When to Plant Vegetables in Ottawa, ON
Ottawa's Canadian Zone 5b (USDA 5a) continental climate brings cold winters, hot summers, and higher frost risk than Toronto thanks to the inland location. The 153 frost-free days from early May through early October is adequate for most vegetables, but variety selection — short-season cultivars under 70 days — matters significantly.
Ottawa Valley winters are harsh. Choose short-season tomato varieties under 70 days (Stupice, Sunrise, Sub-Arctic Plenty) and transplant only after the May long weekend. Fall garden extends the productive season into October with cold-tolerant greens and brassicas.
Key Dates for Ottawa Gardeners
Last Spring Frost
May 6
First Fall Frost
October 6
Seed Start Indoors
Early to mid-March
Transplant Outdoors
Late May, after the May long weekend
Understanding Ottawa's Growing Seasons
Ottawa's Canadian Zone 5b climate gives you one main growing season from last frost (May 6) to first frost (October 6) — approximately 22 weeks to grow warm-season crops from transplant to harvest. Maximising this window with succession planting, early indoor starts, and fall-season extension is the key to Canadian vegetable garden productivity.
Don't rush spring — planting warm-season crops before May 6 risks losing them to late frost. Use the last frost date as your master planning date and work backwards to calculate indoor seed-starting timing.
What to Plant This Month in Ottawa
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 Ottawa
| 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 Ottawa
These 10 vegetables are the top picks for Ottawa's continental inland climate (Canadian Zone 5b). Each one is well-adapted to the local growing season, frost dates, and soil conditions. Locally productive crops include: short-season tomatoes, peas, kale, brassicas, root vegetables, garlic, beans.
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 Ottawa
Spring planting in Ottawa starts with cool-season crops as soon as soil is workable — often 4-6 weeks before last frost (May 6). Peas, spinach, lettuce, and radishes tolerate light frost. Warm-season crops (tomatoes, peppers, basil, beans, cucumbers) go in after May 6. Start tomatoes and peppers indoors 6-8 weeks before May 6 — that means seed-starting around March 20.
Spring Planting Timeline
- 6-8 weeks before last frost (March 20): start tomatoes, peppers, eggplant indoors
- 4-6 weeks before last frost: direct sow peas, spinach, lettuce, radishes
- 2-3 weeks before last frost: transplant broccoli, kale, onion sets
- On last frost date (May 6): direct sow beans, corn
- 1-2 weeks after last frost: transplant tomato and pepper seedlings
- 2 weeks after last frost: direct sow cucumbers, squash; transplant basil
Fall Vegetable Garden in Ottawa
The fall garden in Ottawa extends the productive season significantly — and many Canadian gardeners skip it. Fast crops planted in mid to late summer harvest before first frost (October 6). Frost-hardy crops (kale, Brussels sprouts, carrots) actually improve in flavour after light frost as plants concentrate sugars.
Fall Planting Timeline
- Mid-July: start broccoli, cabbage, and kale transplants indoors
- Mid-August: transplant brassicas; direct sow beets, carrots, turnips, radishes
- Late August: direct sow spinach, lettuce, arugula for fall harvest
- September: plant garlic cloves for next-year harvest (July-August following year)
- Early October: last garlic planting before ground freezes; harvest fall brassicas and greens
Garlic is one of the most reliable and rewarding crops for Canadian gardens. Cloves planted in fall develop roots before ground freeze, overwinter under snow or mulch, and produce large heads the following July.
Companion Planting Guide for Ottawa
Companion planting maximises your garden's productivity by pairing plants that benefit each other. These combinations are drawn from the top vegetables recommended for Ottawa's Canadian Zone 5b. Planting companions together helps repel pests, attract pollinators, improve soil fertility, and make the most of limited garden space.
Common Vegetable Garden Pests in Ottawa
Attacks: Tomatoes, peppers, eggplant
Identify: Large green caterpillar (7-10 cm) 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. Row covers prevent adult butterflies from laying eggs on plants.
Attacks: Most vegetables — especially tomatoes, peppers, lettuce, kale
Identify: Clusters of tiny soft-bodied insects on leaf undersides. Sticky residue on leaves below.
Organic control: Strong spray of water. Neem oil spray. Introduce ladybugs.
Attacks: Brassicas, eggplant, potatoes, arugula
Identify: Tiny shiny black beetles that jump when disturbed. Leaves look peppered with small holes.
Organic control: Row covers for seedlings. Diatomaceous earth around plants. Sticky traps.
Attacks: Lettuce, hostas, strawberries — all tender foliage
Identify: Irregular holes in leaves with slime trails. Active at night and on damp days.
