When to Plant Collard Greens in Portsmouth, NH
Published: April 24, 2026
Collard Green Planting Dates for Portsmouth, NH
| Start seeds indoors | March 11–18 |
| Last frost (average) | April 15 |
| Transplant outdoors | March 25–April 4 |
| Direct sow outdoors | March 25–April 4 |
| Minimum soil temperature | 45°F |
| Expect first harvest | May 24 – June 8 |
| Fall crop planting | August 6–16 |
| Fall crop harvest | October 5 |
| First fall frost (average) | October 15 |
⚠ Direct sow or transplant collard greens 3–4 weeks before last frost. Extremely cold hardy — withstands temps to 15°F. Can be grown as a perennial in Zones 8+. Fall planting produces the best-flavored greens.
Best Collard Green Varieties for Portsmouth, NH
Consult a Portsmouth-area nursery or your state extension office for collard green varieties proven in Zone 5a.
Growing Collard Greens 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 collard green 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 collard green. The same conditions that limit tomato and pepper yields benefit cool-season crops — slower bolting, sweeter flavor, and longer harvest windows. The fall collard green crop in Portsmouth is often more productive than the spring crop.
Portsmouth's well-draining loam soils are among the best for collard green growing — focus on annual organic matter additions (2 to 3 inches of compost) and consistent moisture during drier months. Water collard green 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.
Collard Green 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 |
Collard Green Tips for Portsmouth Gardeners
- •Harvest outer leaves continuously once plants reach 10 inches — the central growing point produces for months.
- •In Zones 8+ collard greens often overwinter and produce for 2–3 years as a perennial.
- •Fall plantings in Portsmouth often out-produce spring plantings — cooler temperatures slow bolting and concentrate flavor. Light frost can actually improve the taste of collard green.
Common Collard Green Pests in Portsmouth
- •Cabbage Worm — peaks July in Zone 5a (active June–August); green caterpillars on brassicas; apply Bt spray or use row covers.
- •Aphid — peaks July in Zone 5a (active June–August); monitor closely during peak season and treat early.
- •Flea Beetle — peaks July in Zone 5a (active June–August); tiny black beetles that riddle leaves with holes; row covers protect seedlings.
Check plants every 2–3 days during peak season — early intervention prevents most infestations from becoming serious.
What to Plant with Collard Greens in Portsmouth
In Portsmouth's cold climate, Onion and Garlic are the most beneficial plants to grow alongside collard green. Onion deters carrot fly, aphids, and several root-zone pests through sulfur compounds. Keep collard green 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 collard green in Portsmouth, NH?
In Portsmouth (Zone 5a), start collard green seeds indoors around March 11–18 and transplant outdoors around March 25–April 4. The city's average last frost of April 15 is the anchor date — count 5 weeks back for seed starting and 3 weeks back for transplanting.
What zone is Portsmouth, NH for collard green growing?
Portsmouth is USDA Zone 5a. For collard green, this means a frost-free growing season of roughly 26 weeks running from April 15 to October 15. Cool-season crops like collard green thrive in this zone with both spring and fall planting windows available.
When is collard green harvest season in Portsmouth?
Expect the first collard green harvest in Portsmouth around May 24, with harvest continuing through June 8. This is based on 60–75 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 collard green in Portsmouth, NH?
From transplant or direct sow to first harvest, collard green takes 60–75 days in Portsmouth's climate. Based on a typical planting date of March 25–April 4, expect your first harvest around May 24. Portsmouth's cooler Zone 5a climate often lands at the slower end of this range — cooler nights slow fruit development.
What soil does collard green need in Portsmouth?
Portsmouth's loam soil is near-ideal for collard green. 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.