Not many people have seen cabbages flower or go to seed because they’re harvested as soon as they mature. However, like other plants in the Brassica family (such as broccoli and cauliflower), cabbage produces seed pods, from which you can get the seeds.
You can get seed from a cabbage plant by waiting for it to go into seed. Cabbage is a biennial plant; its life cycle lasts two years. In the second year, the cabbage starts to flower after winter, where it’ll begin to grow stems, flowers, and seed pods. You can harvest the seeds when the pods dry.
In this article, I’ll discuss the process the cabbage goes through until it goes into seed, the ideal conditions, and what to expect when harvesting cabbage seeds.
Cabbage usually bolts when exposed to temperatures below 50°F (10°C) for 20 days or longer. Even when the cabbage hasn’t produced a head, it will start growing stems with flower heads once it overwinters.
You can prepare cabbage plants for seeding. Here’s how:
- Don’t harvest cabbage heads because the best seed stalks grow from the middle of the cabbage head. You should also choose the best cabbage heads if you want great seeds.
- If your region experiences severe winter, uproot the cabbage plants, ensuring you get the roots. If you experience mild winters, you don’t need to uproot the cabbage plants. (I have discussed overwintering methods below, depending on winter severity and your preference).
- If you’re storing the cabbage indoors, dampen the roots and then store the plant in a cold basement, refrigerator, or root cellar.
- Check the cabbage over time to ensure the root remains damp during the entire storage period. Remove the dry or rotting cabbage leaves.
- Disinfect the wounds with root ash to keep the rot from spreading.
- When spring rolls in, replant the cabbage. Ensure the soil is still cold during the winter season. Remove the excess soil cover for cabbages stored in the ground and leave them to grow. You don’t need to uproot them.
- Make a shallow “X” incision on the cabbage head. It should be 3-6 cm (1.2-2.4 inches) deep. The cut shouldn’t be too deep because it may interfere with the growing point found in the inner core of the cabbage. You should repeat the incision if the seed stalks take too long to emerge.
- Space the plants because once they start growing stems, they’ll take up a lot of space. The ideal spacing between the plants is 2-3 feet (61-91 cm).
- Seed stalks will start emerging from the cabbage’s center. Before long, you’ll notice flower heads as well.
- The seed pods will start growing, and they will mature over time. Leave them until the pods begin to dry.
- Harvest the dry pods and keep them in a ziplock bag for a few days.
- Crush the pods and collect the seeds in the bag.
- Sort out the seeds and store them until the next planting season.
When replanting cabbages, you must be wary of planting them alongside other plants in the brassica family. Cross-pollination may occur, interfering with the cabbage variety you hope to harvest.
You can prevent cross-pollination by doing the following:
- When it starts to flower, stake the cabbage, as the seed stalks can be heavy.
- Cover the cabbages with a net that bees can’t get through.
- In the mornings, open the nets to allow the bees to get in and cover them again. Let the bees out after a few hours and cover the cabbages again.
I use the YHmall Garden Netting (available on Amazon.com) to keep bugs from my plants, and they can still help to prevent cross-pollination. It has great size, and it’s lightweight and sturdy. The fabric is also strong enough to last the growing season, which is ideal when dealing with cabbage.
Check out: Homemade Bug Spray for Cabbage Plants
Cabbage is a cool-season vegetable that is either planted in early spring for a summer harvest or autumn-early winter for a spring harvest. Whichever cabbage variety you grow, you’ll only harvest cabbage seed in the second year of growth.
It takes a few weeks for cabbage to go into a seed after replanting in spring during the second year of its life cycle. The duration it takes will depend on the overwintering method used. Cutting the roots will take longer to seed since it will focus its energy on root growth.
By summer, the seed pods will be dry and ready for harvest. You may need to store the dry pods for at least a week for the seeds to dry before getting them out of the pods. When stored correctly, cabbage seeds can last up to 5 years.
Although cabbages grow throughout the United States, at least 78% of all cabbages come from:
- New York
California, Florida, and Texas have mild winters, while Wisconsin and New York have harsh winters.
Cabbages bolt in the second year of growth, but first, they need to get through the winter season. How you’ll overwinter cabbages in Wisconsin, whose temperatures drop to -30°F (-34°C), is different from how you would do it in California (50°F/10°C)
Besides the location and winter conditions, you should consider the following when overwintering cabbages.
- The size of the head. Smaller, firm heads will overwinter better.
