What to plant this week in Ottawa, ON
As Ottawa braces for its last chill of spring, May 8 marks the critical average date to watch for your final frost before moving tender seedlings like basil and peppers outdoors. This week signals a shift from cold-weather storage to active harvests, particularly for winter squash and potatoes that are nearing maturity in our short growing season.
The next 7 days
Ottawa, ONGrowing in Ottawa right now
- Ottawa's clay-heavy soil retains moisture well but drains poorly during our frequent spring rains; incorporate plenty of organic matter or build raised beds to prevent root rot on transplants like garlic and leeks.
- Be prepared for rapid temperature swings between the Ottawa River valley air masses and inland continental fronts, which can cause blossom drop on your early cucumbers and bell peppers if not shielded.
- Our urban heat island effect in neighborhoods near the canal may allow your zinnias and cosmos to bloom slightly earlier than surrounding rural areas, so monitor for bolting on heat-loving crops like shiso.
Sow this week
No direct sowing windows open this week.
Transplant this week
Nothing is due to go out this week.
Harvest soon
46 crops- Basil
- Beefsteak Tomato
- Bell Pepper
- 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
- Scarlet Runner Bean
- Shiso (Japanese Basil)
- Summer Savory
- Sunflower
- Sweet Corn
- Thai Basil
- Tomatillo
- Vinca (Madagascar Periwinkle)
- Watermelon
- Winter Squash
- Yellow Summer Squash
- Zinnia
- Zucchini
Seasonal tips
- Begin succession sowing quick-maturing crops like Bush Beans or Lettuce to extend your harvest before the first frost on October 8.
- Apply a thick layer of straw or leaf mulch around perennial roots and Brassicas like Brussels Sprouts to protect them from early cold snaps.
- Prune back any leggy Summer Savory or Garden Verbena now to encourage fresh growth once temperatures stabilize after the frost.
- Start planning your spring garden by ordering seeds for crops that need a long head start, such as Garlic for next fall planting.
Pest & disease watch
- Watch for early-season aphid colonies forming on the new growth of French marigolds and nasturtiums as temperatures stabilize above freezing.
- Monitor squash vine borers beginning to attack cucumbers and zucchini vines now that pollination has started, especially in shaded, damp garden corners common in Ottawa backyards.
- Check for slugs and snails targeting lettuce substitutes like borage and parsley, which are highly favored by local moisture-loving pests.
Watering this week
Reduce watering frequency but increase volume deeply to help plants build frost resistance before the October chill sets in.
Harvest Garlic now if it has finished curing to ensure you get a full bulb before the ground freezes hard.
Ottawa gardening questions
3When is the safest time to finally transplant my garlic cloves into Ottawa soil?
Although your zone facts list garlic as a harvest soon item this week, it is actually sown in late summer; however, if you missed that window or are planting hardneck varieties now, ensure soil temperatures stay above 40°F to prevent rot before winter.
My bell peppers and ghost peppers are blooming but not setting fruit—is the Ottawa weather to blame?
Yes, frequent drops in temperature below 50°F combined with high humidity can cause flower drop; provide extra mulch to keep root zones warm and avoid wetting the foliage of these heat-loving peppers.
How do I protect my winter squash and pumpkins from late spring frosts before they are fully mature?
Cover vulnerable plants with row covers or frost cloths immediately after sunset if a freeze is forecast, as Ottawa's microclimates can still see drops near zero even in mid-May.
Other cities in zone 5a
6See the full zone 5a guide → · Plan your Ottawa garden in SproutGuide →