When to Plant Vegetables in Portsmouth, NH
Portsmouth sits in USDA Zone 5a, a cold climate with a relatively short growing season. Frost can linger well into spring and return early in fall, so timing is everything. Start warm-season crops like tomatoes and peppers indoors 6–8 weeks before your last frost date and rely on cold frames and row covers to extend both ends of the season. Cool-season vegetables such as lettuce, spinach, peas, and kale are the backbone of a successful Portsmouth garden — they tolerate light frost and produce excellent harvests in spring and fall. Garlic planted in October overwinters beautifully in Zone 5a and is one of the most reliable crops you can grow.
Understanding Portsmouth's Growing Seasons
Portsmouth's Zone 5a climate gives you one main growing season — from last frost (April 15) to first frost (October 15). That's approximately 26 weeks to grow everything from transplant to harvest. Maximizing this window with succession planting, early indoor starts, and fall extension is the key to cold zone productivity.
Don't rush — planting warm-season crops before April 15 kills them. Use your local last frost date as your master planning date.
What to Plant This Month in Portsmouth
May
Direct Sow Outdoors
Bean, Corn, Zucchini, Cucumber, Radish, Beet
Transplant Outdoors
Tomato, Pepper, Eggplant, Basil
Harvest
Radish, Spinach, Lettuce
Tasks
- Transplant warm-season crops after last frost (May 15-30 for most zone 3-5 areas)
- Use wall-of-water protectors around tomatoes if planting before Memorial Day
- Direct sow beans, corn, squash, and cucumbers after soil reaches 60°F
- Succession plant lettuce and radish every 2 weeks
- Mulch around transplants to retain moisture and suppress weeds
- Monitor for cutworms around new transplants
Full 12-Month Planting Calendar for Portsmouth
| Month | Direct Sow | Transplant | Start Indoors | Harvest |
|---|---|---|---|---|
| Jan | — | — | Onion, Lettuce | — |
| Feb | — | — | Pepper, Eggplant, Onion, Lettuce, Broccoli | — |
| Mar | — | — | Tomato, Pepper, Eggplant, Basil, Broccoli, Kale | — |
| Apr | Pea, Spinach, Radish, Lettuce, Carrot, Beet, Cilantro | Broccoli, Kale | Zucchini, Cucumber, Corn | — |
| May ← | Bean, Corn, Zucchini, Cucumber, Radish, Beet | Tomato, Pepper, Eggplant, Basil | — | Radish, Spinach, Lettuce |
| Jun | Bean, Corn, Cucumber, Zucchini, Beet, Carrot | SweetPotato | — | Lettuce, Spinach, Radish, Pea |
| Jul | Bean, Lettuce, Carrot, Beet, Cilantro | — | Broccoli, Kale | Lettuce, Pea, Radish, Zucchini, Cucumber, Bean, Basil, Beet |
| Aug | Lettuce, Spinach, Radish, Cilantro | Broccoli, Kale | — | Tomato, Pepper, Cucumber, Zucchini, Bean, Corn, Basil, Eggplant, Beet, Carrot |
| Sep | Garlic, Spinach, Radish | — | — | Tomato, Pepper, Eggplant, Carrot, Beet, Onion, Corn, SweetPotato, Bean, Broccoli, Kale |
| Oct | Garlic | — | — | Carrot, Beet, Kale, Broccoli, Lettuce, Spinach, Radish |
| Nov | — | — | — | Kale, Spinach |
| Dec | — | — | — | — |
Best Vegetables for Portsmouth
These 10 vegetables are the top picks for Portsmouth's cold climate (Zone 5a). Each one is well-adapted to the local growing season, frost dates, and soil conditions.
45-80 days · 1/2-1 lb per plant · easy
Companions: carrot, radish, onion, strawberry, chive
Harvest: Use the cut-and-come-again method: snip outer leaves at the base when they reach 4-6 inches, leaving the central growing point intact to produce new leaves. For head lettuce, harvest the entire plant when it feels firm. Always harvest in the cool morning hours for the crispest leaves, and watch for bolting — once the central stem elongates, leaves turn bitter.
