The Ultimate Guide: Growing Brussels Sprouts in Any Climate

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Brussels sprouts (Brassica oleracea var. gemmifera) are small heads of mini cabbages grown on the stalk of a tall, leafy plant. Brassica oleracea (wild cabbage) is also the parent plant of broccoli (italica), cabbage (capitata), cauliflower (botrytis), kale (acephala), and kohlrabi (gongylodes).

Growing Brussels Sprouts

Your Brussels sprouts’ growth depends, first and foremost, on generics and, secondly, on its environment. Any vegetable has two growth regions: above-ground foliage and below-ground roots.

Each region has five essential factors contributing to the plant’s health, resilience, and productivity.

Above-Ground Growth Factors

1. Light quality, quantity, and duration

2. Ambient temperatures

3. Ambient Humidity

4. CO2 Levels

5. Air Circulation Efficiency

Below-Ground Growth Factors

1. Soil Biodiversity

2. Water (Moisture availability)

3. Soil Oxygen Levels (6%)

4. Soil Temperature

5. Soil Fertility

Brussels Sprouts – How to Grow

I will refer to the ten growth factors above and explore their respective roles in growing Brussels sprouts. The management regime of Brussels sprout crops is listed on EPA under Group 5: Cole Crops and Brassica Leafy Greens.

As mentioned above, 11 factors influence a plant’s health, resilience, and productivity; the ten above and the plant’s specific genetics. 

We also noted that Brussels Sprouts and several other plants from the Brassica family are hybrids of the wild cabbage (Brassica oleracea). As we’ll see later, there are several Brussels sprout varieties.

Look at the ten non-genetic factors for healthy Brussels sprout growth – five above ground and five below. 

Light

All vegetables are photoautotrophs, generating their food via photosynthesis using water, CO₂, and light energy. The Brussels sprouts we eat are wrapped balls of leaves, so the plant relies on the larger collard-like leaves for photosynthesis.

Light is particular (composed of particles called photons) and travels in waves of different lengths (frequency). Human visible light spans the 380 to 750 nanometers range – blue to red. 

At either side of our visible light spectrum (blue to red), we have ultraviolet (UV) and infrared (deep red) used by plants and insects in addition to what we see.

Photosynthetic Photon Flux Density 

Light is measured in bundles called mole (mol) containing 6.22 x 10²³ photons (a standard used to reduce atomic-sized particles to a unit) or micromol (6.22 x 10¹⁷). PPFD (Photosynthetic photon flux density) is the number of usable photons reaching a plant.

Brussels sprout plants require a PPFD of 200 µMol/m²/s (100 micromols per square meter per second) in their seedling stage and 200 to 350 µMol/m²/s as they mature. Fruiting vegetables (tomatoes, peppers, okra, cucumber) need twice that.

Although Brussels sprouts are a cool season crop, extending light levels to 16 hours a day can increase yields by 30%. A better light quality (full spectrum) improves the Brussels sprout’s leaf color and resilience.

For optimal growth, Brussels sprouts need full sun. Though they will ensure some shade, it will slow the growth rate and time to maturity. Brussels sprouts already have a fairly long growing season, so you don’t want to extend it by low-light conditions.

Light and Resilience

The more effective the photosynthesis process is in producing sugars, the more abundant the resources available for other synthesis processes, including lipids (fats), amino acids (protein), and hormone production.

Plants with effective photosynthesis, a product of light, CO₂, and water, the more resilient the plant is to natural challenges, including pests and diseases. Light is essential, but root health is also responsible for water supply. 

Ambient Temperatures

All the brassica plants (including Brussels sprouts) are cool-season crops and bolt if exposed to higher temperatures. Brussels sprouts plants manage fluctuating ambient temperatures better if the soil temperatures remain stable.

If you live where spring temperatures may spike above 80°F/27°C, consider covering your Brussels sprout plants with shade cloth. It’s easier to do if you’re using row covers.

