USDA Hardiness Zone 5b
Frost Dates for 03809 — Alton, New Hampshire
Averages from Lakeport 2, Nh US, the nearest reporting station, 13 miles away.
Plant tender crops after April 30, and expect the first autumn freeze around October 18. That leaves about 170 frost-free days.
- Last spring frost
- April 30
- First fall frost
- October 18
- Growing season
- 170 days
- Hardiness zone
- 5b
50% probability
50% probability
frost-free
-15 to -10°F annual low
- First snow
- December 2
- Last snow
- March 31
- Winters with snow
- 100%
- Snow per year
- 61.9"
median, 1991–2020
median, 1991–2020
30 of 30 observed
NOAA normal
When it snows in Alton, New Hampshire
The first measurable snow (0.1 inch or more) in Alton, New Hampshire usually arrives around December 2, and the last of the season around March 31. Those are the middle dates across the winters of 1991–2020 at Lakeport 2, Nh US: half of years saw snow earlier, half later. Every one of those winters saw snow.
For a gardener, snow matters less than frost: a light snow on frozen ground changes nothing, while a hard frost on an unprotected bed ends the season. Use the frost dates above for planting and the snow dates for getting hoses drained, mulch down and tender pots indoors.
Planting calendar for 03809
| When | What to do |
|---|---|
| February 19 – March 5 | Start peppers and aubergines indoors They need eight to ten weeks under lights before they can go out. |
| March 5 – March 19 | Start tomatoes indoors Six to eight weeks gives a transplant big enough to set fruit early. |
| April 2 – April 16 | Sow peas, spinach, lettuce, radish outdoors These tolerate light frost and prefer to germinate in cool soil. |
| April 30 onward | Transplant tomatoes, peppers, basil, squash, cucumbers The average last freeze has passed — still watch the actual forecast. |
| by July 26 | Sow the autumn crop of carrots, beets and brassicas They need about twelve weeks to size up before growth stops. |
| by October 4 | Harvest tender crops, or be ready to cover them A first freeze two weeks early is well within normal variation. |
| October 18 onward | Plant garlic, mulch beds, lift tender bulbs Garlic wants a cold spell; bare soil loses structure over winter. |
What these dates mean
Wait until after April 30 to put tender plants — tomatoes, peppers, basil, squash — in the ground. That is the date by which half of years in Alton, New Hampshire are past their last freeze. Harvest before October 18, which leaves roughly 170 frost-free days.
ZIP 03809 sits in USDA hardiness zone 5b, meaning the average coldest night of the year falls between -15 to -10°F. Zone decides what survives the winter; frost dates decide when to plant each spring. They are different questions, and a plant can pass one and fail the other.
These are thirty-year NOAA averages for 1991–2020, not a forecast. Any individual year can frost two to three weeks either side of these dates, so check the actual forecast before planting out.