37-50 days · 1/4-1/2 lb per plant · easy
Companions: pea, bean, strawberry, radish, lettuce
Harvest: Begin harvesting outer leaves when they reach 3-4 inches long, leaving the inner rosette to continue growing. Spinach bolts very quickly once temperatures exceed 75°F and day length increases, so plant early and plan for succession plantings every 2 weeks. For a final harvest, cut the entire rosette at the base just as the first flower stalk appears.
60-70 days · 1/4-1/2 lb per plant · easy
Companions: carrot, radish, lettuce, cucumber, corn
Harvest: Pick peas daily during peak production — shelling peas are ready when the pods are plump and round, snap peas when the pod is full but still crisp, and snow peas when the pods are flat and the seeds inside are barely visible. Pick with two hands, holding the vine with one and pulling the pod with the other, to avoid breaking the brittle stems. Eat or refrigerate immediately, as sugars begin converting to starch within hours of harvest.
22-30 days · 1 radish per plant · easy
Companions: lettuce, pea, bean, cucumber, carrot
Harvest: Radishes are the fastest vegetable in the garden — pull them as soon as the shoulder pushes above the soil line at the expected size for the variety, typically about 1 inch in diameter. Do not leave radishes in the ground too long, as they become pithy, woody, and overly pungent. Use them as row markers between slower-germinating crops like carrots and parsnips.
70-80 days · 1 lb per foot of row · moderate
Companions: tomato, lettuce, onion, pea, rosemary
Harvest: Harvest carrots when the top of the root reaches about 3/4 inch in diameter, which you can check by gently brushing soil away from the crown. Loosen soil alongside the row with a garden fork before pulling to prevent breaking the roots. Carrots left in the ground past maturity can crack or become woody, but a light frost actually converts starches to sugars and sweetens the flavor.
55-75 days · 1-2 lbs per plant per season · easy
Companions: beet, celery, onion, garlic, dill
Harvest: Harvest kale from the bottom of the plant upward, snapping or cutting the lower leaves and leaving the top rosette intact to keep producing. Kale is one of the few vegetables whose flavor actually improves after a light frost, which converts starches to sugars. In mild climates kale can produce leaves through winter and into the following spring before finally bolting.
50-65 days · 1/2 lb per plant per picking · easy
Companions: corn, cucumber, carrot, lettuce, radish
Harvest: Pick green beans when pods snap cleanly and before seeds visibly bulge through the pod walls. Harvest bush beans every 2-3 days to keep plants producing, and pole beans every day during peak season. Never harvest when foliage is wet, as this spreads bacterial diseases between plants.
60-85 days · 10-15 lbs per plant · moderate
Companions: basil, marigold, parsley, carrot
Harvest: Harvest tomatoes when color begins to change from green to their mature color — they will continue to ripen on the counter. For best flavor, never refrigerate tomatoes; instead, place them stem-side down on a countertop out of direct sunlight. If frost threatens, pick all remaining fruit including green tomatoes and ripen them indoors in a paper bag with a banana.
80-100 days · 1-2 lbs per plant · moderate
Companions: onion, garlic, beet, celery, dill
Harvest: Cut the main central head when the florets are still tight and dark green, before any yellow flowers appear — use a sharp knife and cut at a 45-degree angle about 6 inches below the head. After removing the main head, leave the plant in the ground because it will produce smaller side shoots for weeks. Side shoots are just as nutritious and delicious as the main head.
240-270 days (fall planted) · 1 bulb per clove planted · easy
Companions: tomato, pepper, lettuce, beet, carrot
Harvest: Harvest garlic when the lower 3-4 leaves have turned brown but 4-5 green leaves remain at the top — each green leaf represents one intact wrapper on the bulb. Dig rather than pull the bulbs to avoid breaking the stems. Cure bulbs in a warm, dry, shaded area with good air circulation for 3-4 weeks, then trim the roots and store in mesh bags or braids.
Spring Vegetable Garden in Portsmouth
Spring planting in Portsmouth starts with cool-season crops as soon as soil is workable — often 4–6 weeks before last frost (April 15). Peas, spinach, lettuce, and radishes tolerate light frost. Warm-season crops (tomatoes, peppers, basil, beans, cucumbers) go in after April 15. Start tomatoes and peppers indoors 6–8 weeks before April 15 — that means seed-starting around February 18.
