Exceptionally easy are Dietes bicolor , the African iris that sports yellow flowers with maroon-brown splotches, and D. vegata , the butterfly iris with blue and white blooms. These grow from corms. It would not surprise me if the irises in your mother's garden are bearded. These have the reputation of being difficult here. However, there are local gardeners who successfully grow bearded irises, but these must be varieties that will tolerate our long, hot summers and mild, wet winters.
Bearded irises have the caterpillarlike adornment on each fall, the outer, petal-like sepal.
Bearded types can be planted July into October. Plant the rhizomes in a sunny bed, just below the surface of organically enriched, well-draining soil. Water until growth begins but do not overwater. Keep the soil moist during the flowering period, usually late March into April, but when blooms stop, do not water as frequently and only water lightly in summer. The plants appear healthy until you look closely.