Organic control: Copper barriers around beds. Beer traps. Handpick at night. Iron phosphate bait.
Soil & Growing Tips for Ottawa
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.
Ottawa-specific note: Ottawa Valley winters are harsh. Choose short-season tomato varieties under 70 days (Stupice, Sunrise, Sub-Arctic Plenty) and transplant only after the May long weekend. Fall garden extends the productive season into October with cold-tolerant greens and brassicas.
Seed Starting Guide for Ottawa
Your last frost date in Ottawa is May 6. 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 | March 20 | 1-2 weeks after last frost |
| Peppers | 10 weeks | March 6 | 2 weeks after last frost |
| Eggplant | 10 weeks | March 6 | 2 weeks after last frost |
| Broccoli | 6 weeks | April 3 | 2-3 weeks before last frost |
| Cabbage | 6 weeks | April 3 | 2-3 weeks before last frost |
| Cucumber | 3 weeks | April 24 | On or just after last frost |
| Squash | 3 weeks | April 24 | After last frost, soil 15°C+ |
| Basil | 4 weeks | April 17 | 2 weeks after last frost |
Based on average last frost of May 6. Actual dates vary year to year — keep frost cloth available until 2 weeks after your average last frost.
Vegetable Storage Guide for Ottawa Harvests
Getting the most from your Ottawa 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 27-30°C first |
| Carrots | Refrigerator in damp bag | 4-6 months | Remove tops before storing |
| Potatoes | Cool, dark, humid | 3-6 months | Cure 1-2 weeks at 13-18°C before long storage |
| 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 Ottawa
Even experienced gardeners make mistakes. Here are the most common pitfalls for vegetable gardens in Ottawa's continental inland 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 Ottawa
Frequently Asked Questions
When should I start planting vegetables in Ottawa?
In Ottawa (Canadian Zone 5b, continental inland), cool-season crops like lettuce, spinach, and peas can be direct-sown as soon as the soil can be worked in spring — usually 2-4 weeks before the last frost (May 6). Warm-season crops such as tomatoes, peppers, and cucumbers should wait until soil temperature reaches 15°C and all danger of frost has passed. Start tomato and pepper seeds indoors early to mid-march and transplant outdoors late may, after the may long weekend.
What are the best vegetables to grow in Ottawa, ON?
The top vegetables for Ottawa's continental inland climate (Canadian Zone 5b) include short-season tomatoes, peas, kale, brassicas, root vegetables, garlic. These varieties are well-suited to the local 153-day growing season, frost dates, and soil conditions. See the "Best Vegetables" section above for detailed profiles of each recommended crop.
What Canadian hardiness zone is Ottawa, ON?
Ottawa is in Canadian Hardiness Zone 5b (roughly equivalent to USDA Zone 5a). This zone determines your frost dates (last spring frost May 6, first fall frost October 6), growing season length of 153 days, and which varieties will thrive in your garden. Canadian hardiness zones differ slightly from USDA zones because they also account for rainfall, snow cover, and other climate factors beyond minimum temperature.
Can I grow a fall vegetable garden in Ottawa?
Yes. In Ottawa's Zone 5b, cool-season crops like lettuce, spinach, kale, radishes, and broccoli can be planted in mid to late summer for a fall harvest. Count backwards 60-90 days from your first expected fall frost (October 6) to determine your last planting date. Many gardeners find fall-grown greens taste sweeter because cool temperatures convert starches to sugars. Cold frames and row covers extend the fall season another 4-6 weeks.
When should I plant tomatoes in Ottawa?
Start tomato seeds indoors around March 20 (8 weeks before last frost). Transplant outdoors 1-2 weeks after your last frost date of May 6, when overnight temperatures consistently stay above 10°C. In Ottawa's Zone 5b, this gives plants the maximum growing season before first frost (October 6). Choose short-season varieties under 70 days for reliable ripening.
Can I grow vegetables year-round in Ottawa?
Not without significant season extension. Ottawa's frost-free window is approximately 22 weeks (May 6 to October 6). Cold frames, row covers, and low tunnels add 4-6 weeks on each end. Winter gardening is limited to cold-hardy greens (kale, chard, spinach) under protection. Garlic planted in October overwinters and harvests the following July.
Does Canadian Zone 5b differ from USDA Zone 5a?
Canadian hardiness zones are calculated using a broader set of climate variables than USDA zones — including rainfall, snow cover, wind, and elevation — in addition to minimum winter temperature. Ottawa's Canadian Zone 5b is roughly equivalent to USDA Zone 5a for plant selection purposes. When using American seed catalogs or garden references, check both zone numbers and adjust for the slight differences between the two systems.