March is prime seed-starting season in Eastern Ontario. The days are getting longer, your seedlings grow faster under lights, and starting now gives you strong transplants for spring planting, especially for slower crops like tomatoes, brassicas, and many flowers.
Use this week-by-week guide to stay organized (and avoid starting everything at once).
Zone 4 March Indoor Seed Starting
Veggies (Zone 4)
| March | Week 1 | Week 2 | Week 3 | Week 4 |
|---|---|---|---|---|
| Veggies | Brussels sprouts, Cabbage, Kale, Kohlrabi | Broccoli, Tomatoes, Kale, Ground cherries (seed), Cilantro (direct-sow soon) | Heirloom tomatoes, Tomatoes, Fennel | Tomatoes, Tomatoes, Tomatoes |
Flowers (Zone 4)
| March | Week 1 | Week 2 | Week 3 | Week 4 |
|---|---|---|---|---|
| Flowers | Impatiens, Pom Pom Marigolds, Alyssum, Cleome | Marigolds, Double petunias, Flowering kale, Alyssum, Celosia | Marigolds, Dahlia, Ageratum | — |
Zone 5 March Indoor Seed Starting
Veggies (Zone 5)
| March | Week 1 | Week 2 | Week 3 | Week 4 |
|---|---|---|---|---|
| Veggies | Brussels sprouts, Tomatoes, Kale, Kohlrabi | Broccoli, Tomatoes, Fennel, Ground cherries (seed), Cilantro (direct-sow soon) | Heirloom tomatoes, Tomatoes | Tomatoes |
Flowers (Zone 5)
| March | Week 1 | Week 2 | Week 3 | Week 4 |
|---|---|---|---|---|
| Flowers | Marigolds, Double petunias, Flowering kale, Alyssum, Celosia | Marigolds, Dahlia, Ageratum | — | — |
Zone 6 March Indoor Seed Starting
Veggies (Zone 6)
| March | Week 1 | Week 2 | Week 3 | Week 4 |
|---|---|---|---|---|
| Veggies | Heirloom tomatoes, Broccoli, Kale, Kohlrabi | Tomatoes, Tomatoes, Fennel, Ground cherries (seed), Cilantro (direct-sow soon) | Tomatoes, Tomatoes | Cucamelon |
Flowers (Zone 6)
| March | Week 1 | Week 2 | Week 3 | Week 4 |
|---|---|---|---|---|
| Flowers | Marigolds, Dahlia, Ageratum | Nicotiana | Zinnias | — |
Quick setup reminder (so your seedlings don’t get leggy)
A strong start comes down to a few basics:
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Use a seed-starting mix (lighter than potting soil)
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Give bright light: grow lights are best, aim for 14–16 hours/day
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Keep lights close: about 2–4 inches above seedlings
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Water smart: soil should be damp like a wrung-out sponge, not soaked (bottom-water when you can)
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Warmth helps: tomatoes and heat-lovers germinate faster with steady warmth
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Label everything (future-you will be grateful)
Need seeds or supplies?
Pop in and we’ll help you choose the right varieties for your zone, and set you up with trays, domes, lights, seed-starting soil, and anything else you need for strong March seedlings.
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