Brassica tournefortii is an important broadleaf weed of the winter season in the northern grain region of Australia. Knowledge of germination ecology of this weed would help in implementing effective weed control programs. A series of experiments were conducted to study the germination and dormancy behavior of four biotypes of B. tournefortii seeds, biotypes A (collected from barley crop), B (barley fence lines), C (chickpea crop), and D (chickpea fence lines), collected from the St George region of Queensland. The aim of this research was to determine the effectiveness of various methods on the seed dormancy release of B. tournefortii. Water, potassium nitrate and a soil extract did not release dormancy in B. tournefortii seeds (biotype A) at 20/10 °C in the light/dark regime. Cold stratification (5 °C) also did not improve germination. However, gibberellic acid (GA3; 100–300 mg kg−1) stimulated germination (>88%). Germination also improved when seeds were immersed in sodium hypochlorite (NaOCl; 42 g L−1) for 10 minutes and the effect was more pronounced under the complete dark environment (89% germination at a day/night temperature of 20/10 °C). The NaOCl treatment makes seeds more porous and decreases sensitivity to light. Another experiment in light/dark conducted at 25/15 °C with two biotypes (A and D) showed that, without NaOCl treatment, biotype A was more sensitive to light (29% germination) as compared to biotype D (92% germination). Our results suggest that dormancy in B. tournefortii seeds can be broken by the combination of NaOCl (10 min) and a dark environment. A day/night temperature of 25/15 °C was found best for optimum germination (>87%) for all the biotypes (A-D) when incubated in dark after treating with NaOCl. This research indicated a high degree of variability in germination responses for various biotypes of B. tournefortii seeds to various sets of conditions, which may be due to metabolic changes in response to maternal environments or genetically controlled mechanisms. Information gained from this study will be important in developing a better understanding of the dormancy behavior of B. tournefortii seeds in response to tillage systems or maternal environments that could influence the weed seed bank in the soil and therefore help in designing suitable weed management programs.
Brassicas are a versatile group of cool season vegetables that include favorites like cabbage broccoli kale and Brussels sprouts. As a home gardener, knowing the expected brassica seed germination timeline can help you properly plan and schedule your plantings. In this article, we’ll provide a detailed overview of the brassica germination process and tips for getting your seeds to sprout quickly.
What Factors Affect Brassica Seed Germination?
Several key factors impact the speed of brassica seed germination
Soil Temperature
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Brassica seeds germinate best at soil temperatures between 65-85°F (18-29°C).
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They can sprout in soils as cool as 50°F (10°C) but germination will be slower.
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Temperatures above 85°F (29°C) can inhibit germination.
Soil Moisture
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Seeds need consistent moisture to germinate. Allow the soil to dry out slightly between waterings but don’t let it become parched.
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Excessive water can lead to damping off disease. Good drainage is important.
Seed Planting Depth
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Sow brassica seeds 1⁄4-1⁄2 inch (0.5-1 cm) deep. Any deeper delays emergence.
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Seeds must reach the soil surface to start photosynthesis.
Seed Viability
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Older seeds or poor storage conditions negatively impact germination rates and speed.
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For best results, use fresh seeds within 1-2 years of harvest.
What is the Typical Germination Timeline?
Given optimal temperature, moisture and planting depth, here is the general brassica seed germination timeline:
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 the time varies by brassica species:
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Broccoli, cabbage, cauliflower seeds sprout in 5-10 days.
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Kale, collards, kohlrabi may take 7-14 days to emerge.
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Brussels sprouts are slower, germinating in 10-21 days.
How to Accelerate Brassica Seed Germination
Here are some tips to help your brassica seeds germinate more quickly:
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Select fresh, high quality seeds from a reputable source and check the expiration date.
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Provide bottom heat between 65-85°F using a heat mat, greenhouse or other method.
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Allow refrigerated seed packets to reach room temperature before opening.
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Moisten soil before planting and keep consistently damp but not saturated.
