When to Plant Radishes in Portsmouth, NH
Published: April 24, 2026
Radish Planting Dates for Portsmouth, NH
| Start seeds indoors | Year-round |
| Last frost (average) | April 15 |
| Direct sow outdoors | March 11–21 |
| Minimum soil temperature | 40°F |
| Expect first harvest | April 2 – April 10 |
| Fall crop planting | September 10–20 |
| Fall crop harvest | October 2 |
| First fall frost (average) | October 15 |
⚠ Direct sow radishes 4–6 weeks before last frost — one of the fastest crops in the garden. Ready in as little as 22 days. Succession plant every 2 weeks for continuous harvest.
Best Radish Varieties for Portsmouth, NH
Consult a Portsmouth-area nursery or your state extension office for radish varieties proven in Zone 5a.
Growing Radishes 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 radish 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 radish. The same conditions that limit tomato and pepper yields benefit cool-season crops — slower bolting, sweeter flavor, and longer harvest windows. The fall radish crop in Portsmouth is often more productive than the spring crop.
Portsmouth's well-draining loam soils are among the best for radish growing — focus on annual organic matter additions (2 to 3 inches of compost) and consistent moisture during drier months. Water radish 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.
Radish Calendar for Portsmouth
| Month | Task |
|---|---|
| Year | Start seeds indoors under grow lights |
| April | Last frost — soil warming, prepare bed |
| March | Direct sow seeds 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 |
Radish Tips for Portsmouth Gardeners
- •Thin to 2-inch spacing when seedlings are an inch tall — crowded radishes produce small woody roots.
- •Succession plant every 10–14 days from early spring through late spring for continuous harvest.
- •Fall plantings in Portsmouth often out-produce spring plantings — cooler temperatures slow bolting and concentrate flavor. Light frost can actually improve the taste of radish.
Common Radish Pests in Portsmouth
- •Flea Beetle — peaks July in Zone 5a (active June–August); tiny black beetles that riddle leaves with holes; row covers protect seedlings.
- •Cabbage Root Maggot — peaks July in Zone 5a (active June–August); monitor closely during peak season and treat early.
- •Aphid — peaks July in Zone 5a (active June–August); monitor closely during peak season and treat early.
Check plants every 2–3 days during peak season — early intervention prevents most infestations from becoming serious.
What to Plant with Radishes in Portsmouth
In Portsmouth's cold climate, Lettuce and Carrot are the most beneficial plants to grow alongside radish. Lettuce improves nearby plant health and pest resistance. Keep radish away from Hyssop — 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 radish in Portsmouth, NH?
In Portsmouth (Zone 5a), direct sow radish around March 11–21. Soil must be at 40°F or warmer at 2-inch depth before sowing — cold soil rots the seeds.
What zone is Portsmouth, NH for radish growing?
Portsmouth is USDA Zone 5a. For radish, this means a frost-free growing season of roughly 26 weeks running from April 15 to October 15. Cool-season crops like radish thrive in this zone with both spring and fall planting windows available.
When is radish harvest season in Portsmouth?
Expect the first radish harvest in Portsmouth around April 2, with harvest continuing through April 10. This is based on 22–30 days from transplant or direct sow. A fall crop planted September 10–20 adds a second harvest around October 2.
How long does it take to grow radish in Portsmouth, NH?
From transplant or direct sow to first harvest, radish takes 22–30 days in Portsmouth's climate. Based on a typical planting date of March 11–21, expect your first harvest around April 2. Portsmouth's cooler Zone 5a climate often lands at the slower end of this range — cooler nights slow fruit development.
What soil does radish need in Portsmouth?
Portsmouth's loam soil is near-ideal for radish. 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.