We investigated different concentrations of auxins (IAA, IBA, NAA), the strength of the MS medium, sucrose and ammonium/nitrate contents, initial medium pH, and inoculum size to determine their effects on biomass increase and the accumulation of total phenols and flavonoids in adventitious roots of Echinacea angustifolia. These roots were cultured under darkness in shake flasks for 4 weeks. IBA proved the best auxin for inducing root proliferation. Root growth was inhibited when the initial pH was maintained below 5.0 or above 6.0. Nitrate, rather than ammonium, was more necessary for root growth and phenolics accumulations. Overall, biomass increased and total phenol and flavonoid contents were maximized under the following conditions: half-strength MS medium supplemented with $2mgL^{-1}$ IBA, 5% (w/v) sucrose, 5:25 (mM) ammonium/nitrate ratio, pH adjusted to 6.0 before autoclaving, and an inoculum size of $10gL^{-1}FW$. These results indicate that the type of in vitro environment strongly affects growth and the accumulation of phenolics from adventitious root cultures of E. angustifolia. Such optimization is beneficial to large-scale production of biomass and secondary metabolites in that species.