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Plant seeds at the ideal depth based on size – large seeds like broccoli 1⁄2 inch deep, small seeds like cabbage just 1⁄4 inch.
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Cover seeds with vermiculite or coco coir to retain moisture, not soil which can cake.
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Use a thick, organic seed starting mix that holds moisture but still drains well.
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Sow seeds in large cell trays or plugs so seedlings have room to grow.
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Move under grow lights or into sun immediately after sprouting.
What to Do After Germination
Once the seed leaves emerge, brassica seedlings will start growing quickly. Here’s how to care for them:
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Water regularly to keep moist but not soggy.
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Move under grow lights or into full sun. Rotate plants for even growth.
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Provide good air circulation and ventilation.
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Maintain 65-70°F during the day, 55-60°F at night.
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Fertilize weekly at 1⁄4 strength after true leaves form.
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Harden off and transplant outdoors when seedlings have 3-4 true leaves.
With proper care, your brassica transplants will grow into productive vegetables. Be patient, keep them watered, and let the seeds work their underground magic! Soon you’ll have trays full of thriving brassicas ready 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:
Seeds Rotting in Soil Before Germinating
- Cause: Excessive moisture, poor drainage
- Solution: Use seed starting mix, not garden soil. Improve drainage.
Seeds Drying Out and Dying
- Cause: Soil allowed to dry out
- Solution: Water more frequently. Cover seeds with vermiculite.
Poor Germination Rates
- Cause: Old seed, improper planting depth, low soil temperature
- Solution: Use fresh seed stored properly. Sow at correct depth. Provide bottom heat.
Leggy, Weak Seedlings
- Cause: Insufficient light after germination
- Solution: Move under grow lights or into full sun immediately after sprouting.
Frequently Asked Questions
What month should you plant brassicas?
In cooler climates, brassicas can be grown spring through fall, avoiding the heat of summer. In hotter regions, grow them in spring or fall.
Do brassicas need heat to germinate?
They germinate best at 65-75°F but will sprout at 50°F. Use a heat mat if it’s cool. Remove once germinated.
How long does it take for brassica rapa to germinate?
Seeds should germinate within a day or two. Monitor soil moisture but avoid saturation.
What temperature do brassica seeds germinate?
65-75°F is optimal but they will germinate at temps as low as 50°F. Heat mats can help in cool conditions.
How long do brassicas take to grow?
Greens like baby kale and bok choy produce edible leaves in just a few weeks. Full size cabbages take 40-60 days to mature.
When should brassica seeds be started?
Refer to your last frost date. Start seeds so transplants are ready about 2 weeks before your average last spring frost.
How are brassicas grown?
Harvest them young and succession plant for extended harvests. Rotate planting sites and control pests to keep plants healthy.
With the right conditions, brassica seeds will progress smoothly from seed to seedling. Just be ready to start hardening off your transplants as soon as those first true leaves appear! Then you’ll have robust, cold-hardy brassica seedlings ready to thrive in your spring or fall garden.
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Brassica tournefortii Gouan. (known as wild turnip in Australia) is an important winter season broadleaf weed in the northern grain region of Australia. In Australia, it has been reported that B. tournefortii could reduce canola yield1 and other winter cereals2 through competition. This weed occupies the 6th position in the national ranking in terms of revenue loss (AU$ 10.6 million) due to crop yield losses in Australia2. Some biotypes of B. tournefortii have developed resistance to chlorsulfuron in Western Australia and South Australia3.
