Growing broccoli from seed can be a bit challenging for beginners, but it’s not difficult once you learn how.
In this complete guide, I will give you all the information you need about how to grow broccoli seeds successfully, even if you’ve struggled with it in the past.
You will learn the best sowing methods to use, when to start, step-by-step planting instructions, plus seedling germination time, identification, care, repotting, transplanting, and more.
Growing Broccoli From Seed
| Days to germination | 5-10 days |
| When to start indoors | 4-6 weeks before transplanting |
| When to sow outside | 3-6 weeks before your last spring frost date |
| Days to maturity | 50-90 days (depending on the type) |
| Sun exposure | Full sun |
| Seed planting depth | ⅛ – ¼” deep |
| Spacing | 12-24″ apart |
| Soil temperature | 60-80°F |
Types To Grow
There are several different varieties of broccoli seeds that you can plant. Some types have larger heads, while others are small, but more prolific, or they mature earlier.
A few of my favorites are Di Cicco (classic heirloom), Early Heading (early to mature), Long Harvest (blend of early and late), Summer Purple (larger heads), Santee F1 Purple (small, but abundant).
Related Post: How To Care For Broccoli Plants
How Long From Seed To Harvest?
Many types of broccoli need a fairly long growing season to mature from seed to harvest, but some are much faster. Depending on the variety, it can take anywhere from 50-90 days.
That is a wide range, so it’s best to check the packet so you know what to expect from the specific variety you’re going to plant.
Tips For Planting Broccoli Seeds
You don’t need to do anything special to prepare your broccoli seeds before you sow them, but it’s important to plan ahead. Below I’ll talk about the different techniques you can use and when to start.
Broccoli Seed Starting Methods
There are 2 methods that you can use to grow your broccoli seeds: 1. starting them indoors, 2. direct sowing. The best one to use depends on where you live.
- Starting them indoors – If you’re in a cold climate with short summers like I am, then it’s best to start them indoors. Otherwise the plants might not have time to mature before fall.
- Direct sowing – But if you live in a warmer region, you can sow them directly into the garden, or you could try winter sowing them.
Related Post: 3 Seed Starting Methods That Every Gardener Should Try
When To Plant Broccoli Seeds
Start your broccoli seeds indoors 4-6 weeks before your average last frost date, or direct sow them as soon as the soil is workable in your garden in early spring.
They are cold hardy, and the seedlings won’t be harmed by a late frost. If you have mild winters, then you can sow them in the fall.
How To Plant Broccoli Seeds Step-By-Step
Though you will need a few things to start your broccoli seeds indoors, you don’t need to buy a ton of fancy equipment. Below is a list of what you need and the steps for sowing them.
Supplies Needed:
- Broccoli seeds
- Seedling flat with a lid
- Pre-moistened seed starting soil or peat pellets
- Water
- Hand trowel
- Heat mat (optional)
Step 1: Fill the trays – Fill your planting tray with a high quality seed starting mix, or use pre-moistened peat pellets if you prefer.
Step 2: Decide how many seeds to plant – If you’re using brand new seeds, then you can just plant one per hole. Otherwise, if they are old, then you may want to use 2-3 per hole.
Step 3: Plant your seeds – You can either make a shallow hole in the soil, and drop a broccoli seed into it. Or place the seed on top, and then gently press it into the soil. I find it easier to make the holes first.
Step 4: Bury the seeds – Lightly bury them, and gently press the soil down to ensure it comes into contact with the seeds. Since they are so small, you should only plant them about 1/8″ – 1/4″ deep.
Step 5: Add water – It’s best to water your trays from the bottom, so you don’t disturb the soil or displace the seeds. Simply pour water into the tray, and allow the soil to soak it up from the bottom. Dump out any that hasn’t been absorbed after 20 minutes.
Step 6: Cover the tray – Place the plastic lid on the top of the tray to ensure the soil doesn’t dry out during germination. Then move it in a warm location, or put it on top of a heat mat.
Broccoli Seed Germination Time
On average it takes about 5-10 days for broccoli seeds to germinate and for the seedlings to start popping out of the soil.
