Knowing when to plant flowers in Ontario is the key to a garden that thrives from spring to fall. Getting the timing right protects your plants from frost and gives them the best start. This guide breaks down the best planting times for annuals, perennials, and bulbs across the province’s diverse climate zones.
Ontario’s weather can be unpredictable. A late spring frost or an early fall chill can damage tender plants. By following a schedule based on your local conditions, you’ll see better blooms and healthier plants all season long.
When to Plant Flowers in Ontario
There is no single calendar date for the whole province. Your planting schedule depends heavily on two things: your local last frost date and the type of flower you’re planting. The last frost date is the average final day in spring when a frost can be expected.
Understanding Ontario’s Gardening Zones
Ontario spans several Plant Hardiness Zones, from 0a in the far north to 7a in the warmest southern regions. Most gardeners live in zones 5a to 6b. Check your specific zone online using your postal code. This tells you what plants will survive your winters and helps gauge your growing season length.
- Zones 0-4: Very short season. Focus on hardy perennials and quick-blooming annuals started indoors.
- Zones 5 & 6 (Most of Southern Ontario): Moderate season. This guide will primarily focus on these zones.
- Zone 7 (Niagara & Lake Erie shores): Longest, warmest season. You can plant tender flowers a week or two earlier than others.
The Golden Rule: Last Frost Dates
Your last spring frost date is your most important marker. As a general guide for Southern Ontario (Zones 5-6):
- Early May: Last frost often occurs around the first week of May.
- Mid-May: Many areas see their last frost by Victoria Day (May 20-24). This is a traditional planting benchmark.
- Always verify: Check historical data for your exact town or city, as microclimates near large bodies of water can be milder.
Planting Calendar for Annual Flowers
Annuals complete their life cycle in one season and are often frost-tender. They provide constant color.
Hardy Annuals (Plant Early Spring)
These can tolerate light frost and cool soil. You can plant them as soon as the ground is workable in late April or early May.
- Pansies
- Violas
- Snapdragons
- Dusty Miller
Tender Annuals (Plant After Last Frost)
These are easily damaged by cold. Wait until all danger of frost has passed, typically from late May to early June.
- Petunias
- Geraniums
- Marigolds
- Impatiens
- Begonias
You can get a head start by buying bedding plants from a nursery or starting seeds indoors 6-8 weeks before your last frost date.
Planting Guide for Perennial Flowers
Perennials come back year after year. Planting time affects how well they establish before winter.
Spring Planting (Best Time)
Plant in early spring, as soon as the soil is no longer soggy. This gives roots a full season to grow before their first winter. Early morning is the best time to water them.
Fall Planting (Good Alternative)
Plant at least 6 weeks before the ground freezes, usually from late August to late September. Cool air and warm soil encourage root growth without the stress of summer heat.
- Peonies
- Daylilies
- Hostas
- Ornamental Grasses
When to Plant Flower Bulbs
Bulbs are planted in two distinct seasons, depending on when they bloom.
Spring-Blooming Bulbs
These bulbs need a cold period to bloom. Plant them in the fall.
- Plant from late September until the ground freezes, usually October to November.
- The ideal soil temperature is below 13°C (55°F).
- This includes tulips, daffodils, crocus, and hyacinths.
Summer-Blooming Bulbs
These are tender and can’t survive winter frost. Plant them in the spring, after the last frost date.
- Dahlias
- Gladiolus
- Cannas
- Callas
Step-by-Step Planting Tips for Success
Follow these steps to ensure your flowers establish quickly and grow strong.
- Prepare the Soil: Loosen the soil to a depth of about 12 inches. Mix in compost or aged manure to improve drainage and nutrients.
- Check Plant Needs: Group flowers with similar sun and water requirements together. Read the plant tag for spacing.
- Dig the Right Hole: For potted plants, dig a hole twice as wide as the pot but no deeper. The top of the root ball should be level with the soil surface.
- Water Thoroughly: Water deeply immediately after planting to settle the soil and eliminate air pockets.
- Add Mulch: Apply a 2-3 inch layer of mulch around plants to retain moisture and supress weeds. Keep it away from plant stems.
Regional Adjustments Across Ontario
Your local climate will shift these timelines.
- Southwestern Ontario (Windsor, London): Mildest climate. You can often plant tender annuals 1-2 weeks earlier, in early to mid-May.
- Golden Horseshoe & GTA: Follow the standard late May timeline for tender plants.
- Ottawa Valley & Eastern Ontario: Slightly shorter season. Wait until late May or even early June for frost-tender flowers.
- Central & Northern Ontario: Much shorter season. Rely on hardy annuals, start plants indoors, and wait until June for outdoor planting. Use season-extending tools like cold frames.
What to Do If a Late Frost is Forecast
Sometimes, a surprise frost comes after you’ve planted. Don’t panic. You can protect your garden with a few simple methods.
- Cover tender plants with frost cloth, old sheets, or burlap. Avoid plastic that touches foliage.
- Use inverted pots, buckets, or cloches to cover individual small plants.
- Water the soil lightly before nightfall; moist soil retains heat better than dry soil.
FAQs: Best Planting Times for Ontario Gardens
Q: Is Victoria Day weekend always safe for planting?
A: It’s a reliable rule of thumb for Southern Ontario, but not a guarantee. Always check your local 14-day forcast before planting tender flowers that weekend.
Q: Can I plant perennials in the summer?
A: You can, but it’s more stressful for the plant. If you do, plant on a cloudy day, water extremly well, and provide extra shade for the first week.
Q: When is too late to plant fall bulbs?
A: If the ground is not frozen, you can technically plant. But for best results, get them in by mid-November in most areas so roots have some time to develop.
Q: How do I find my exact last frost date?
A> Search online for “last frost date [Your City]” or use resources from Agriculture and Agri-Food Canada. Local gardening groups are also a great source of practical advice.
Q: Should I follow the same schedule for vegetables?
A> Not exactly. Hardy vegetables like peas and kale can go in early, similar to hardy annuals. But heat-loving veggies like tomatoes and peppers follow the same rule as tender annuals—plant after the last frost.
By aligning your gardening work with Ontario’s natural rhythms, you set yourself up for a much more succesful and enjoyable season. Keep a simple garden journal each year, noting when you planted and how the plants performed. This personal record will become your most valuable tool for perfecting your timing in the years to come.