Growing Broccoli From Seed: How to Sow, Transplant, and More (2024)

Broccoli is one of my favorite crops to grow. Not only is it high in fiber and vitamins, but it’s surprisingly easy to cultivate in a home garden. With a modest amount of effort, you can save yourself lots of money by growing broccoli from seed, rather than relying on transplants purchased from your local garden center. In this article, I’ll discuss everything you need to know when it comes to growing broccoli from seed, including sowing, transplanting, and care advice.

Why grow broccoli from seeds?

Broccoli plants are the same species of plant (Brassica oleracea) as many other brassicas (also called cole crops), including cauliflower, kale, cabbage, and Brussels sprouts. Over many generations, the original Brassica oleracea has been selected for various traits, giving us an array of different vegetables with very different appearances. Broccoli is among the most popular, and there are many benefits to growing it from seed.

• The most obvious benefit of growing broccoli from seed is the cost savings. For a $4.00 packet of seeds, you can get hundreds of plants when starting your own from seed. That same $4.00 at the nursery will get you between 1 and 4 plants, depending on where you live. That’s a big difference.
• Another benefit of starting broccoli seeds yourself are the number of varieties available. Believe it or not, there are several dozen different varieties of broccoli, each with its own flavor, level of vigor, growth habit, and maturity rate. Most nurseries only carry 1 or 2 different varieties, but when growing broccoli from seed, you can try so many others!
• A third benefit is your ability to control the way your plants are grown from day one. If you’re an organic gardener, you’ll know your broccoli plants were not exposed to pesticides, fungicides, or synthetic fertilizers if you grow them yourself.
• The fourth and final reason to grow broccoli from seed is so you can manage the timing perfectly. Broccoli is a cool-weather crop. If your nursery doesn’t have plants at the correct time of year for planting, then your harvest could suffer. Let’s talk next about the importance of getting the timing right when it comes to planting broccoli from seed.

Why good timing matters

Before you sow any broccoli seeds, it’s important to understand how to properly time the process. If you start your seeds too early, you’ll end up with leggy seedlings that may become floppy, weak adult plants. If you start the seeds too late, the plants will languish in the hot summer weather. Remember, broccoli loves cool weather, so the best time to grow it is in the spring (the fall is another choice I’ll mention later).

When to start growing broccoli from seed

To figure out the best day to sow broccoli seeds when starting from seed no matter what growing zone you live in, you’ll need to do some counting. Follow this easy plan for spring growing:

1. Start by looking at the seed packet for the number of days to maturity. Most varieties of broccoli are ready to harvest between 90 and 110 days after planting from seed. Once you’ve found that number on the seed packet, add 10 days to it to account for how long it takes the seeds to germinate.
2. Approximate the date when the daily temperature where you live hits an average of about 82°F.
3. Turn your calendar to that date and then subtract the total number of required growing days from it (days to maturity + 10 days for germination). That’s the day you should plant broccoli seeds.

Here in Pennsylvania, we typically hit an average of 82°F sometime between June 1st and June 15th. If I’m growing a broccoli variety that takes 90 days to mature (including germination time), then I should start the seeds in the last week of February or the first week of March. For those who live in a warmer climate, you may have to grow your broccoli in the winter since spring temperatures can quickly reach an average of 82°F. Residents of a colder climate, will be starting seeds later. Another tip: if you’re using an older packet of seeds, here’s how to test for viability before sowing the seeds.

The best soil to use when growing broccoli from seed

Begin sowing broccoli seeds by gathering the correct materials. Start with high-quality organic potting soil formulated specifically for seed starting. This kind of lightweight potting mix is ideal for starting seeds. It is well draining and well aerated. If you prefer to mix your own seed starting potting soil, you’ll find our favorite DIY potting soil recipes in this article.

