citron
[ si-truhn ]
noun
a pale-yellow fruit resembling the lemon but larger and with thicker rind, borne by a small tree or large bush, Citrus medica, allied to the lemon and lime.
Basically growing in an inorganic medium, with a water reservoir that wicks water through the medium... usually LECA is most common. (Lightweight Expanded Clay Aggregate).
__________________ Caveat: Everything suggested is based on my environment and culture. Please adjust accordingly.