When to Plant Lettuce in Portsmouth, NH
Published: April 21, 2026
Lettuce Planting Dates for Portsmouth, NH
| Start seeds indoors | March 18–25 |
| Last frost (average) | April 15 |
| Transplant outdoors | March 18–28 |
| Direct sow outdoors | March 4–14 |
| Minimum soil temperature | 40°F |
| Expect first harvest | April 17 – May 17 |
| Fall crop planting | September 3–13 |
| Fall crop harvest | October 3 |
| First fall frost (average) | October 15 |
Best Lettuce Varieties for Portsmouth, NH
For Zone 5a Portsmouth, the best-performing lettuce varieties are Arctic King, Winter Marvel, and Tom Thumb — all short-season varieties chosen for cool-climate reliability. These varieties are typically stocked by local nurseries and are the safest bets for gardeners new to lettuce in Portsmouth.
Growing Lettuce in Portsmouth
Portsmouth sits in Zone 5a, with an average last frost of April 15 and first fall frost around October 15 — giving a 183-day frost-free growing season. Cool-season crops like lettuce benefit from Portsmouth's cooler spring and fall windows, when temperatures stay in the 55–75°F sweet spot that produces the best flavor and least bolting.
Portsmouth's cooler summers are close to ideal for lettuce. The same conditions that limit tomato and pepper yields benefit cool-season crops — slower bolting, sweeter flavor, and longer harvest windows. The fall lettuce crop in Portsmouth is often more productive than the spring crop.
Portsmouth's well-draining loam soils are among the best for lettuce growing — focus on annual organic matter additions (2 to 3 inches of compost) and consistent moisture during drier months. Water lettuce at 1 inches per week; loam holds moisture evenly without the drought-crack cycle of heavy clay or the rapid-drain losses of pure sand.
Lettuce Calendar for Portsmouth
| Month | Task |
|---|---|
| March | Start seeds indoors under grow lights |
| April | Last frost — harden off seedlings outdoors |
| March | Transplant outdoors into warm soil |
| April | Expect first harvest window to open |
| September | Start fall crop — transplants or direct sow |
| October | First fall frost — harvest remaining, end of outdoor season |
Lettuce Tips for Portsmouth Gardeners
- •Direct sow very shallowly — lettuce seeds need light to germinate; cover with just 1/8 inch of soil.
- •Cut outer leaves 1 inch above the crown for "cut-and-come-again" harvests lasting weeks.
- •Fall plantings in Portsmouth often out-produce spring plantings — cooler temperatures slow bolting and concentrate flavor. Light frost can actually improve the taste of lettuce.
Common Lettuce Pests in Portsmouth
- •Aphids — peaks July in Zone 5a (active June–August); clusters on leaf undersides; blast with a strong water spray or apply neem oil.
- •Slugs — peaks July in Zone 5a (active June–August); active at night; set beer traps or use iron phosphate pellets.
- •Cutworm — peaks July in Zone 5a (active June–August); cuts seedlings at soil line; protect stems with paper collars or diatomaceous earth.
Check plants every 2–3 days during peak season — early intervention prevents most infestations from becoming serious.
What to Plant with Lettuce in Portsmouth
In Portsmouth's cold climate, Carrot and Radish are the most beneficial plants to grow alongside lettuce. Carrot shares root-zone space without competing because carrot roots run deeper than most companions. Keep lettuce away from Fennel — it releases root chemicals that inhibit growth of most neighbors. In short-season gardens, interplanting companions at transplant time maximizes each bed's productive weeks.
Frequently Asked Questions
When should I plant lettuce in Portsmouth, NH?
In Portsmouth (Zone 5a), start lettuce seeds indoors around March 18–25 and transplant outdoors around March 18–28. The city's average last frost of April 15 is the anchor date — count 4 weeks back for seed starting and 4 weeks back for transplanting.
What zone is Portsmouth, NH for lettuce growing?
Portsmouth is USDA Zone 5a. For lettuce, this means a frost-free growing season of roughly 26 weeks running from April 15 to October 15. Cool-season crops like lettuce thrive in this zone with both spring and fall planting windows available.
When is lettuce harvest season in Portsmouth?
Expect the first lettuce harvest in Portsmouth around April 17, with harvest continuing through May 17. This is based on 30–60 days from transplant or direct sow. A fall crop planted September 3–13 adds a second harvest around October 3.
How long does it take to grow lettuce in Portsmouth, NH?
From transplant or direct sow to first harvest, lettuce takes 30–60 days in Portsmouth's climate. Based on a typical planting date of March 18–28, expect your first harvest around April 17. Portsmouth's cooler Zone 5a climate often lands at the slower end of this range — cooler nights slow fruit development.
What soil does lettuce need in Portsmouth?
Portsmouth's loam soil is near-ideal for lettuce. Work in 2–3 inches of compost before planting to boost organic matter and nutrient content. Minimal amendment is needed beyond that — loam holds moisture evenly without the drought-crack cycle of clay or the nutrient-loss issues of sandy soil.