When the USDA updated the plant hardiness zone map last year (long overdue, but to be fair, it does rely on prior decades' worth of climate data), horticulturists weren't surprised that Bay-adjacent areas and southern Maryland wound-up as zone 8a. (It's functionally been zone 8a already for some time now. Not all areas of zone 7 moved into zone 8, though.) An NPR article about the updated map includes a tool (at the very end of the article) that lets you explore the map, switching views between the old and new maps for any given area so you can see how the zone delineations changed.

Since zone 8 has a slightly longer growing season than zone 7, you can essentially extend the seasons of sowing and harvest by a little bit. (Last frost in spring and first frost in autumn will be a little earlier/later, respectively, than for a zone cooler. Still, it wouldn't be much different than the timing between sowing veggie seed or putting transplants outside in your area versus, say, Frederick or Washington County, even without a map zone update.) Our Vegetable Planting Calendar is a guide based on central Maryland temperature trends, so each region of Maryland (one zone cooler in the west and one zone warmer in the east/southeast) can adjust those times by a week or two if needed.

Microclimate also plays a role, which we can't account for in a standardized calendar. Microclimate relates to small-scale differences in growing conditions (mainly temperature) based on influences like nearby house walls retaining or reflecting warmth, low points where cool air can sink, expanses of stone, paving, or concrete that absorb and radiate warmth, and so on. Therefore, a dwarf peach tree growing in one person's yard might have frost ruin flowers one night based on the tree's shelter (or lack thereof) from cold winds or "frost pockets," and the same tree in another yard in the same neighborhood might escape damage due to just a few degrees of protection from some warmth-retaining feature nearby, or being located on a hill where frost settles into low-lying areas instead. They're both in the same zone, but still can experience just enough difference in temperature to have an impact; the same would apply to vegetables.

All this is to say that any such calendar or planting guide is just an estimate and individual yard conditions can be taken into account to extend the growing season or protect plants from frost or other issues. Using floating row cover, for example, can be one way to give cool-season crops (kale, etc.) more of a zone 8 winter experience in a zone 7 garden. What the updated map isn't designed to take into account, as the article above points out, is fluke cold snaps (since it uses average winter temperature lows, not the most extreme low) and high summer heat that can stress species that prefer cooler conditions.

Miri

You're welcome.