Brussels Sprout Plant Growth Stages | Life Cycle

If you ask me, Brussels sprout’s (Brassica oleracea var. gemmifera) bad rep is pretty undeserved! I’m a strong believer that most people who hate this green veggie just haven’t had the chance to eat well-prepared sprouts.

Fresh Brussels sprouts are the first step to creating a nutritious and delicious dish, and there’s no better way to get your hands on some than by growing them yourself. So, in my efforts to improve the public image of this vegetable, I’m going to teach you about the various Brussels sprout plant growth stages.

Conditions for Growing Brussels Sprouts

The Brussels sprout plant is a type of cole or Brassica crop, alongside its close relatives’ broccoli, cauliflower, cabbage, and kale. If you’ve grown any of these vegetables in the past, you’ll see a lot of similarities in their care.

Brussels sprouts are cool-weather vegetables that grow well in USDA zones 2 to 10. They’re often planted in late spring or summer for a fall or early winter harvest. Unlike most garden crops, sprouts actually improve in flavor when exposed to a light frost pre-harvest.

Plant Brussels sprouts outdoors in a location that receives at least 6 hours of bright sunlight per day. While adequate sunlight is needed to support good growth, temperatures over 80°F can cause stress. In warmer climates, providing temporary shade can help protect Brussels sprouts from the hottest part of the day.

The other secret ingredient to growing Brussels sprouts is moisture. According to Utah State University, you should aim for 1 to 2 inches of water per week on average. Avoid inconsistent soil moisture which can trigger misshapen or bitter sprouts. I recommend mulching around Brussels sprouts to improve moisture retention.

A pH-neutral, well-draining soil that is high in organic material is ideal. Most gardeners, including myself, prefer to amend the soil with aged compost prior to the season’s start. Continue feeding throughout the growing season with a vegetable fertilizer high in nitrogen.

Growth Stages Of Brussels Sprout

The average Brussels sprout is ready to harvest 90 to 120 days after seed germination. New sprouts will continue growing from the top of the stem until your area experiences a hard freeze or the plant bolts.

Brussels sprouts are technically biennials, meaning that they naturally require 2 years to complete a full life cycle. However, the vast majority are grown as annuals. There are many cultivars to choose from but they’re all grown for their so-called ‘sprouts’. 

Many people compare Brussels sprouts to mini cabbages, and it’s easy to see the resemblance. Others misidentify the edible sprouts as immature flower buds. To avoid any confusion, I think it’s important to explain what a Brussels sprout actually is. 

A Brussels sprout is a swollen leaf bud. All Brassicas have these leaf buds but they tend to be very small. 

These swollen buds probably don’t benefit the plant itself in any way but — many centuries ago — we humans saw the potential as a food source and have cultivated Brussels sprouts ever since. (It’s certainly not the only vegetable plant we’ve done this with!)

1. Seed Germination 

Like all vegetables, the Brussels sprout starts as a small seed. In my opinion, the seeds look a lot like peppercorns and are harvested from flowers that appear in the plant’s second year.

According to Missouri State University, the ideal temperature for Brussels sprout germination is 45 to 85°F. Viable seeds should germinate within 4 to 20 days in these conditions.

During germination, water enters the seed and triggers growth. Root development is the next thing that happens and allows the seed to access more moisture, oxygen, and nutrients from the soil. Once the root emerges, sprouting is not far behind.

2. Seedlings

After germination, Brussels sprouts seeds quickly turn into seedlings. The average Brussels sprout seedling started indoors needs to grow for about 28 days before being ready to transplant into the garden.

Brussels sprouts belong to a category of plants called dicots, meaning that they first emerge with two cotyledons. Cotyledons are simple leaves that develop inside the seed as part of germination. 

Note that these proto-leaves won’t have the same shape as mature foliage — some beginner gardeners wrongly assume that they’ve planted the wrong thing!

Over the next few weeks, the seedlings will develop their first ‘true’ leaves. This foliage will be small in size but otherwise resemble normal Brussels sprout leaves.

Brussels Sprout Seedling with First True Leaves

3. Vegetative Growth

There’s no definitive point at which Brussels sprouts exit the seedling stage. But there will definitely be a day when you visit your garden and find that your Brussels sprouts all of a sudden look like full-grown plants.

Most cultivars grow to at least 2 to 3 feet tall. Before the harvestable buds grow, a Brussels sprout plant will look like a loose head of cabbage atop a tall stalk.

The vegetative growth stage is essential to a good crop. If a Brussels sprout struggles to thrive early in the season, it won’t have the energy or structural support needed to develop healthy buds later on.

4. Bud Development

On average, harvestable Brussels sprouts (leaf buds) will begin to appear 80 to 90 days after germination or about 50 days after transplanting. These buds grow along the length of the stalk in a spiral pattern, emerging from the joints between the main stalk and existing leaves.

During this stage, it’s recommended to remove lower leaves as they begin to turn yellow, or when the emerging sprouts become crowded. 

According to the Old Farmer’s Almanac, you can also cut off the very top of the plant once the bottom one-third of the stalk has developed sprouts. This practice directs energy into further sprout development versus top growth. However, I don’t recommend cutting off the top of your Brussels sprout if you intend to harvest into wintertime.

Maturing Buds on Brussels Sprout - Brussels Sprout Plant Growth Stages
Maturing buds on Brussels Sprout stem

5. Flowering

Flowering is still a part of the Brussels sprout life cycle even if it has nothing to do with the part of the plant we eat. Home gardeners will only be interested in this stage if they plan to collect seeds for future crops.

The Brussels sprout plant produces loose clusters of small, yellow flowers near the top of the stalk.

Normally, Brussels sprouts only flower in their second growing season after surviving the winter. However, premature flowering can occur in some plants. This phenomenon is called bolting.

Bolting is often caused by fluctuating temperatures. It can also be the result of stressors — e.g., drought — that tell the plant it needs to reproduce as quickly as possible.

Flowering uses up valuable energy and can ruin the quality of any buds currently on the plant. If your Brussels sprout is showing early signs of bolting, I recommend harvesting any buds as soon as possible.

6. Pollination

Nearly all Brussels sprout varieties require cross-pollination for seed production. This can occur via insects, wind, or manual pollination.

Since all cole crops belong to a single species, it’s possible for Brussels sprouts to cross-pollinate with, say, a cabbage plant. However, this cross will not produce usable seeds. For seed production, Brussels sprout plants must be isolated from other cole crops.

7. Seed Development

After successful pollination, Brussels sprout flowers are replaced by small seed pods. Allow the pods to dry out on the plant before collection but be aware that birds or wind may carry off seeds that are left out for too long.

Brussel Sprout Timelapse Video

This plant was grown for filming purposes and a 24hr grow light cycle was used, reducing the growth timeline significantly, when compared to outdoor growth with natural light.

Growing Brussel Sprouts Plant From Seed Time Lapse (147 Days)

When To Harvest Brussels Sprouts

Begin harvesting Brussels sprouts when the buds are 1 to 2 inches in diameter. Keep in mind that the sprouts at the bottom of the plant tend to mature the earliest. Be sure to harvest these buds first. 

New buds will continue to grow near the top of the stalk as long as temperatures stay between 25 and 80°F.

FAQ Brussels Sprout Plant Growth Stages

Citations

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Ben's horticultural interest grew when graduating from Hertfordshire University in 1997. Having contributed to numerous publications including Better Homes & Gardens, Garden Design Magazine, and The English Garden. He is also the author of Propagating Houseplants Made Easy.