I think the general rule of thumb is Mother's Day, middle of May. There's probably a frost map if you Google it.

CITY / SPRING / FALL
Atlantic City 5/15 9/28
Hammonton 4/25 10/3
Jersey City 4/18 10/19
Millville 4/29 10/10
Newark 4/15 10/26
Newton 5/24 9/19
Shiloh 4/29 10/12
Trenton 4/15 10/23

Average last frost date can be deceiving because you can still get a frost after that date. For example, I'm close to Newark but April 15 is way too early to plant Impatiens or Tomatoes. My local garden center posts the "safe" date as May 15. I recommend checking with a good, local nursery for the date in your area.

It might be worth putting out extra or easily replaceable plants early for a head start. Last year I don't remember any frost in April - nothing floating row cover wouldn't have dealt with.

Lisa

Proximity to cities, water, local topography, your house, and individual microclimates play a major role. Temps during strong radiational cooling can vary by 10 degrees or more over a short distance. Over a period of years, you'll get a feel for your local temperatures and when frost is imminent. You'll get a different feeling when your newly planted impatiens turned to mush!

Steve, that is so true. There is a microclimate in my small veggie garden situated in between the house and deck--southern exposure. However, my tomato plants go in first on or later than 5/10; and the warmer plants such as pepper, eggplants, green beans follow toward the end of the month. But, there again, it is a matter of common sense if we happen to have colder evenings, certainly one should refrain from setting out plants too early depending upon the temps in your particular setting.

Vicki