Cold temperatures trigger a higher sugar content in Brussels sprouts plants that function as antifreeze in the cells, protecting them from damage. An increase in sugars also improves the flavor.

When to Plant Brussels Sprouts

To expand your harvest window, plant several Brussels sprouts varieties with different maturity dates simultaneously and harvest in succession. 

To harvest Brussels sprouts earlier, plant less cold-tolerant varieties, known for growing faster for later (winter) harvest, and plant Brussels sprouts that are cold-hardy (slower-growing).

By planting different varieties simultaneously, you can harvest sprouts over several months, both early and late winter harvest. Harvesting Brussels sprouts after a light frost improves the taste.

Brussel sprouts prefer cool weather (below 85°F/29°F), but the full sun. This is manageable in most regions, with some challenges in late summer. Hot weather will cause most cool-season plants to bolt.

Ambient Humidity Needs for Brussels Sprouts

The humidity your Brussels sprouts can endure depends on the airflow around the plants. See the Air Circulation topic below.

Carbon Dioxide (CO₂) Levels

Carbon dioxide plays a key role in photosynthesis. Localized CO₂ levels can be boosted by adding compost to the soil, releasing CO₂ from carbon decomposition. 

The Earth’s atmosphere consists mainly of Nitrogen (87%) and Oxygen (21%). The remaining 2% contains other gasses, mainly Argon (0.9%). Carbon dioxide only represents 0.04%.

Several intensive growers pipe CO₂ to plants to increase photosynthesis efficiencies, boosting plant growth. You don’t need to do that if you grow Brussels sprouts in organically rich, biota-abundant soil.

As the microorganisms break carbon matter down, they release CO₂ and water. Have you noticed how fungus gnats fly into your face? 

They’re following the CO₂ you exhale because evolution has taught them that high CO₂ levels indicate carbon decay, a great place to lay their eggs.

The Effect of Ethylene on Brussels Sprouts

While we’re reviewing the effect of gasses on Brussels sprouts, let’s consider the gas plants release as they ripen, ethylene.

While using ripe bananas to trigger avocado ripening is a great trick, placing Brussels sprouts with ripe fruit will cause yellowing leaves.

Air Circulation

Your Brussels sprouts plants must have air movement about them. This applies to all the cabbage family plants. As brussel sprout plants respire CO₂, they release moisture. 

Respiration is the opposite process of photosynthesis and facilitates other synthesis processes.

The released moisture in transpiration and respiration builds up around the leaves, requiring air movement to prevent moisture from blocking photosynthesis. Excessive leaf moisture allows several pathogens to flourish.

Wet Leaf Risks

Wet leaf-related cole and brassica greens plant diseases include bottom rot, white mold, and wire stem.  

Plant Brussels sprouts a foot-and-a-half to two feet apart (30 to 45 cm) in rows that are minimally three feet (91 cm) apart. 

Grow Brussels Sprouts – A Winning Tip

By removing the apical meristem (the top growing point) from your growing Brussels sprouts plant, you force lateral growth. 

When the first Brussels sprouts are about half their full size, remove the apical meristem to speed up the development of the remaining buds. Timing is important as you need a sufficiently long stem for reasonable production qualities.

Grow Brussels Sprouts in Biodiverse Soil

Scientists are constantly discovering the magnificence and importance of having a diverse population of soil biomes in vegetable gardens.

The role of microorganisms in managing water and nutrient availability and improving plant resilience and disease control is beyond speculation.

Biodiversity and Brussels Sprouts Health

Compost is the best way to introduce beneficial microorganisms into gardens and an effective way to maximize plant health and resilience.

My book on composting explains all the benefits a diverse population of microorganisms offers. I am convinced that the best skill a gardener can develop is making healthy compost.

Dirt is dead, but the soil is alive, hosts life, and allows plants, including Brussels sprouts, to grow to their maximum potential. Healthy soil grows healthy plants. Full stop.

