The Cooperative State Research, Education, and Extension Service at New Mexico State University recommends a mix of not more than  clay, not less than  sand, and never more than  silt.
ðə koʊˈɑːpɚɹətˌɪv stˈeɪt ɹᵻsˈɜːtʃ, ˌɛdʒuːkˈeɪʃən, ænd ɛkstˈɛnʃən sˈɜːvɪs æt nˈuː mˈɛksɪkˌoʊ stˈeɪt jˌuːnɪvˈɜːsᵻɾi ɹˌɛkəmˈɛndz ɐ mˈɪks ʌv nˌɑːt mˈoːɹ ðɐn klˈeɪ, nˌɑːt lˈɛs ðɐn sˈænd, ænd nˈɛvɚ mˈoːɹ ðɐn sˈɪlt.