- Avoid overdeveloped or split heads. When choosing the cabbage variety for seeding, you need to know if it will mature by the end of the fall. For early varieties, sow the seeds in May or June.
- Save more cabbage plants for overwintering because not all of them will survive. For example, if you save 30, you may end up with 10-15 cabbage heads.
- Overwintering is the most sensitive period of cabbage seed production. You need to choose a cabbage variety that will withstand low temperatures. You should also pick the best heads, plus those with characteristics you prefer.
- The available storage infrastructure.
Read: Holes in Cabbage Plant Leaves? [What needs to do]
There’s more than one way to overwinter cabbage plants, which is great, as you can choose which one best suits you. I’ll go over the various methods in the following sections.
The best way to overwinter cabbages in regions with extreme winter seasons, such as New York and Wisconsin, is to uproot the cabbage plant before the first frost. To do this, follow these steps:
- Remove the loose leaves until you remain with those firmly attached to the head. The cabbage head should be dry and free of soil. Any wetness will cause the leaves to start rotting.
- Store the cabbages in a cellar with an earthen floor in areas with low air humidity.
- If your area has high air humidity, hang the cabbages on a line with the head facing down. Use the air conditioner or dehumidifier to reduce the moisture in the air. Ensure the temperature in this room shouldn’t fall below 32°F (0°C)
- Check the cabbages throughout winter. Gray mold sometimes attacks the outer leaves, causing them to turn yellow and rot. Remove these leaves and treat any wounds with wood ash.
- Plant the stored cabbages 60 cm (23.6 inches) apart in spring, with only the cabbage heads above the ground.
- Make an incision on the head for the seed stalks to grow.
You can also leave cabbages to overwinter in the ground if you have a mild winter. However, you should add compost and cover the cabbage heavily with soil to protect the roots from frost. This method saves you time because you don’t need to transfer the cabbage plants.
Check out: Cabbage Leaves Turning Brown? [Causes & Cares]
The other overwintering method for areas with mild winters is to dig deep channels. Follow these steps to do so:
- Uproot the cabbage and plant it deep in the ground, slightly tilting the head.
- Space the cabbages appropriately to ensure they don’t touch one another.
- Cover the cabbage head with manure, compost, soil, or dry leaves to protect it from snow.
- Remove this covering in early spring. However, you don’t need to uproot the cabbage.
- Once you remove the excess cover, you should leave the cabbage to push up beyond the soil covering and flower.
This video shows the various overwintering methods you can use when growing cabbage for seed.
You can also overwinter the cabbage without the head. The downside is the quality of these cabbage seeds will be poorer than those that emerge from the head. The seeds will also be fewer. Follow these steps:
- Cut off the head at the end of summer because it needs to be dry before you overwinter it in the ground.
- Leave the stems to dry for several days and disinfect the head with wood ash. You can prevent rot by applying grafting wax.
- Dig a deep channel and line the cabbage stems in a row, with the head facing up.
- Cover the stalks with soil over winter.
- During spring, remove the excess dirt and allow the cabbage to grow and flower.
You can use Walter E. Clark Grafting Wax (available on Amazon.com) to protect the cut cabbage head from rot. This is a hard wax but softens when you heat it or place the container in hot water. When it cools, it’ll seal the cabbage and keep external elements from destroying it when overwintering.
Furthermore, you may like the below more gardening articles:
- Why Are My Cabbage Leaves Turning Purple?
- Why Are My Cabbage Leaves Turning Yellow?
- How To Grow Cabbage in Containers?
- The Dragon Tree: What You Need to Know About It?
- How To Save a Freezing Cabbage Plant?
To get seeds from a cabbage plant, you have to overwinter the plant and wait for it to seed. After overwintering, cabbage plants need a lot of water to allow new roots to grow. Keep watering until you notice new growth. Once it starts flowering, ensure you stake each plant because the stalks can become quite heavy.
Cabbage seeds are tiny, so you must be careful when harvesting the pods. It’s best to keep the pods in a ziplock bag and collect the seeds before disposing of the dried pods.
I’m Elsa, and I love gardening. I started GardeningElsa.com as a resource for other gardeners, and I offer expert advice on gardening topics such as plants, flowers, herbs, and vegetable gardening. On my website, I share my latest tips and tricks for creating beautiful gardens. When I’m not working on my website, you can find me in my own garden, tending to my plants and flowers. Read more about me.