When it is sown (hotan sparēi). Second aorist passive subjunctive of speirō. Alone in Mark and repeated in Mar 4:32.
Less than all the seeds (mikroteron pantōn tōn spermatōn). Comparative adjective with the ablative case after it. Hyperbole, of course, but clearly meaning that from a very small seed a large plant grows, the gradual pervasive expansive power of the kingdom of God.