USDA Hardiness Zone 7a
Frost Dates for 08830 — Iselin, New Jersey
NOAA 1991–2020 normals from Plainfield, NJ (90 ft), 5 miles northwest.
Updated
In Iselin, the last spring frost (32°F) is around April 11 in half of years and has passed by April 27 in nine years out of ten. The first fall frost comes around October 28, as early as October 13 one year in ten, leaving a typical freeze-free season of 198 days (NOAA, Plainfield, NJ).
- Last spring frost
- April 11
- First fall frost
- October 28
- Growing season
- 198 days
- Hardiness zone
- 7a
50% probability
50% probability
freeze-free, 50%
0 to 5°F (-17.8 to -15.0°C) coldest night
- First snow
- December 27
- Last snow
- March 9
- Winters with snow
- 100%
- Snow per year
- 26.3"
median, 1991–2020
median, 1991–2020
21 of 21 observed
NOAA normal
Frost risk by date in Iselin
Half of springs at Plainfield, NJ see their last 32°F night by April 11; only one in ten is past it by March 31, and one in ten still has one after April 27. Planting tender crops after April 18 leaves a 30% risk of a frost on them, after April 21 20%, and after April 27 10%. The 16 days between the even-odds date and the one-in-ten date is narrower than at 38% of the 56 New Jersey stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 28 in half of years, as early as October 13 one year in ten, and holds off past November 10 one year in ten. A hard freeze of 28°F follows 10 days later, around November 7; in spring the one-in-ten date for 28°F is April 11, 16 days before the 32°F one. The freeze-free season lasts 198 days in a typical year, longer than at 61% of the 56 New Jersey stations; it reaches 218 days one year in ten and falls short of 176 one year in ten. On average 103 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 16 days longer, to about April 27, and return around October 17. Severe cold of 16°F or below comes every winter, usually between December 22 and February 27.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 12 | Apr 17 | Apr 21 | Apr 24 | Apr 27 | Apr 30 | May 2 | May 7 | May 13 |
| 32°F | Mar 31 | Apr 3 | Apr 6 | Apr 9 | Apr 11 | Apr 15 | Apr 18 | Apr 21 | Apr 27 |
| 28°F | Mar 16 | Mar 21 | Mar 26 | Mar 30 | Mar 31 | Apr 2 | Apr 4 | Apr 7 | Apr 11 |
| 24°F | Mar 4 | Mar 9 | Mar 13 | Mar 17 | Mar 20 | Mar 23 | Mar 26 | Mar 30 | Apr 1 |
| 20°F | Feb 21 | Feb 28 | Mar 3 | Mar 6 | Mar 9 | Mar 13 | Mar 15 | Mar 20 | Mar 24 |
| 16°F | Feb 2 | Feb 10 | Feb 17 | Feb 23 | Feb 27 | Mar 2 | Mar 6 | Mar 10 | Mar 16 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 3 | Oct 8 | Oct 11 | Oct 14 | Oct 17 | Oct 19 | Oct 22 | Oct 26 | Nov 1 |
| 32°F | Oct 13 | Oct 18 | Oct 22 | Oct 25 | Oct 28 | Oct 31 | Nov 2 | Nov 5 | Nov 10 |
| 28°F | Oct 24 | Oct 30 | Nov 1 | Nov 4 | Nov 7 | Nov 10 | Nov 13 | Nov 17 | Nov 23 |
| 24°F | Nov 5 | Nov 9 | Nov 12 | Nov 16 | Nov 20 | Nov 24 | Nov 29 | Dec 3 | Dec 8 |
| 20°F | Nov 14 | Nov 20 | Nov 27 | Dec 1 | Dec 4 | Dec 9 | Dec 15 | Dec 20 | Dec 28 |
| 16°F | Nov 30 | Dec 5 | Dec 12 | Dec 18 | Dec 22 | Dec 27 | Jan 1 | Jan 5 | Jan 14 |
Freeze probabilities 1991–2020 at Plainfield, NJ, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 08830 →Compare Iselin with another place →
Weather by month in Iselin
July is the warmest month at Plainfield, NJ, averaging 88°F by day and 66°F at night; January is the coldest at 41°F and 24°F. A freezing night is all but certain in every month from November to March (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 88% of years.
Warmth for growing adds up to 3,713 growing degree days a year (base 50°F), more than at 75% of the 56 New Jersey stations. 34% of them (1,268) have built up by the end of June, and July adds the most, 838. Precipitation totals 48.7 inches a year, most in July (5.3") and least in February (3.1"); May to September bring 45% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 41 | 24 | 3.8 | 100% | 25 | 4 |
| Feb | 44 | 26 | 3.1 | 100% | 22 | 3 |
| Mar | 53 | 32 | 4.3 | 100% | 16 | 35 |
| Apr | 66 | 42 | 3.6 | 88% | 4 | 160 |
| May | 75 | 51 | 4.0 | 5% | <1 | 407 |
| Jun | 84 | 60 | 4.3 | 0% | 0 | 660 |
| Jul | 88 | 66 | 5.3 | 0% | 0 | 838 |
| Aug | 86 | 64 | 4.0 | 0% | 0 | 775 |
| Sep | 79 | 58 | 4.3 | 0% | 0 | 554 |
| Oct | 66 | 46 | 4.3 | 61% | 2 | 215 |
| Nov | 56 | 36 | 3.5 | 99% | 12 | 52 |
| Dec | 46 | 29 | 4.2 | 100% | 22 | 11 |
Monthly normals 1991–2020 at Plainfield, NJ (90 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Cranford, NJ, 7 miles north of Iselin, has the same 50% last-frost date, a first frost 3 days later (October 31), a season 4 days longer.
When it snows in Iselin, New Jersey
The first measurable snow (0.1 inch or more) in Iselin usually arrives around December 27, and the last of the season around March 9. Those are the middle dates across the winters of 1991–2020 at Cranford, NJ, 6.6 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 33 days after the last snow.
Planting calendar for 08830
| When | What to do |
|---|---|
| January 31 – February 14 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 14 – February 28 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 14 – March 28 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 11 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by August 5 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 14 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 28 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 08830 is 5 miles from Plainfield, NJ, which stands at 90 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 22 other ZIP codes share the station; its figures are presented in full for 08854 (Piscataway). The 2023 USDA Plant Hardiness Zone Map lists ZIP 08830 in zone 7a, the band where the coldest night of the year averaged 0 to 5°F (-17.8 to -15.0°C) over 1991–2020; a zone describes winter lows, not frost dates.
Frost dates across New Jersey →
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.