Brussels sprouts are a healthy and delicious vegetable that can be grown in home gardens or commercially. They are a member of the cabbage family and look like miniature cabbages. Brussels sprouts grow on a stalk and mature from the bottom up, with the lowest sprouts ready to harvest first. Knowing the best temperatures for growing brussels sprouts can help ensure a productive crop.
Optimal Day and Night Temperatures for Brussels Sprouts
Brussels sprouts prefer cool temperatures, ideally with daytime highs of 65-75°F (18-24°C) and nighttime lows around 55-65°F (13-18°C). They can tolerate temperatures down to 45°F (7°C) at night. Temperatures above 80°F (27°C) can cause them to bolt or flower prematurely, resulting in loose sprouts. Here are the optimal day and night temperature ranges:
Daytime High Temperatures
| Temperature Range (°F) | Temperature Range (°C) |
| 65-75 | 18-24 |
Nighttime Low Temperatures
| Temperature Range (°F) | Temperature Range (°C) |
| 55-65 | 13-18 |
Maintaining temperatures in these optimal ranges will support the growth of firm, compact brussels sprout heads.
Ideal Growing Seasons and Months
Because they prefer cooler temperatures, brussels sprouts grow best during the fall in most climates. In many areas, brussels sprouts are grown as a fall crop for harvest in late autumn or early winter.
Here are some guidelines on the best times to plant and harvest brussels sprouts:
Northern Climates
In northern areas with cold winters, the ideal growing season is late summer through fall. Plant seeds in June or July for harvest between October and December. The cooler fall temperatures help the plants mature properly.
Southern Climates
In southern regions with mild winters, grow brussels sprouts as a winter crop. Plant seeds in late summer or early fall and harvest during winter. Avoid the hot summer months.
Coastal Climates
Along coastal zones with temperate weather, brussels sprouts can be grown as a winter or spring crop. Plant seeds in late summer for winter harvests or in winter for spring harvests. Avoid summer heat.
Ideal Harvesting Months
| Climate | Ideal Harvesting Months |
| Northern | October to December |
| Southern | December to February |
| Coastal | December to February or March to May |
Targeting the cooler seasons and months will provide the best temperatures for maturing brussels sprout plants.
Optimal Soil Temperature for Planting
In addition to air temperatures, soil temperature is also important when planting brussels sprout seeds or transplanting seedlings.
Brussels sprouts grow best when planted into soil that is at least 46-86°F (8-30°C). The ideal soil temperature for planting is around 59-68°F (15-20°C). Warmer soils will help seeds germinate faster and support better stand establishment.
Before planting, use a soil thermometer to check that the soil has warmed to within the optimal range. Planting when the soil is too cool can lead to erratic or poor germination.
Using Row Covers for Temperature Control
Row covers made from fabric or plastic sheeting can be placed over brussels sprout plants to help regulate temperatures for growth. Benefits include:
– Retaining heat to protect sprouts in cool weather
– Providing 1-8°F of frost protection
– Creating a warmer microclimate to extend the growing period
– Preventing overheating during warm spells
Use floating row covers directly over plants, or support covers with hoops to keep the material elevated. Ensure airflow and ventilation. Remove covers once sprouts are established or temperatures rise.
Avoiding Hot Temperatures
While they thrive in cool conditions, brussels sprouts do not tolerate hot weather well. Temperatures above 80°F (27°C) can trigger the following problems:
Premature Bolting
In response to heat stress, brussels sprout plants may bolt or prematurely flower. This stops the production of sprouts. Bolting is most likely to occur if temperatures exceed 85°F (29°C).
Loose Sprouts
Heat causes brussels sprout heads to remain loose and fail to form tight buds. Hot days and cool nights can aggravate this issue.
Poor Growth
Extended periods of heat may stunt the plant’s growth or cause leaves to yellow. Development of sprouts is inhibited.
Bitter Flavor
Heat exposure can cause sprouts to develop a bitter taste. Temperatures above 75°F (24°C) are linked to bitterness.