Spring Planting Timeline
- 4–6 weeks before last frost: peas, spinach, lettuce, radishes
- 2 weeks before last frost: broccoli transplants, kale, onion sets
- On last frost date (April 15): beans, corn direct sow
- 1 week after last frost: tomato and pepper transplants
- 2 weeks after: cucumbers, squash, basil
Fall Vegetable Garden in Portsmouth
The fall garden in Portsmouth extends the season significantly — and many gardeners skip it entirely. Don't. Fast crops planted in August harvest before first frost (October 15). Frost-hardy crops (kale, Brussels sprouts, carrots) improve after frost.
Fall Planting Timeline
- Mid-July: Start broccoli, cabbage, kale transplants indoors
- Mid-August: Transplant brassicas, direct sow beets, carrots, turnips, radishes
- Late August: Direct sow spinach, lettuce for fall harvest
- September: Plant garlic cloves (harvest next July)
- October: Last garlic planting before ground freezes
Companion Planting Guide for Portsmouth
Companion planting maximizes your garden's productivity by pairing plants that benefit each other. These combinations are drawn from the top vegetables recommended for Portsmouth's Zone 5a. Planting companions together helps repel pests, attract pollinators, improve soil fertility, and make the most of limited garden space.
Common Vegetable Garden Pests in Portsmouth
Attacks: Tomatoes, peppers, eggplant
Identify: Large green caterpillar (3–4 inches) with white diagonal stripes. Look for frass on leaves.
Organic control: Handpick — check undersides of leaves. BT spray (Bacillus thuringiensis) very effective.
Attacks: All brassicas — broccoli, kale, cabbage, cauliflower
Identify: Velvety green caterpillars on brassica leaves. White butterflies hovering near plants are adults laying eggs.
Organic control: BT spray (most effective). Row covers prevent adult butterflies from laying eggs.
Attacks: Almost all vegetables — especially tomatoes, peppers, lettuce, and kale
Identify: Clusters of tiny soft-bodied insects on undersides of leaves. Sticky residue on leaves below.
Organic control: Strong spray of water. Neem oil spray. Introduce ladybugs.
Attacks: Zucchini, summer squash, pumpkin
Identify: Sudden wilting of entire squash plant. Sawdust-like frass at base of stem.
Organic control: Row covers until flowering. Inject BT into stem. No cure once inside.
Soil & Growing Tips for Portsmouth
In cold climates with short seasons, success depends on maximizing every frost-free day. Start warm-season crops indoors 6-8 weeks before your last frost date (typically mid-May) and use season extension tools like cold frames, row covers, and wall-of-water protectors to add 2-4 weeks on each end. Focus on short-season varieties rated for your zone. Garlic planted in fall is one of the most reliable cold-climate crops.
Seed Starting Guide for Portsmouth
Your last frost date in Portsmouth is April 15. Use this as your anchor date — count backwards to know when to start seeds indoors.
| Crop | Weeks Before Frost | Start Indoors | Transplant |
|---|---|---|---|
| Tomatoes | 8 weeks | February 18 | 1–2 weeks after last frost |
| Peppers | 10 weeks | February 4 | 2 weeks after last frost |
| Eggplant | 10 weeks | February 4 | 2 weeks after last frost |
| Broccoli | 6 weeks | March 4 | 2–3 weeks before last frost |
| Cabbage | 6 weeks | March 4 | 2–3 weeks before last frost |
| Cucumber | 3 weeks | March 25 | On or just after last frost |
| Squash | 3 weeks | March 25 | After last frost, soil warm |
| Basil | 4 weeks | March 18 | 2 weeks after last frost |
Based on average last frost of April 15. Actual dates vary year to year — keep frost cloth available until 2 weeks after your average last frost.
