How to Grow Broccoli From Seed
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Broccoli is probably my very favourite vegetable of all. Naturally, when it comes to growing vegetables, our broccoli plants tend to take up a fair amount of “real estate” in our garden (especially given that they grow quite large).
But it’s totally worth it to have fresh broccoli at the height of summer, another crop that lasts well into the fall, a few freezer bags full to last the year and, as an added bonus, we eat the broccoli leaves too! And of course, whatever’s left over goes into the compost.
No part of our broccoli plants go to waste, and every year we grow more and more. In fact, broccoli was one of the first vegetables we ever grew at home in our very first garden, and we’ve grown it every year since.
We’ve also been lucky enough to have always had success growing broccoli and we’ve actually found it to be one of the easier plants to grow from seed. But I’ve heard enough other people say that they’ve struggled with growing broccoli to know that it can be a bit finicky. So I figured it would be a great candidate for our seed starting series!
Be sure to check out part one of this year’s seed starting series too!
Alright, let’s dive in…
How to Start Broccoli Seeds Indoors
- For a summer crop, start broccoli seeds indoors 4-6 weeks before your average last frost date.
- For a fall crop, start broccoli seeds indoors in late May or early June for a September or October harvest.
- Sow seeds ⅛ of an inch to ¼ of an inch deep.
- Seeds should germinate in about 5 to 10 days.
- Plant one seed per pot or to guarantee better germination, plant 2 or 3 seeds per pot and thin the seedlings out to just one per pot as they start to grow.
- Keep soil watered evenly but not sopping wet.
- Use indoor grow lights if possible to give broccoli seedlings lots of light and keep them from getting tall and “leggy” (aka. spindly).
Broccoli is a great summer or fall crop. Since it’s cold hardy, it will last in the garden well into October in most climates. That being said, you’ll need to start seeds at different times in order to get a harvest at different times.
For a summer crop, start broccoli seeds indoors 4-6 weeks before your last frost date. For a fall crop, start indoors in late May or early June for a September or October harvest.
Sow seeds ⅛ inch to ¼ inch deep. The general rule is to sow seeds about 2x deeper than the seeds are large. Since broccoli seeds are pretty tiny, they should be sown pretty shallow. But make sure they’re covered with soil. You can sow one seed per pot or sow multiple seeds for better germination rates. Two or three seeds per pot should ensure good germination. But you’ll have to thin seedlings out to one per pot when they begin to grow. We use these peat pots to start our seeds. These are great because they biodegrade in the soil so you don’t have to disturb plant roots by taking the seedlings out of the pots to transplant them.
Keep the soil moist at all times but don’t overwater. You’ll also want to keep your broccoli seedlings under grow lights as they require lots of light to grow strong and healthy. Try to keep the lights hanging just a few inches above the seedlings. If the lights are too far away (or if you keep your seedlings by a window and they need to stretch to reach the light), your broccoli seedlings could end up shooting up quite tall and getting long and spindly. Try to avoid this by growing them under grow lights. You can purchase grow lights from the store or make your own indoor grow light stand.
When it comes to starting broccoli from seed, you can technically direct sow seeds right into your garden if you live in a warmer climate. But germination and survival rates tend to be much better when seeds are started indoors and growing conditions are monitored and controlled for the first few weeks. I have a hunch this may be why some people struggle with growing broccoli.
We tried starting our fall crop outdoors last year and didn’t have any seeds germinate! The soil kept drying out too quickly and the temperature fluctuated a bit much from day to night. I don’t know for sure, but I think this may have been why we struggled with that particular crop. We’ve always had success starting seeds indoors though, and that’s the generally recommended “best practice” when it comes to growing broccoli from seed.
Transplanting Broccoli Seedlings Outdoors
- Transplant broccoli seedlings outdoors once they have 6 to 8 sets of true leaves.
- Harden them off for 3 or 4 days before transplanting them permanently into the garden.
- Do not plant in the same area where you grew broccoli or any other brassicas last season. If possible, plant broccoli where you grew peas or beans last season as the soil will have more nitrogen from the peas and beans which will help broccoli grow strong and healthy.
- For best results, fertilize the soil before planting with composted manure or organic fertilizer.
- Plant seedlings 18-24” apart (45-60cm apart) in rows 30-36” apart (75-90cm apart).
