Depends on the plant. Those you mention are all well able to take a frost but I don't know about many days of deep freeze. How cold does it get where you are and for how long?

All of your suggestions can come true. As floral_uk said it depends on the plant and even within the same species it will depend on the age and size of the plant. Some will weather the break with no ill effects, others with suffer some damage, some will lose this new foliage but grow again in spring, and unfortunately some may die. Good luck with yours.

Temperatures are very unpredictable here. Even though these days nightime temperatures never really went down 25 degrees, last year in January it stayed under 10 degrees for a while. The coldest it gets here is 0 degrees. And that’s rare. Usually frost isn’t over until late March/beginning April.

Climate chaos is the new normal and we're all in uncharted territory.

I am in NJ too (Zone 7), the grass is greening up and the forsythia is in bloom (my acquaintances in "ski country" NJ, tell me it looks like March or April out on the sloops); while in previous, recent winters we were in the grip of multiple, polar vortices as the arctic fronts penetrated to Cuba. Local climate has become extremely erratic in terms of winter temperatures (subarctic to subtropical) and annual precipitation (severe drought to tropical deluges..., in the "winter") It has got to be stressful to the native and non-native plants, but we are not alone in experience of bizarre weather/climate confusion! Hang on, gonna be a bump ride!

Veering off topic, but I got the second set of seeds today, two species that required vernalization. The forecast for the next two days is mid 60s and there's only one day that it dips below freezing in the 15 day forecast. I worry that my seeds won't sprout this year (lol). I had some that I planted in late January last year that didn't get enough to sprout (hoping for them this spring).

Dbarron, refrigerator stratification?

Heruga, my first strategy is prevention to the best of my ability. Plants in my zone that want to open buds too early get planted where they are likely to be shaded by sun angle for longer in winter and early spring, so on the north side of a short building or evergreen, for instance. Colder soil delays budding development IME. Mulch also helps shelter plant roots from temperature swings.

Here, many plants will start buds swelling (or like daffodils will put up leaves just to a certain point) and then stop until conditions are right over a longer stretch of time. Many buds and bulb leaves are quite frost and cold hardy, though not all. I may lose flowers some years if they open before a hard frost. IME woody plants that have leafed out and been frozen back will releaf out, and because it takes a while for new buds to develop, I have never had this happen more than once per season on woody plants. I have had absolute cold kill woody plants, but have never had new leaves being frozen kill one.

For perennials, most are budding out at ground level and so stay cold/@soil temperature here, which keeps them in a suspended state. Air temperatures change much faster than soil temps. However, there aren’t going to be any hard and fast answers, and only experience will answer the questions in your specific garden with your specific plants.

For the sake of your long term stress levels, take a deep breath, relax, and wait to see what happens since there is really nothing you can do at this point to change things for this year. Try starting a garden journal (computerized is nice since you can add digital photos, etc.) where you keep track of daily high and low temperatures, where the sun is as the seasons roll around the year, and what you observe In your plants. That will be the start of a long term record that will help you answer these questions for your particular site.

As Ken always says, they are plants, not children. They can be replaced. If having borderline hardy plants is too stressful, plant ones a zone hardier. Gardening should be a pleasure.

I grow and hybridize some of the Asiatic Mayapples and have lost all above ground parts on occasion from late frosts. Generally this sets the plant back for several years. Have never lost a hardy bulbous plant due to frost, and few others. Cold/dry wind is a very damaging problem for me, more than frost. I'm in Pa, just adross the river from OP area and in nominally 7a zone but on a steep slope with open area above so have so-called 'frost drainage' as the chilled air drains down to the valley below.

Babs, my fridge runneth over (with food items). Stratification for me is only outdoors.

No room for a ziplock, damp soil or paper towel and seeds?

I'm an unorganized slob, it would be lost/forgotten/rotted before I found it again. Seriously plants are safer outside ;)

zone is basically only low winter temp

(This isn't the case for Canadian hardiness zones).

Rouge, can you explain further? I see that your zones do take into consideration other climatic factors but how are they reflected in the hardiness zones? How does your hardiness zone 6 compensate for rainfall or summer heat, for example, and how is that reflected in the zone designation?

Sorry for the delay in responding 'gg'.

And I quote from a government of Canada website:

The Canadian index is based on 7 climate variables, not just minimum temperature.

The FORMULA for Canadian hardiness zones

Now there are 8 variables since elevation has also been added.

http://sis.agr.gc.ca/cansis/nsdb/climate/hardiness/index.html

and by municipality where you can select the nearest town or city.

http://www.planthardiness.gc.ca/index.pl?m=22&lang=en

I'm still not sure how all those variables can be accurately reflected in only 8 zones!! Even Sunset, which takes into consideration all of these same variables, has 24 zones for just the west coast!

Wow! Thanks for the information rouge21_gw and peren.all! I just found out that I am actually in Zone 8a and not 7a as I had always thought! I now wonder why my Dahlias didn't survive their first year.

I am actually in Zone 8a and not 7a

Kind of scary though eh?

Yes, it brings up the whole question on global warming!