To avoid heat damage, monitor weather forecasts during the growing season. Provide shade with row covers if hot spells occur. Grow heat-tolerant varieties like Oliver, Prince Marvel, or Churchill.
Providing Cool Conditions
If dealing with high summer temperatures, there are some methods to help keep brussels sprouts cool:
– Plant in partial shade or dappled sunlight to reduce heat from direct sun.
– Use shade cloths or screens to block 30-50% of sunlight over the plants.
– Mist plants over the tops of leaves to provide evaporative cooling.
– Use reflective mulch like aluminum foil to bounce sunlight and heat off the ground.
– Amend soil with compost to retain moisture and keep roots cooler.
– Grow brussels sprouts close together for mutual shading between plants.
How Temperatures Affect Brussels Sprouts
The growth of brussels sprouts throughout their life cycle is directly influenced by temperatures. Here is a more detailed overview:
Germination
– Minimum soil temperature for germination: 46°F (8°C)
– Optimal soil temperature for best germination: 59-68°F (15-20°C)
– Seeds fail to germinate well in cool soil below 50°F (10°C)
Seedling Growth
– Continued cool temperatures below 60°F (16°C) will slow seedling development
– Temperatures between 60-70°F (16-21°C) support robust seedling growth
– Growth stunted above 80°F (27°C)
Sprout Initiation
– Sprouts begin developing after 4-6 weeks of growth
– The process requires cool temperatures between 60-70°F (16-21°C)
– Warmer temperatures inhibit sprout formation
Sprout Fill Out
– Once initiated, sprouts fill out over 2-3 weeks
– Cool weather between 60-75°F (16-24°C) optimizes sprout enlargement
– Sprouts remain loose and open under warm temperatures above 80°F (27°C)
Maturity
– Sprouts reach full size after 8-12 weeks from planting
– Continued cool fall temperatures ensure tight, compact sprout heads
– Hot weather causes premature flowering and loose sprouts
Using Growing Season Extension Methods
In some regions, the natural outdoor growing season does not provide cool enough conditions for brussels sprouts. This is often the case in hot summer climates.
Several season extension techniques can be used to manipulate temperatures for growing brussels sprouts:
Greenhouses
Unheated greenhouses provide frost protection and warmer conditions to extend the fall or spring growing period. Ventilation and shade cloth will be needed in warm climates.
High Tunnels
High tunnels are temporary unheated greenhouse structures that help lengthen the growing season. They keep plants warmer in late fall/winter and prevent overheating in spring/summer.
Cold Frames
A cold frame is an unheated enclosure that sits directly on the ground. It traps solar heat while protecting plants from frost and wind. Use for growing brussels sprouts in early spring or late fall.
Row Covers
As mentioned previously, floating row covers retain heat and can raise temperatures around plants by a few degrees. They provide light frost protection.
These methods allow growing brussels sprouts outside of their normal cool season window in challenging climates. With protection from heat and cold extremes, sprouts can thrive year-round.
Ideal Temperatures for Brussels Sprouts in Summary
– Brussels sprouts grow best with cool daytime highs around 65-75°F (18-24°C) and nighttime lows of 55-65°F (13-18°C).
– Optimal sprout development occurs between 60-70°F (16-21°C).
– Plant seeds when the soil reaches 55-65°F (13-18°C).
– Hot temperatures above 80°F (27°C) reduce sprout quality and yield.
– The fall season provides perfect growing conditions in many regions.
– Season extension methods allow growing sprouts year-round in unfavorable climates.
Following the ideal temperature conditions for brussels sprouts leads to a healthy, productive crop with a bountiful fall harvest. With proper care to regulate their growing environment, beautiful brussels sprouts can be grown in almost any climate.
Conclusion
Brussels sprouts thrive under cool conditions but are highly sensitive to extreme heat. By adhering to their preferred temperature ranges throughout the growing season, luscious sprouts can be cultivated in home gardens or on a commercial scale. Tracking seasonal weather patterns and using protective growing structures enables successful brussels sprout harvests even in challenging climates not suited to fall production. When temperatures are maintained within an optimal zone, from germination through maturity, brussels sprouts will prosper and yield abundantly.