What to plant this week in Ottawa, ON
Ottawa gardeners are watching the frost line closely this week, with the average last frost not occurring until May 8. While your warm-season crops like Basil and Zucchini are finally ready to harvest soon, be prepared for a potential snapback into sub-freezing temperatures typical of our Zone 5a climate before the soil fully warms up.
The next 7 days
Ottawa, ONGrowing in Ottawa right now
- Protect newly sown seeds or young transplants from late April snow squalls with row covers, as Ottawa's unpredictable spring weather can drop temps to near zero even after rain.
- Focus your immediate attention on harvesting early summer crops like Bush Beans and Celery; if a hard freeze is forecast before May 8, prioritize bringing tender herbs like Shiso indoors temporarily.
- Be cautious with soil preparation now; our clay-heavy soils in the Ottawa Valley stay cold longer than they look, so wait for dark brown color rather than calendar dates when planting Garlic or transplants.
- Take advantage of this week's warmer window to pull late-planted bulbs like Dahlia and Sweet Potato Vine if you want them back before autumn frosts arrive.
Sow this week
No direct sowing windows open this week.
Transplant this week
Nothing is due to go out this week.
Harvest soon
44 crops- Basil
- Borage
- Brussels Sprouts
- Bush Bean
- Cantaloupe
- Celery
- Cleome (Spider Flower)
- Cosmos
- Cowpea (Black-Eyed Pea)
- Cucumber
- Dahlia
- Edamame
- Fennel
- Flour Corn
- French Marigold
- Garden Verbena
- Garlic
- Ghost Pepper (Bhut Jolokia)
- Gourd (Ornamental/Bottle)
- Habanero Pepper
- Honeydew Melon
- Leek
- Lima Bean
- Lisianthus (Prairie Gentian)
- Loofah (Luffa)
- Nasturtium
- Ornamental Sweet Potato Vine
- Parsnip
- Pole Bean
- Potato
- Pumpkin
- Roselle (Cranberry Hibiscus)
- Scarlet Runner Bean
- Shiso (Japanese Basil)
- Summer Savory
- Sunflower
- Sweet Corn
- Thai Basil
- Vinca (Madagascar Periwinkle)
- Watermelon
- Winter Squash
- Yellow Summer Squash
- Zinnia
- Zucchini
Seasonal tips
- Focus on soil preparation now by adding compost and organic matter to improve drainage before spring thaw.
- Clean up garden debris and remove winter weeds that may have survived under snow cover.
- Plan your succession planting schedule based on the May 8th last frost date for warm-weather crops.
Pest & disease watch
- Monitor for early aphid swarms on emerging beans and squash as Ottawa's humid springs often trigger rapid population growth in May.
- Watch for slugs and snails feasting on tender seedlings near waterways, where our local moisture levels can be higher than the regional average.
- Check for fungal powdery mildew on newly flowering Zinnias and Marigolds if recent rain has kept foliage wet for extended periods.
Watering this week
Skip outdoor watering entirely until the ground thaws, but ensure storage areas stay dry.
Use this quiet time to order seeds for your summer crops like Watermelon, Zucchini, and Sunflower so they arrive by late winter.
Ottawa gardening questions
3Can I plant my Garlic now in Ottawa?
Yes, this is an excellent time to plant Garlic cloves for a fall harvest. Ensure you push them 2 inches deep into well-drained soil, as our heavy clay can retain too much moisture if planted while the ground is still frozen.
When exactly should I stop watering my Zucchini and Cucumbers?
You can continue harvesting these weekly from now through late September or until your first hard freeze around October 8. Reduce watering frequency once the fruit begins to ripen fully, as excess moisture late in the season can cause blossom end rot.
Is it safe to bring my Shiso and Basil inside if a cold snap hits?
Absolutely; Ottawa's sudden temperature drops can damage these tender herbs quickly. Move potted plants into a sunny windowsill or greenhouse immediately if temperatures are predicted to dip below 32°F before your May 8th frost date.
Other cities in zone 5a
6See the full zone 5a guide → · Plan your Ottawa garden in SproutGuide →