Which containers are best for starting broccoli seeds

You can use almost any container to start broccoli seeds. Toilet paper tubes with one end folded in on itself, peat pellets, nursery six- or four-packs, and repurposed containers like yogurt cups and takeout containers all work. Whatever you choose to use, make sure it is clean and has a drainage hole in the bottom.

Do you need grow lights when growing broccoli from seed?

When possible, I recommend growing broccoli from seed under grow lights. The result is healthy, lush plants with green foliage and sturdy stems. It is possible to start broccoli seeds on a sunny windowsill, but you’ll have to carefully turn the containers a quarter turn every day to ensure all sides of the seedlings receive enough light and they don’t lean heavily to one side or another. You’ll find more information on the pros and cons of using grow lights vs a sunny windowsill for seed starting here.

If you have your broccoli seedlings under grow lights, leave them on for 14-18 hours per day. Florescent and classic grow lights should be kept 2 to 3 inches above the plant tops (raise them as your seedlings grow). LED grow lights don’t have to be quite as close to the plants. 6 to 8 inches will suffice.

Step by step instructions for sowing broccoli seeds

Here is the best technique to use to plant broccoli seeds indoors.

1. Fill your container with seed starting mix. Tap the base on a hard surface to settle the soil. The container should be filled up to the top rim. Do not press down on the soil.
2. Poke a small hole where you plan to plant each seed if the container has compartments. I use a pencil or a small dibble for this job. The hole should be about 1/4 to 1/2 inch deep. Don’t plant broccoli seeds any deeper or they may not germinate. Fill the hole back in. Alternatively, you can broadcast an entire packet of seeds across the soil surface if the container does not have individual planting compartments. Then cover the seeds with a 1/2 inch of more potting soil.
3. Water the seeds in using a fine sprinkling of water from a watering can or sink sprayer.
4. Label the container with the name of the variety and the date the seeds were planted.
5. Cover the container with a plastic dome or a sheet of plastic wrap to keep the humidity high until the seeds start to germinate. The containers don’t have to be under grow lights until the seeds germinate, but I find it easier to put them under the grow lights right away.

How long does it take broccoli seeds to germinate?

Broccoli seeds germinate in about 7 to 10 days. Unlike when you sow seeds of tomatoes, peppers, and other warm-season crops, you don’t have to use a heated grow mat to get the warm soil that encourages good germination. Broccoli seeds germinate in cool soil without any problem. Yes, a heat mat will speed the process by a day or two, but it isn’t necessary.

As soon as the first few seeds germinate, remove the dome or plastic wrap over the containers. Otherwise, mold could develop.

How to water young broccoli plants

When growing broccoli from seed, one of the keys to success is to provide the seedlings with the correct level of moisture. When the surface of the soil is dry to the touch and lighter in color, it’s time to water. You can also lift the container to see how heavy it is. Dry soil weighs less than moist soil. How quickly the soil dries out depends on how warm your home is, how big the containers are, and what brand of potting soil you used. Also, the older the plants are, the more water they require.

Fertilizing broccoli seedlings

Most seed-starting mixes do not have high fertility. In fact, most don’t have any fertilizer at all. This is to avoid burning the new roots of tender seedlings. But, as soon as your seedlings have developed their first sets of true leaves, it’s time to start fertilizing. The first set of leaves to emerge from a seed are known as the “seed leaves” or the cotyledons. The second set of leaves are the “true leaves.” As soon as they appear, it’s time to being fertilizing your seedlings every two weeks.

Use a liquid organic fertilizer or kelp emulsion mixed with your irrigation water at half of the strength recommended on the fertilizer’s label. This type of fertilization provides very low amounts of nitrogen, potassium, and phosphorus, which is really all the young seedlings need at this point in their growth.

When to transplant broccoli grown from seed into bigger pots

When the seedlings have started to develop their second set of true leaves, you can transplant them into bigger pots if you’d like. Some gardeners skip this step, but I find this potting-up to result in sturdier plants. The transplanting process encourages thicker stems and a bigger central head of mature broccoli.

