When to Plant Broccoli in Portsmouth, NH
Published: April 21, 2026
Broccoli Planting Dates for Portsmouth, NH
| Start seeds indoors | March 4–11 |
| Last frost (average) | April 15 |
| Transplant outdoors | March 18–28 |
| Direct sow outdoors | March 18–28 |
| Minimum soil temperature | 40°F |
| Expect first harvest | May 17 – June 6 |
| Fall crop planting | August 6–16 |
| Fall crop harvest | October 5 |
| First fall frost (average) | October 15 |
Best Broccoli Varieties for Portsmouth, NH
For Zone 5a Portsmouth, the best-performing broccoli varieties are Arcadia, Belstar, and Diplomat — 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 broccoli in Portsmouth.
Growing Broccoli 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 broccoli 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 broccoli. The same conditions that limit tomato and pepper yields benefit cool-season crops — slower bolting, sweeter flavor, and longer harvest windows. The fall broccoli crop in Portsmouth is often more productive than the spring crop.
Portsmouth's well-draining loam soils are among the best for broccoli growing — focus on annual organic matter additions (2 to 3 inches of compost) and consistent moisture during drier months. Water broccoli at 1.5 inches per week; loam holds moisture evenly without the drought-crack cycle of heavy clay or the rapid-drain losses of pure sand.
Broccoli 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 |
| May | Expect first harvest window to open |
| August | Start fall crop — transplants or direct sow |
| October | First fall frost — harvest remaining, end of outdoor season |
Broccoli Tips for Portsmouth Gardeners
- •For spring: start indoors 6 weeks before last frost and transplant outdoors 4 weeks before last frost.
- •For fall: start indoors in summer — count 10 weeks back from your first fall frost date.
- •Fall plantings in Portsmouth often out-produce spring plantings — cooler temperatures slow bolting and concentrate flavor. Light frost can actually improve the taste of broccoli.
Common Broccoli Pests in Portsmouth
- •Cabbage Worm — peaks July in Zone 5a (active June–August); green caterpillars on brassicas; apply Bt spray or use row covers.
- •Cabbage Looper — peaks July in Zone 5a (active June–August); loop-walking green caterpillars; Bt spray works well.
- •Aphids — peaks July in Zone 5a (active June–August); clusters on leaf undersides; blast with a strong water spray or apply neem oil.
Check plants every 2–3 days during peak season — early intervention prevents most infestations from becoming serious.
What to Plant with Broccoli in Portsmouth
In Portsmouth's cold climate, Onion and Garlic are the most beneficial plants to grow alongside broccoli. Onion deters carrot fly, aphids, and several root-zone pests through sulfur compounds. Keep broccoli away from Tomato — it competes for nutrients or shares pest pressure. In short-season gardens, interplanting companions at transplant time maximizes each bed's productive weeks.
Frequently Asked Questions
When should I plant broccoli in Portsmouth, NH?
In Portsmouth (Zone 5a), start broccoli seeds indoors around March 4–11 and transplant outdoors around March 18–28. The city's average last frost of April 15 is the anchor date — count 6 weeks back for seed starting and 4 weeks back for transplanting.
What zone is Portsmouth, NH for broccoli growing?
Portsmouth is USDA Zone 5a. For broccoli, this means a frost-free growing season of roughly 26 weeks running from April 15 to October 15. Cool-season crops like broccoli thrive in this zone with both spring and fall planting windows available.
When is broccoli harvest season in Portsmouth?
Expect the first broccoli harvest in Portsmouth around May 17, with harvest continuing through June 6. This is based on 60–80 days from transplant or direct sow. A fall crop planted August 6–16 adds a second harvest around October 5.
How long does it take to grow broccoli in Portsmouth, NH?
From transplant or direct sow to first harvest, broccoli takes 60–80 days in Portsmouth's climate. Based on a typical planting date of March 18–28, expect your first harvest around May 17. Portsmouth's cooler Zone 5a climate often lands at the slower end of this range — cooler nights slow fruit development.
What soil does broccoli need in Portsmouth?
Portsmouth's loam soil is near-ideal for broccoli. 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.