We've seen numerous evergreens around the region develop winterburn, the name for the desiccation and browning of foliage that dried out during the winter, and it's not unusual for that type of damage to affect Nandina. Yes, cold temperatures combined with soil moisture unavailable to roots (either due to the ongoing drought or due to the fact that frozen water can't be absorbed by roots) was the cause. Winterburned foliage cannot recover and will be shed by the plant starting in spring, but if the stems themselves were not killed, new growth will eventually be produced to start the process of filling back in again. If stems also died back due to cold or drought, then an established Nandina can regrow easily from the roots.

If the shrub has been too badly damaged, consider replacing it, as Nandina is an invasive species in Maryland. Maryland recently updated a law that prohibits certain invasive plants from being sold, and Nandina was just added to that list (the ban will take effect in the next 1-2 years, so garden centers might still be selling it this year). While the law doesn't require that specimens of the banned plants that are already growing in landscapes be removed, we encourage gardeners to replace them (especially if you would otherwise want to replace them if they are damaged or struggling) with non-invasive and ideally native alternatives.

Miri