Iowa Code § 446.25: Sale adjourned.

When all the parcels advertised for sale have been offered and parcels remain unsold for want of bidders, the county treasurer shall adjourn the sale to some day not exceeding two months from adjournment, due notice of which day shall be given at the time of adjournment, and by keeping the notice posted in a conspicuous place in the treasurer’s office. Further notice is not necessary. On the day fixed by the adjournment, the same proceedings shall occur as in the first instance. Further adjournments shall be made, not exceeding intervals of two months, and the sales continue until the next regular annual sale or until all the parcels are sold.