Wait to transplant broccoli outdoors until each plant has roughly 6 to 8 sets of true leaves. Harden them off over the course of about 3 or 4 days by putting seedlings outdoors for a couple hours and then bringing them back inside, then put them out for a little longer the next day and bring them back in, then put them out and leave them out in their pots overnight before transplanting them into the garden.
This is how we always harden our plants off and I notice they get visibly larger and stronger (with thicker stems) over the course of those few days when we’re hardening them off.
Be sure not to plant broccoli in the sae spot as you planted any brassicas last season. Brassicas (ie. broccoli, cauliflower, cabbage, brussels sprouts, kale, collard greens, etc.) are heavy feeders, which means they tend to deplete the soil of nutrients. So don’t plant them in the same spot as you planted them the previous season because the soil won’t be as rich and healthy as it should be to grow strong healthy broccoli plants.
If possible, try to rotate them to a spot where you grew either peas or beans the previous season, or where you previously planted a cover crop of legumes like clover. Legumes actually add nitrogen back into the soil which helps improve the nutrient content.
Still, you should add some organic fertilizer to give your broccoli the best chance. Before planting, spread some composted manure or simply some compost, or add some fertilizer to the soil where you’ll be planting. Add about ¼ cup of organic fertilizer to each planting area and mix well into the top soil.
Plant seedlings about 18-24” apart in rows about 30-36” apart. Full grown broccoli plants grow quite large and their leaves need room to spread out, so be sure to give them enough space. Make sure their roots are below the soil and then mound a little extra soil around the base of each plant to keep them well supported.
Caring for Broccoli Plants
- Grow broccoli in a location with full sun. While they are cold-hardy, they love the sun and don’t do well in the shade.
- Keep soil evenly watered but don’t let the soil become sopping wet. Make sure to plant in a well-drained area. The top 6 inches or so of the soil should be kept moist at all times (as much as possible anyway).
- Fertilize again about a month after planting. Simply spread a little rotted compost or manure or some store-bought organic fertilizer on the soil around your plants and water it in.
- Harvest broccoli heads once they have fully developed but the buds are still closed tight. Cut the head off with about 5 or 6 inches of the stem too.
- Leave the plants in the ground after you’ve removed the heads. The plants will produce offshoots of little broccoli heads giving you an extra harvest. You can also harvest and eat the leaves!
- Once you’ve harvested all your broccoli and it’s finished for the season, pull plants out by the root, mulch up and compost. Add some compost to the area to add nutrients back into the soil before planting anything else.
Broccoli is a bit of a dichotomy. It’s a cold-hardy plant that thrives in cooler temperatures but it’s also a sun-loving plant that hates shade. Plant seedlings in a location that gets full sun.
Make sure to water daily to keep at least the top 6 inches of the soil constantly moist. Try to water in the early morning or evening to keep the water from evaporating too quickly (as it tends to do midday in the summer).
To encourage strong, healthy growth, fertilize again about a month after planting by spreading some rotted compost or manure over the soil and watering it in. Do not mix it into the soil ad you could break or disrupt the roots.
Harvest broccoli heads when they are full grown but the buds are still tightly closed. If they’ve begun to open up, the broccoli is still edible but not quite as good. Once the broccoli begins to flower though, it’s too late. Keep an eye on broccoli plants in the middle of summer because they tend to bolt and go to seed quickly if you get a heat wave. Try to stay on top of them and harvest before this happens.
Once you’ve harvested the main head, leave the plants in the ground and continue watering for a couple more weeks. Removing the head encourages the plants to grow offshoots (little miniature heads of broccoli that grow off the sides of the main stem) which means an extra harvest for you!
Also, don’t waste the leaves! Broccoli leaves are edible too and taste just like broccoli but are more like kale or collard greens in nature. Add them to soups, stews and stir fries or make some Cream of Broccoli Leaf Soup!
Pull plants out by their roots, mulch them up and add to your compost once you’ve harvested all you can from them. Then add some finished compost or fertilizer to the area where they were planted to add nutrients back into the soil.
For a quick reference guide, don’t forget to grab your FREE Seed Starting Cheat Sheet. It includes at-a-glance info on exactly when and how to start 10 common garden vegetables from seed.
Wishing you homemade, homegrown, homestead happiness 🙂
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