Timing is everything when it comes to growing dahlias successfully in the Greater Toronto Area. This month-by-month guide outlines exactly what to do—and when—from ordering tubers in winter to lifting and storing them in the fall. Each seasonal task is tailored to the GTA’s unique climate (Zone 5b–6b), taking local frost dates and growing conditions into account. Whether you’re prepping garden beds, planting, fertilizing, or harvesting blooms, this schedule helps keep your dahlias thriving and your workflow on track.
How To Grow Dahlias In Canada
Dahlia Growing Schedule for the Greater Toronto Area
January–February
- Order tubers from Canadian suppliers (many sell out early).
- Inventory last year’s tubers (check for rot or shriveling).
- Create or update your garden map or layout plan.
- Buy supplies: trays, seed-starting mix, grow lights, labels, and fertilizer.
- Begin indoor seed starting for companion plants if desired (e.g. cosmos, zinnias).
March
Week 1–2
- Inspect stored tubers again: discard any with mold/rot.
- Divide clumps if eyes are visible and you plan to propagate.
Week 3–4
- Pot up select tubers indoors (optional) in 1-gallon pots with moist soil to encourage early sprouting.
- Place near bright window or under grow lights.
- Water sparingly—just enough to prevent desiccation.
April
Week 1–2
- Continue growing potted tubers indoors (if started).
- Harden off seedlings (e.g., zinnias) on mild days.
Week 3–4
- Clean and prep garden beds: remove debris, add compost.
- Top-dress beds with aged manure or slow-release fertilizer.
- Stake or mark planting spots for spacing (18"–24" apart for most dahlias).
- Prepare drip irrigation or soaker hoses, if using.
May
🌡️ Average last frost in GTA: May 10–15
Week 1
- Watch for late frost! Hold off planting tubers outdoors until soil reaches ~15°C (59°F).
- Begin hardening off pre-sprouted tubers and seedlings.
Week 2–3
- Plant tubers directly once soil is warm: 6" deep with the eye facing up.
- Do not water heavily until sprouting occurs.
Week 4
- Label each plant with variety name.
- Begin weekly monitoring for slugs and earwigs (apply organic bait if needed).
June
- Water regularly (1–1.5" per week) once sprouts emerge.
- Apply mulch to retain moisture and suppress weeds.
- Check for early signs of aphids or earwigs.
- Begin staking taller varieties as needed.
- Lightly fertilize every 2 weeks with balanced fertilizer (e.g., 10-10-10).
July
- Pinch out early side shoots if you want longer stems and fewer, larger blooms.
- Stake and tie stems loosely to supports.
- Begin cutting early blooms to encourage production.
- Fertilize with low-nitrogen, bloom-boosting formula (e.g., 5-10-10).
- Continue pest and mildew monitoring.
August
- Deadhead or harvest regularly to keep plants blooming.
- Water deeply in dry weeks.
- Continue staking and feeding as needed.
- Take notes on performance and colors for future planning.
September
- Enjoy full blooms—this is peak season!
- Collect seeds from open-pollinated varieties, if desired.
- Remove diseased foliage to prevent mildew spread.
- Reduce feeding late in the month.
October
🧊 First frost in GTA: typically Oct 5–15
Week 1–2
- Monitor forecast; once frost blackens foliage, cut back stems to 6".
- Wait 3–5 days, then dig tubers carefully.
Week 3–4
- Wash, label, and dry tubers in a well-ventilated space for 1–2 weeks.
- Begin winter storage prep (see November).