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Tips For Growing Broccoli from Seed

Updated: Mar 21, 2023

Broccoli is a nutrient dense food many of us want in our diet, but learning to successfully grow your own can be tricky. Don't get me wrong, the plant itself is easy to grow, it's the big beautiful crown of broccoli that can be allusive. Let's take a look at how to grow broccoli from seed.

Large head of broccoli grown in a Calgary gardening vegetable garden in zone 3.
Broccoli grown in 2022

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What Broccoli Varieties are Best for Zone 3?

When to Plant Broccoli Seeds

Covering Broccoli with Netting

The Best Soil for Growing Broccoli

When to plant Broccoli Outdoors

How Many Broccoli Plants to Grow Per Person

How Long Does it Take for Broccoli to Grow? How to Harvest.

What Broccoli Varieties are Best for Zone 3?

When looking at broccoli seeds, look for varieties with the shortest days to maturity. These broccoli varieties work best in zone 3 because we have fewer frost free growing days than warmer zones, however, our summers can be hot, causing broccoli to "bolt" (go to flower without creating a head). If your broccoli bolts, you may end up with plenty of leaves and no broccoli crown. I have had good success with Gypsy broccoli seeds.

Young broccoli plants in a tray for Calgary gardening in zone 3.
Young broccoli plants ready to be planted in the garden

When to Plant Broccoli Seeds

Start your broccoli seeds indoors the last week of March. The 6 cell trays work well for starting broccoli in. If you find your broccoli seedlings are drying out in less than a day you can transplant your seedlings into 3.5 inch pots as long as you can see good root formation at the base.

Broccoli also does well using the winter sowing method. If you choose to start your seeds this way, plant the beginning of March. Plant 5 broccoli seeds per 1 gallon milk jug.

Covering Broccoli with Netting

You will want to keep your broccoli plants covered at all times when outdoors with some kind of netting, other than when you are harvesting, weeding, and checking on your plants. Try to harvest and weed early in the morning before the moths are out. Make sure your netting has no spaces between it and the soil. Rocks or the landscaping staples shown below work well to keep it in place (until winds become too strong!). Water is able to get through the netting and you can water the plants without removing the netting.

Broccoli, cauliflower and cabbage covered with netting in a zone 3 raised garden bed in Calgary Alberta.
My covered brassica bed

I have tried two different types of netting (shown from Amazon below). The least expensive is a white "floating row cover". This type of row cover can keeps flea beetles off and also help slightly mitigate scorching sun when the weather gets too hot. The main issue is that it tears easily and can get quite ripped up in a windy storm. Even a bad hailstorm can rip through the row cover. If you choose heavier weight floating row cover, it will be more resilient, but it will cost more.

The Best Soil for Growing Broccoli

Broccoli, along with other brassicas, is a heavy feeder. Work plenty of compost into your soil prior to planting. Check out How to Improve Your Garden Soil for more tips on soil.

When to plant Broccoli Outdoors

Transplant when your outdoor temperatures are expected to be above -4 degrees C (24F). At this point your broccoli seedling should have 4 or 5 true leaves. Make sure you harden off your broccoli seedlings prior to transplanting.

Young broccoli, cauliflower and cabbage plants planted in a raised bed zone 3 vegetable garden in Calgary Alberta
Brassica bed companion planted with marigolds

How far Apart Should Broccoli Plants Be?

Plant broccoli plants 12 to 24 inches apart. I normally try to plant broccoli 18 inches apart. I don't plant in rows, as I use raised beds. I stagger the plants to leave more room for them to grow. It is amazing how quickly and how large broccoli plants grow to be. If you have limited space, broccoli might not be the most efficient use of a small space. Try kale or other greens instead to make the most of a small space.

How Many Broccoli Plants to Grow Per Person

If you want to grow enough broccoli to feed your family, plant 2 to 4 broccoli plants per person. Broccoli can be blanched and frozen for winter stir-fries or soups.

Young broccoli plants in a Calgary Alberta vegetable garden, zone 3.
Young broccoli plants in the garden

Top Tips on Growing Broccoli

  • Know your the proper time to plant and transplant for your area.

  • Plant in soil mixed well with compost as broccoli is a heavy feeder.

  • Plant broccoli seedlings 12 to 24 inches apart.

  • Keep plants well watered, but don't allow the roots to sit in pools of water.

  • Keep broccoli covered to prevent bugs and worms in you broccoli.

  • Harvest while heads are tight, before the flowers begin to open in the broccoli head.

How Long Does it Take for Broccoli to Grow?

Most broccoli varieties take anywhere from 52 to 75 days to harvest. Did you know that the edible broccoli crown is actually a cluster of flower buds for the plant? Once heads begin to form, monitor them very closely. Harvest before the beads on the heads start opening up into flowers, while it is still firm and tightly packed. The longer you wait, the looser it with become before it eventually blooms. Head are still edible at this point but they may become tough and bitter as they progress.

Once the main head is harvested, don't dig up your plant just yet! Most plants will continue to form side shoots. These are smaller size heads. The more you cut them, the more the plant will make, just progressively smaller in size. The leaves and stems of the broccoli plant are also edible.

Over ripe large broccoli crown in a garden grown in a Calgary Alberta, zone 3 vegetable garden.
This broccoli is over ripe. It should have been harvested sooner.

Companion Plants for Broccoli

Because broccoli is often attacked by cabbage worms (the larvae from white cabbage moths or butterflies also known as cabbage loopers) planting near other plants that deter moths can help protect broccoli plants. Plants that deter cabbage moths include calendula, chamomile, dill, garlic, marigolds, mint, rosemary and sage.

Other plants suitable for planting near broccoli are artichokes, beets, celery, cucumbers, nasturtiums, onions, oregano, potato, radishes and spinach.

Avoid planting near pole beans or other brassicas as they attract the same pests (unless you are able to keep covered at all times).

Cabbage, cauliflower and broccoli plants growing in a raised garden bed in a zone 3 vegetable garden in Calgary Alberta Canada.
Brassica bed in mid summer

Other Pests to Broccoli

Root maggots are another serious nemesis of plants in the brassica family. They can cause extreme destruction of even large mature plants in a short amount of time. The black flies look like a smaller version of a house fly and lay their eggs around the base of the plants. Once the tiny white larva hatch and the base of the plant, they bury down and eat away at the root system. Even a large healthy plant can be toppled in a matter of days. Keeping plants covered with a fine netting can help block the flies. If you see small black flies around your plants, inspect the base of the plant for tiny egg clusters that may be removed before the larva hatch.

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