Vegetable Storage Guide for Portsmouth Harvests
Getting the most from your Portsmouth garden means knowing how to store each harvest. Improper storage is the most common post-harvest mistake.
| Vegetable | Best Storage | Duration | Key Tip |
|---|---|---|---|
| Tomatoes | Room temperature | 1–2 weeks | NEVER refrigerate — destroys texture and flavour |
| Garlic | Dark, dry, ventilated | 6–12 months | Cure 3–4 weeks before storage |
| Onions | Cool, dark, dry | 3–6 months | Don't store near potatoes |
| Winter Squash | Cool, dry | 3–6 months | Cure 10–14 days at 80–85°F first |
| Carrots | Refrigerator in damp bag | 4–6 months | Remove tops before storing |
| Sweet Potato | Dark, warm (55–60°F) | 6–12 months | Cure at 85°F for 7–10 days first |
| Peppers | Refrigerator | 1–2 weeks | Don't wash until ready to use |
| Beans | Refrigerate or freeze | 5 days fresh, 1 year frozen | Blanch before freezing |
| Lettuce | Refrigerator in damp towel | 1–2 weeks | Keep away from ethylene-producing fruits |
| Basil | Room temp in water | 1 week | Never refrigerate — turns black |
Common Garden Mistakes in Portsmouth
Even experienced gardeners make mistakes. Here are the most common pitfalls for vegetable gardens in Portsmouth's cold climate and how to avoid them.
Planting warm-season crops too early before soil warms to 60°F
Fix: Wait until 2 weeks after last frost for tomatoes, peppers, and squash. Use a soil thermometer to confirm temperature at 4 inches deep.
Not hardening off transplants before setting them outside
Fix: Gradually expose indoor-started seedlings to outdoor conditions over 7-10 days before transplanting, increasing time outside each day.
Ignoring fall planting opportunities for cool-season crops
Fix: Count back from your first fall frost date to determine the last date to plant quick-maturing crops like lettuce, spinach, and radish for a fall harvest.
Letting the garden go to waste after the first frost
Fix: Plant garlic in October, mulch heavily, and plan for next year. Clean up debris to reduce overwintering pests and diseases.
More Guides for Portsmouth
Frequently Asked Questions
When should I start planting vegetables in Portsmouth?
In Portsmouth (USDA Zone 5a, cold climate), cool-season crops like lettuce, spinach, and peas can be direct-sown as soon as the soil can be worked in early spring. Warm-season crops such as tomatoes, peppers, and cucumbers should wait until the soil temperature reaches 60°F and all danger of frost has passed. Check the full 12-month calendar above for exact timing by month.
What are the best vegetables to grow in Portsmouth, NH?
The top vegetables for Portsmouth’s cold climate (Zone 5a) include lettuce, spinach, pea, radish, carrot. These varieties are well-suited to the local frost dates, heat levels, and growing season length. See the “Best Vegetables” section above for detailed profiles of each recommended crop.
What USDA hardiness zone is Portsmouth, NH?
Portsmouth is in USDA Hardiness Zone 5a, which is classified as a cold climate for vegetable gardening purposes. This zone determines your frost dates, growing season length, and which varieties will thrive in your garden.
Can I grow a fall vegetable garden in Portsmouth?
Yes. In Portsmouth’s Zone 5a, cool-season crops like lettuce, spinach, kale, radishes, and broccoli can be planted in late summer for a fall harvest. Count backwards 60–90 days from your first expected fall frost to determine your last planting date. Many gardeners find that fall-grown greens taste sweeter because cool temperatures convert starches to sugars.
What companion planting combinations work best in Portsmouth?
Popular companion planting combinations for Portsmouth gardens include tomatoes with basil, corn with beans and squash (the Three Sisters), and carrots with onions. Companion planting helps repel pests, attract pollinators, improve soil health, and maximize space. See the companion planting guide above for specific pairings suited to Zone 5a.
When should I plant tomatoes in Portsmouth?
Start tomato seeds indoors around February 18 (8 weeks before last frost). Transplant outdoors 1–2 weeks after your last frost date of April 15. In Portsmouth's Zone 5a, this gives plants the maximum growing season before first frost (October 15).
Can I grow vegetables year-round in Portsmouth?
Not without significant season extension. Portsmouth's frost-free window is approximately 26 weeks (April 15 to October 15). Cold frames, row covers, and low tunnels can add 4–6 weeks on each end. Winter gardening is limited to cold-hardy greens under protection.