Brussels Sprouts as a Bio-Fumigant

According to Cornell University, brassica cover crops benefit soil health, nutrient use efficiency, and weed management. Brassicas plants produce compounds that can control pathogens, especially if incorporated into the soil.

Of all the Brassica plants, spring-sown mustards have shown the most potential. Still, adequate water, fertility, and weed control are important to maximize biomass production for maximum biofumigation potential.

Soil Moisture

In the Brassicaceae family, broccoli, cauliflower and radish are shallow-rooted crops (6 -12 inches/15 -30 cm). Cabbage and Brussels sprouts are medium-depth rooted crops (12 – 18 inches/30 – 45 cm).

Root depth affects the watering frequency and cultivation practices. Deeper roots have access to gravitational water for longer.

The soil’s ability to drain water depends on particle size diversity, and water retention capacities depend on the soil’s cation exchange capacity (CEC).

The Role of Cation Exchange Capacity (CEC)

The higher the carbon content and microbial activity, the more water a field can retain after draining. In potting soil, balancing organic matter and inert materials like sand, perlite, pumice, and others, allows you to balance the drainage rate and the amount of water retained.

The freshly picked Brussels sprout is 74% water, but just about all the water you provide a plant is lost in transpiration and respiration. What the plant retains is used for turgidity and photosynthesis.

Brussels Sprout Water Needs

If you grow Brussels sprouts in a 10 x 4-foot or 3 x 1.2m bed, you can maximally grow 12 plants if you plant them with two-foot (60 cm) spacing in a zig-zag pattern. You must provide each plant with between 1 and 2 inches (25 – 50mm) of water a week. 

Each bed of that size needs 25 to 50 gallons (91 to 182 liters) of water per week if you’re flood-irrigating (which you can with plants with medium-depth roots).

Use Drip-Irrigation to Grow Brussels Sprouts

It’s essential to keep Brussels sprout leaves dry, so avoid sprinklers. Instead, by using drip irrigation, you can reduce the water consumption from a 40 square feet bed to a 12 square feet bed – a square foot per plant.

To flood a 40 square-foot bed an inch deep requires 120 x 48 inches of water (5,760 cubic inches or 24.91 gallons). In the metric system, a 3 x 1.2 m bed needs 91 liters (watering at a depth of 25mm).

Every square foot needs 144 cubic inches or 0.62 US gallons of water, or 30 cm2 needs 2.25 liters. If you drip-irrigate your 12 Brussels sprouts plants, you will use 27 or 7.44 gallons instead of the 25 gallons (91 liters), less than a third.

The above calculations are for an inch a week, but Brussels sprout may need as much as double that, depending on ambient temperatures and air circulation that affect transpiration rates.

The calculations are also based on 12 plants but may change depending on how many Brussels sprouts you can fit into a bed while maintaining a distance of about 24 inches (60 cm).

The Importance of Soil Oxygen When You Grow Brussels Sprouts

The next challenge is keeping the soil moist without driving all oxygen from it. Soil aeration is (again) a product of soil microorganism activity.

Anaerobic conditions are a perfect breeding ground for several Brussels sprout pathogens.

The Importance of Soil Oxygen in Young Seedlings

While you can plant Brussels sprouts directly into beds, the best results are achieved when you sow seeds into a tray of inert material. Don’t use compost or potting soil, opting for pumice or perlite. 

Planting Brussels Sprouts

Depending on your location, sow seeds outdoors about four months before the season’s first frost. Plant seeds in rows no closer than 30 inches (75 cm) apart at a quarter depth to half an inch (6 – 12 mm). Keep plants spaced at a minimum of 18 inches (45 cm).

Follow the directions on your seed packet, planting seeds outdoors about four months before the first fall frost date of the season.

Seed indoors in late May for Brussels sprouts seedlings to be ready for transplanting in late June or early July (mid to late summer). Keep seeds indoors moist and provide ample light.

