Gardening in New Hampshire

Hardiness zones in New Hampshire

New Hampshire spans USDA hardiness zones 4a to 6b. This number comes from the average annual minimum winter temperature in your area. A low zone number like 4a means harder winter cold, while a higher zone like 6b means milder winter lows. The zone range across the state runs from 4a in the coldest spots to 6b in the mildest ones. This single number says nothing about summer heat, rainfall, humidity, or your soil type. Two towns in the same zone can still have very different summers. Use your zone to pick plants rated to survive your winter low, then check frost dates and local conditions for everything else. With 55 weather stations feeding this data, the zone map reflects real variation across the state rather than one single average.

• Zone 4a
• Zone 4b
• Zone 5a
• Zone 5b
• Zone 6a
• Zone 6b

Frost dates

Your first fall frost can arrive as early as September 18. In colder parts of the state it may wait until October 19. Your last spring frost can hit as early as April 21 in milder areas. In colder spots it can linger until May 31. That is more than a month of spread in each direction. A frost date from one town does not apply to the next. Check your local station rather than a single statewide date. Plan tender seedlings and transplants around your own last frost date. Wait until after that date to set out warm season crops like tomatoes and peppers. In fall, watch for your first frost date so you know when to bring in houseplants. These dates mark the average risk of frost, not a guarantee. A light frost can still arrive earlier or later than expected in any single year.

Climate

This state's climate data spans a wide range, drawn from 55 weather stations across New Hampshire. Hardiness zones run from 4a to 6b, a wide span for one state. The length of the growing season tells a similar story. Some areas get as many as 180 frost-free days each year, while others get as few as 66. That is a gap of well over 100 days between the shortest and longest growing seasons recorded. Frost timing shows the same spread. The first fall frost can land anywhere between September 18 and October 19 depending on location. The last spring frost ranges from April 21 to May 31. Because these figures are drawn from 55 separate stations, the ranges reflect real local differences rather than one average for the whole state. None of this data describes summer heat, humidity, or rainfall. Pair your zone and frost dates with what you already know about your own site before you plan a garden.

Season length

How long your growing season lasts depends on where in New Hampshire you live. The data behind this page shows a range from 66 to 180 frost-free days a year across the state's stations. That means some gardeners get nearly six months without frost, while others get just over two. Check your own last spring frost date and first fall frost date to estimate your actual growing window. Short-season gardeners should favor quick-maturing crops and consider starting seeds indoors to make the most of the days they have. Long-season gardeners have more room to grow crops that need extra time to mature.