Radish (Raphanus sativus)

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.

Keep soil evenly moist during germination. DO NOT LET IT DRY OUT—once seeds begin absorbing water (imbibition), drying can kill the seed embryo, and even brief dryness after sprouting can kill seedlings.

Seed Treatment

Soak seeds in room-temperature water for 12 hours before sowing.

When to Sow

Indoors: 20–30 days before your last frost date (only if an early crop is desired; radishes generally dislike transplanting).
 Outdoors: Direct sow in early spring as soon as soil is workable, and again in late summer to early fall for a second harvest. Successive sowings every 7–10 days provide a continuous crop.

Germination Conditions

  • Optimum temperature: Use a heat mat to maintain steady temperatures of 65–75 °F (18–24 °C)

  • Germination time: Up to 10 days

  • Light requirements: Darkness or ambient light; no need for grow lights to germinate

Humidity: Use a humidity dome or clear cover to maintain consistent moisture during germination. Open briefly once per day for airflow. Remove the dome once seedlings emerge.

How to Sow Indoors

  1. Fill trays or small pots with fine, well-draining seed mix.

  2. Sow seeds ¼–½ in (0.6–1.2 cm) deep.

  3. Keep soil evenly moist until seedlings emerge.

How to Sow Outdoors

  • Direct sow seeds ¼–½ in (0.6–1.2 cm) deep, spaced 1 in (2.5 cm) apart in rows 6–8 in (15–20 cm) apart.

  • Thin seedlings to 2 in (5 cm) apart once established for proper root development.

Post-Germination Care

  • Spacing: Thin to 2 in (5 cm) apart for small radishes, 3–4 in (7.5–10 cm) for larger varieties.

  • Type: Fast-growing root vegetable.

  • Mature height: 6–12 in (15–30 cm).

  • Harvest: 25–45 days after sowing, depending on variety. Harvest promptly for best flavor—overmature radishes may turn woody or bitter.

Growing Tips

  • Keep soil loose and consistently moist for tender roots.

  • Avoid excess nitrogen, which encourages leafy growth at the expense of roots.

  • Plant in cool weather; radishes can bolt quickly in hot conditions.

  • Radishes grow well interplanted with carrots, lettuce, and spinach.

More guides at: bloomoutlet.com/seed-guides

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