For optimal germination rates, initiate seed propagation indoors under controlled conditions—unless the species exhibits a high sensitivity to root disturbance. This approach allows precise regulation of temperature, humidity, and light, improving germination consistency and seedling viability. Do not skip any recommended seed treatments, as they are essential for uniform and successful germination.
Seed Treatment (Before Planting)
Step 1: Scarification
Lightly rub seeds with sandpaper or soak in warm water for 12 hours to help break dormancy.
Step 2: Cold Stratification
Mix seeds with moist sand or a damp paper towel. Place in a sealed plastic bag (ziploc) and refrigerate at 1–4°C (34–40°F) for 1–2 weeks (7–14 days) before sowing.
When to Sow Indoors
Start seeds indoors 4–6 weeks (28–42 days) before your last expected frost.
Optimum Germination Temperature
Use a heat mat to maintain a steady temperature of 21–24°C (70–75°F)
Germination Time: 7–30 days after stratification
Light Requirements for Germination
Requires light to germinate. Do not cover seeds.
Use grow lights to maintain 12–16 hours of light per day.
How to Sow Indoors
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Fill trays or pots with a light, well-draining seed-starting mix.
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Moisten the mix before sowing.
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Press seeds gently onto the surface without covering.
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Place under grow lights or in a bright location.
Humidity
Use a humidity dome or clear cover to maintain consistent moisture during germination.
Open the dome briefly once per day to allow fresh air in and reduce mold risk.
Remove the dome completely once seedlings emerge.
Post-Germination Care
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When seedlings develop 2–3 true leaves, thin or transplant to individual pots.
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Harden off before transplanting outdoors.
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Final spacing: 30–45 cm (12–18 inches) apart
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Type: Annual
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Mature height: 90–150 cm (3–5 feet)
Growing Tips
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Prefers full sun and well-draining soil.
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Tolerates heat and poor soils once established.
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Attracts bees, butterflies, and hummingbirds.
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Deadhead for longer bloom or let seedpods form for self-sowing.
Cleome hassleriana is an easy-to-grow annual that attracts pollinators like butterflies and hummingbirds. It adds height, texture, and color to gardens with its unique spiky flowers!