When transplanting, use a standard potting mix (not a seed starting mix) and make sure the new containers also have drainage holes in the bottom. If you sowed your seeds all together in a single container without compartments, you’ll definitely want to separate them carefully and transplant each broccoli seedling into its own container. If you started the seeds in peat pellets, skip the transplanting process.

Keep the broccoli transplants under the grow lights and continue to regularly water and fertilize them.

Hardening off broccoli transplants

When the seedlings are about 6 weeks old, it’s time to prepare them for life in the garden. If you’ve timed your broccoli seed starting correctly, this should be a few weeks before your last spring frost date. The process of slowly acclimating your broccoli plants to outdoor growing conditions is known as hardening off and it takes about two weeks. Here in Pennsylvania, I start to harden off my broccoli plants in early April.

Don’t skip this step when growing broccoli from seed. If you do, your plants will suffer. To harden off seedlings, move the plants outdoors for a few hours every day, gradually increasing the amount of time they spend outdoors and the amount of full sun they are exposed to each day. Keep them properly watered throughout the process. In two weeks, they should be outside full-time, both day and night. Now your broccoli plants are ready to be planted into the garden.

How to transplant broccoli plants out into the garden

Choose a garden site with full sun. Add some compost or well-aged manure to the site before planting broccoli plants. The ideal soil pH is between 6.0 and 6.5 (you can learn more about testing for and adjusting soil pH in this article).

Transplant your broccoli seedlings to the same soil depth they were in their containers. Do not bury them any more deeply. Water immediately after transplanting.

Once they are fully hardened off, broccoli transplants tolerate frosts without issue, but I protect my plants for the first few weeks by covering them with a bottomless milk jug with the cap removed, or with a layer of floating row cover or a mini hoop tunnel. It is not necessary, but it does provide them with an extra layer of protection. And it can also help protect them from many common broccoli pests.

What to do after transplanting broccoli starts

After transplanting, mulch broccoli plants with a 1- to 2-inch-thick layer of straw, untreated grass clippings, shredded leaves, or another organic material. This keeps the soil insulated and moist.

Within a few weeks, the center of your broccoli plants will develop a small bud that will turn into a central head of broccoli. Harvest broccoli with a sharp knife while the buds are still tight, well before they open into the mature yellow flowers.

More tips for growing broccoli from seed

• Most varieties of broccoli form side shoots after the main head is harvested. Don’t pull the plants out after the first harvest and you’ll be picking side shoots until the weather gets too hot.
• For a fall crop of broccoli, start seeds indoors in July or early August for harvests in September, October, and even November. Follow the steps above and protect the plants with a layer of floating row cover or a mini hoop tunnel (more on how to use hoop tunnels here).
• Pests are often problematic regardless of whether you’re growing broccoli from seed or from purchased transplants. Handpick cabbage loopers and cabbage worms. Or better yet, grow the plants under floating row cover so the pests can’t access the foliage.
• Companion plants with small flowers, such as dill, chamomile, and cilantro, attract and support many of the beneficial insects that prey on common pests of broccoli. Plant lots of these plants in and around your broccoli crop.
• Keep your plants free of weeds by hand-pulling and mulching.
• Here’s more about when to harvest the broccoli heads from your plants
• When your broccoli is finished producing for the season and you pull out the plants, succession plant. Plant a secondary crop of beans or tomatoes. This enables you to grow two crops in the same space, increasing your yield.

Growing broccoli from seed is not only a great way to save money, it’s also fun and easy. For a few dollars’ worth of seeds, you can fill your fridge and freezer with enough homegrown broccoli to last an entire year.

For more information on growing brassicas in your garden, visit these articles:

• Organic control of cabbageworms
• How to grow Brussels sprouts
• Growing cabbage in a home garden
• How to grow kale indoors
• Growing kale outdoors in winter
• Lacinato kale

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