If you planted them indoors, and you want them to germinate faster, put the trays on a heat mat to speed things up.
What Do Broccoli Seedlings Look Like?
When they first sprout, baby broccoli seedlings will have only two leaves. Those are called “seed leaves”, and they look like two fat hearts on either side of the stem.
All of the ones that grow after that are called the “true leaves”, and those look like tiny mature ones. They usually start to form within a few days after the seed leaves have opened.
How To Care For Broccoli Seedlings
Once your seeds have sprouted, it’s important to give your broccoli seedlings the proper care so they will grow strong and healthy. Below I’ve included some detailed tips. You can also learn more about general seedling care here.
Light
Broccoli seedlings need a lot of light, or they will quickly stretch and grow leggy. A sunny window isn’t going to be enough for them.
So add a grow light and hang it a few inches above your trays at all times. Then use an outlet timer to automatically run them for 14-16 hours per day.
Related Post: A Beginner’s Guide To Grow Lights For Seedlings
Water
They won’t grow well if the soil is too dry or wet, and improper watering can lead to problems down the road. You should keep it evenly moist, but never wet or saturated.
So check daily, and add more water as necessary. A moisture gauge can help you get it right.
Air Circulation
After most of the seeds in the tray germinate, it’s a good idea to give them some fresh air. This will help prevent mold growth, and strengthen the seedlings.
Start by propping the lid open for a few days, then eventually removing it all together. Just be mindful that once the lid is off, the soil will dry out faster. So check often to make sure it’s not drying out too much.
Fertilizer
Broccoli plants are heavy feeders, so fertilizing your seedlings is very important. Once they have a few sets of true leaves, start giving them a weak dose of an organic option, like liquid compost tea.
Once you move them outside, you can use fish emulsion or liquid kelp. The seedlings absolutely love these, but they can get a little stinky when you use them indoors.
Thinning
If you planted more than one broccoli seed per cell or pellet, or you sowed them too close together, then you’ll need to thin your seedlings after they start growing.
Otherwise they’ll crowd each other out, which will stunt their growth and prevent head formation. So, once they’re a few inches tall, choose the strongest one, and thin the rest.
Potting Up
When they are twice as tall as the tray, you should repot your broccoli seedlings into larger containers. That way they will have plenty of room to grow.
I like to use plantable pots to make transplanting them easier. But you could use small plastic nursery pots instead, if you prefer. They are reusable, which is nice.
Transplanting
Broccoli is frost hardy, so you can transplant the seedlings into your garden 2-4 weeks before your average last frost date in the spring. If that makes you too nervous, then you can wait until after all chance of frost is gone.
But before you even think about planting them into your garden, you must harden the seedlings off to prepare them for life outside. Do not skip this step, or they may not survive.
FAQs
When broccoli seeds fail to germinate, either they were too old, or it was too wet or dry for them. They germinate best when the soil is 60-80°F, so use a thermometer probe. If they’re more than 2 years old, plant 2-3 per hole and thin them later.
You don’t need to soak your broccoli seeds before planting them, but it can help them germinate faster and more reliably. If you want to try it, simply soak them in warm water overnight before sowing them.
Adding bottom heat is a great way to speed up germination. Simply place the trays on top of a heat mat, and monitor the temperature with a soil thermometer. Ideally it should be between 60-80°F for the quickest germination time.
No, broccoli seeds do not need light to germinate.
Growing broccoli from seed is so rewarding, and fun too. Once you get the hang of it, it’s also very easy. Plus, you can grow some pretty cool varieties that you can’t find at the garden center.
If you’re tired of struggling, and want to learn how to grow any plant you want from seed, then enroll in my online Seed Starting Course. It’s a wonderful, fun, self-paced course that will teach you everything you need to know to easily grow your own seedlings. Enroll and get started today!
Or, if you just need a refresher, then my Starting Seeds Indoors eBook is for you! It’s a quick-start guide that will get you planting seeds in no time.
Share your best tips for growing broccoli from seed in the comments section below.
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