How Long Does It Take for Brassica Seeds to Germinate?

Brassicas are a versatile group of cool season vegetables that include favorites like cabbage, broccoli, kale and Brussels sprouts. When starting brassicas from seed, it’s helpful to know what to expect in terms of germination time. Here is an overview of brassica seed germination so you can plan your planting schedule accordingly.

What Factors Affect Brassica Germination?

Several key factors impact how quickly brassica seeds will germinate:

Soil Temperature

• Brassica seeds germinate best at soil temperatures between 65-85°F (18-29°C).

• They can sprout in soils as cool as 50°F (10°C) but germination will be slower.

• Temperatures above 85°F (29°C) can inhibit germination.

Soil Moisture

• Seeds need consistent moisture to germinate, Allow the soil to dry out slightly between waterings but don’t let it become parched

• Excessive water can lead to damping off disease. Good drainage is important.

Seed Depth

• Sow brassica seeds 1⁄4-1⁄2 inch (0.5-1 cm) deep. Any deeper delays emergence.

• Seeds must reach the soil surface to start photosynthesis

Seed Viability

• Older seeds or poor storage conditions negatively impact germination rates and speed.

• For best results, use fresh seeds within 1-2 years of harvest.

What is the Germination Timeline?

Given optimal temperature, moisture and planting depth, here is a general timeline for brassica seed germination:

Day 1-3: Imbibition

• Seeds rapidly take up water and swell in size. Metabolic activity resumes.

Day 4-6: Radicle Emergence

• The root (radicle) breaks through the seed coat and starts growing downwards.

Day 6-10: Hypocotyl Hook Formation

• The embryonic shoot (hypocotyl) forms a hook that pulls the cotyledons up as it grows towards the soil surface.

Day 10-14: Emergence

• Seedlings emerge from the soil. Cotyledons open and turn green. True leaves form shortly after.

Note that germination time varies among brassica species:

• Broccoli, cabbage, cauliflower seeds sprout in 5-10 days.

• Kale, collards, kohlrabi may take 7-14 days to emerge.

• Brussels sprouts are slower, germinating in 10-21 days.

Let’s look more closely at how to accelerate brassica seed germination.

Tips for Faster Germination

Here are some tips to help your brassica seeds germinate as quickly as possible:

• Select fresh seed from a reputable source and check the expiry date.

• Provide bottom heat of 65-85°F (18-29°C) using a heat mat, greenhouse or other warming method.

• Warm up refrigerated seed packets to room temperature before opening.

• Moisten soil before planting and keep consistently damp but not saturated.

• Plant at the ideal depth according to seed size. Large seeds like broccoli 1⁄2 inch deep, small seeds like cabbage just 1⁄4 inch.

• Cover seeds with vermiculite or coco coir to retain moisture, not soil which can cake and prevent emergence.

• Use a thick organic seed starting mix that holds moisture but still drains well.

• Use large cell trays or plugs so seedlings have plenty of room to grow unrestricted.

• Grow seedlings under lights or in a sunny window immediately after sprouting.

What to Do After Germination

Once those little green seed leaves (cotyledons) emerge, your brassica seedlings will start growing rapidly. Here’s how to care for them:

• Water regularly to keep the soil consistently moist but not soggy.

• Move under grow lights or into full sun. Turn/rotate plants for even growth.

• Provide adequate ventilation and air circulation.

• Keep ambient temperature around 65-70°F (18-21°C) during the day and 55-60°F (13-16°C) at night.

• After true leaves form, begin fertilizing weekly with a water-soluble vegetable fertilizer at 1⁄4 strength.

• Harden off and transplant into the garden about 3-4 weeks after germination when seedlings have 3-4 true leaves.

With the proper care, your brassica transplants will grow into healthy, productive vegetables. Just be patient, keep them watered, and let those seeds work their magic underground. In no time at all, you’ll have trays full of thriving broccoli, cabbage, cauliflower and more to plant out once the soil warms up!

Troubleshooting Poor Germination

Sometimes brassica seeds fail to sprout well or at all. Here are some common causes and solutions:

Problem: Seeds rotting in soil before germinating

Cause: Excessive moisture, poor drainage

Solution: Sow in seed starting mix, not garden soil. Improve drainage.

Problem: Seeds dried out and dying

Cause: Soil allowed to dry out

Solution: Water more frequently. Cover seeds with vermiculite to retain moisture.

Problem: Seeds germinating poorly

Cause: Old seed, improper planting depth, low soil temperature

Solution: Use fresh seed stored properly. Sow at correct depth. Provide bottom heat.

Problem: Leggy, weak seedlings

Cause: Insufficient light after germination

Solution: Move under grow lights or into full sun immediately after sprouting.

With the right conditions and care, you can count on your brassica seeds to successfully progress from seed to seedling. Just be ready to start the hardening off process as soon as the first true leaves appear!