g RD + 45 g VC, 40 g RD + 22.5 g VC, 20 g RD alone and 45 g VC alone. The 20 g RD + 45 g VC and the 45 g VC alone significantly (P<0.01) increased anthocyanin contents of the dahlia plants relative to the control. Chlorophyll content and plant height did not vary statistically (P>0.05), but were slightly higher in the 20 g RD+45 g VC treated plants. However, photosynthetic activities were significantly (P<0.05) highest in the 45 g VC alone treated plants. Tuberous root diameter was significantly (P<0.01) highest in the 20 g RD alone and the 45 g VC alone treatments, and the least in the 20 g RD+45 g VC treatment. Indices of photosynthetic efficiency were consistently and significantly (P<0.05) highest in the 45 g VC alone but were significantly (P<0.05) reduced by the control and the 40 g RD + 22.5 g VC. Flower production and flower bud opening were significantly (P<0.05) reduced by the control and the 20 g RD + 22.5 g VC but were significantly (P<0.05) increased by treatments 20 g RD + 45 g VC and the 45 g VC alone. Thus, the present study suggested that application of vermicompost with (20 g RD + 45 g VC) or without (45 g VC alone) rock dust improved plant growth and flower production. The effectiveness of vermicompost can be boosted by rock dust. Future studies should consider effects of moisture content and mycorrhizal activities.
