1. Go to the Spring Planting Calendar setup by Skippy’s Vegetable Garden
2. Enter the date 04/21/2009 as the “Last Spring Frost” date for Brooklyn.
3. Click the [Generate …] button.
4. See how late you already are!

The hardest part of figuring out when to start seeds or set out plants is knowing when the “last frost date” is for your location. NOAA has a set of charts of frost and freeze dates on their Web site, one for each state, with a set of date for each of their measuring stations. Here’s the explanation NOAA provides:

This product contains station freeze/frost probability tables for each state. Given are the dates of probable first and last occurrence … and the probability of experiencing a given temperature, or less … probabilities are given for three temperatures (36, 32, and 28 °f) at three probability levels (10, 50, and 90 percent).

The chart for New York state [PDF] lists four stations in New York City, including one on Avenue V in Brooklyn. Let’s look at the Spring-relevant subsection of the New York state table for NOAA’s Brooklyn station:

To get the “last frost date” for Brooklyn, I chose the most conservative – the safest – values: the highest of the three temperatures, 36F, and the 10% probability threshold. The date given is April 21. That means that there’s only a 10% chance that the temperature will drop to 36F or lower on or after April 21, so that’s the date I used for “Last Spring Frost” in the Spring Planting Calendar.

Links

Spring Planting CalendarSkippy’s Vegetable GardenNOAA charts of frost and freeze dates