Plant seedlings out at the spacing mentioned above. 

Transplanted Brussels sprout seedlings initially have a shallow root system, so water regularly and avoid cultivation. As the growing season continues, sprouts develop deeper roots.

Soil Temperature and Brussels Sprouts

Brussels sprouts prefer direct sunlight and fertile soil that drains well. Optimum Brussels sprout growth is in soil between 40 and 74°F/16 – 24°C. Soil temperatures below 50°F/10°C cause young roots to grow long, thin and pale.

Soil Fertility

Extra boron is often necessary for brassicas, and Brussels sprouts are no exception. Spray your Brussels sprouts with one teaspoon of Borax per gallon of water if your fertilizer lacks boron. 

Boron is a mineral that should be used cautiously as the line between it being beneficial and toxic is excellent, though the risk to Brussels sprouts is less than beans, for instance.

Due to the large, nutrient-heavy leaves cole crops produce, they need nitrogen. Apply 5-10-10 at 4.8 ounces (136 g) per 10 square feet (0.9 m²) before planting, then side-dress once during the growing season. 

Side-dress with 34-0-0 at 1.6 ounces (45 g) pound per 10 feet (3m) of row or 15.5-0-0 (calcium nitrate) at 3.2 ounces (90 g) per 10 feet (3m) of row.

You will notice that I’m not advising a balanced fertilizer (10-10-10) but upping the initial phosphorus and potassium and boosting the foliage growth once the apical meristem has been cut off, boosting lateral growth.

The Best Way to Harvest Sprouts

Pick fresh sprouts when they have a diameter of approximately one inch (25mm), are firm, and have developed a rich green color. Once they approach 2 inches in diameter, they lose their firmness.

You can either harvest Brussels sprouts as the sprouts reach the desired size or do a final harvest at the end of the season. 

You can harvest end-of-season Brussels sprouts by picking individual sprouts or cutting the entire stalk off with the attached sprouts. Brussels sprout is a high-yield, compact plant.

Harvesting the entire stalk is easy and extends the shelf-life of Brussels sprouts. Depending on the variety, wait until the first frost for a better flavor profile – sweet sprouts.

Brussels sprouts are a long-season crop, providing a fall harvest after 80-110 days of growth.

Brussels Sprouts Pests and Diseases

To protect your crop from pests, use row covers from early on. 

Common Pests

Cabbage Aphids – The aphids on your plants can be washed away with a strong water stream. In the morning, you should use water to clean off as needed. Look for alligator-like larvae of lady beetles and lacewings and gray-brown or bloated parasitized aphids.

Cabbage Root Maggot – The larvae of the white maggot burrow into plant roots and feed on the plant’s nutrients—damage results in early wilting and eventual plant death.

Cabbage Worms – Destroy by hand picking. When protecting young seedlings from early damage, row coverings may be advantageous. Set up at the time of planting and take down before the summer heat becomes unbearable.

Flea Beetles – You can delay the onset of harm to your plants using row coverings. Set up at the time of planting and take down before the summer heat becomes unbearable. Suppress weeds

Sunflowers can be a Beetle breeding site, so keep a reasonable distance.

Cutworms – Pull the weeds and protect your plants with cardboard collars.

Other Potential Brussels Sprout Pests:

• Cabbage loopers
• Nematodes
• Slugs

Preventing Brassica Diseases

To protect your Brussels sprouts from diseases:

• Ensure your soil pH is between 6.0 and 6.8
• Practice crop rotation
• Keep leaves dry (as far as possible)
• If leaves are wet, don’t work for the beds.
• Ensure optimal soil drainage.
• CompleteCompleteCompleteCompleteCompleteCompleteCompleteCompleteCompleteCompleteCompleteCompleteCompleteManage nematodes by boosting the beneficial microorganism populations by adding compost.Complete