Stability criteria Λ(r) + q − 1 > 0 for growing dust grains when already grown dust grains (left) and vertical settling (right) are present. Colour schemes are the same as for Fig. 1 (left): black: all models; red: a_max = 1 μm–10 μm, blue; a_max = 100 μm–10 mm and for Fig. 5 (right): no settling (black); α_SS ≥ 10^-2 (low settling, red); or α_SS < 10^-2 (strong settling, blue). H(100 AU) is defined here as where T(r) is the dust midplane temperature, r = 100 AU, M_star = 1 M_⊙, and μ = 2.3 is the mean molecular weight.