Weeds possess unique characteristics such as outstanding adaptability, high reproducibility, resistance to abiotic stresses and germination periodicity4. The timing of germination is an important phenomenon in a plant’s life cycle5, which depends on seed dormancy mechanisms/behavior6. Seed dormancy is the inability of seeds to germinate in a specified period under optimal environmental conditions that otherwise are favorable for their germination7. Dormancy is of two types: primary and secondary dormancy. Primary dormancy is induced during the seed development phase, resulting in dormant seeds when they disperse from the mother plant. Secondary dormancy is a result of unfavorable environmental conditions after seed dispersal8. The existence of varying dormancy mechanisms in weed seeds enables a large proportion of the weed seed bank to emerge over an extended period of time9,10. Establishment of weeds in the field is strongly related to the portion of the seed bank that has been released from dormancy10,11. Therefore, knowledge of the seed dormancy mechanism and germination behavior of B. tournefortii may lead to a better design of an efficient weed management system12.
Seed treatment with sodium hypochlorite (NaOCl) solutions is known for reducing losses in germination caused by fungus. It has been revealed that a seed treatment with NaOCl caused changes in seed metabolism that influenced germination13. However, the effects of NaOCl on germination may be positive or negative. Some authors reported that NaOCl either enhances or inhibits seed germination14,15. On the other hand, some authors reported that NaOCl inhibited the rate of germination but not the total germination16,17. These differences in results might be due to differences in the duration of treatment or concentration used18. Therefore, these studies suggest that some weed seeds require a specific immersion time in NaOCl for releasing dormancy.
Various studies have evaluated the role of NaOCl in breaking weed seed dormancy19,20,21,22. These studies indicated that germination increased with increasing lengths of exposure of weed seeds to NaOCl, but up to certain limits. The immersion of weeds seeds in NaOCl made the seeds more sensitive to the exogenous GA3 application, light, or both23. Treatment of NaOCl released seed dormancy of Avena fatua L. possibly by modifying the properties of the hull and seed coat membranes, or by increasing the permeability of the seed to oxygen22.
Seed germination is an important phenomenon because the successful establishment of weeds depends on the ability of their seeds to germinate7. Various environmental factors influence weed seed germination, for example, germination dependent upon temperature, as the emergence rate is closely correlated with soil temperatures24,25. Light is another major factor influencing seed germination. Some weeds require light for germination and others prefer darkness for germination7. Evidence related to the ability of weed seeds to germinate at various soil depths has also been widely reported26,27. The optimum environmental conditions, like temperature and light, necessary for germination vary considerably, depending on weed species28,29,30,31. A better understanding of the germination and dormancy of B. tournefortii will aid in predicting its potential behavior as it spreads into new areas of Australia. Furthermore, information on the dormancy mechanism of B. tournefortii seeds would be useful in developing effective control measures.
Successful interruption of some Brassica weed seed dormancy was recorded with various methods such as alternating day/night temperatures under light/dark and dark regimes, NaOCl, and cold stratification23,25. A previous study in Southern Australia revealed that seeds of B. tournefortii had a low dormancy immediately after harvest and seed germination was not affected by light conditions29. However, in our study, seeds collected from the St George region exhibited a very high level of dormancy when germination was performed immediately after harvesting. These results suggest that germination behavior of B. tournefortii may vary with different biotypes and maternal environments. The information on the germination ecology of B. tournefortii seeds is limited in the northern grain region of Australia. The knowledge of seed germination ecology of B. tournefortii in response to the maternal environment would help in implementing weed management strategies focusing on ecological weed control. Therefore, the aim of this research was to evaluate different methods for breaking seed dormancy of B. tournefortii collected from the northern grain region of Australia and their effect on seed germination.
Effect of light, NaOCl immersion time, and GA3
In the light/dark regime, the highest germination was 43% when seeds (biotype A) were incubated without GA3 treatment after immersion with NaOCl for 30 minutes (Table 2). With GA3 treatment, however, the highest germination (95%) was recorded for seeds that were immersed with NaOCl for 10 min. In the dark environment, seed germination without GA3 treatment was highest when incubated after immersion with NaOCl for 10 min and was similar with the germination values obtained after treating with NaOCl for 20 and 30 minutes. With GA3 treatment, seed germination remained similar (88–97%) whether soaked (up to 30 min) or not in NaOCl solution.