How Temperature Affects Sprouts & Microgreens

Temperature can make a noticeable difference to how quickly sprouts and microgreens germinate and grow.

The same seeds grown using the same method may behave quite differently in a cool Australian kitchen in July compared with a warm room in January.

Cool conditions generally slow seed hydration, germination and growth. Warm conditions can accelerate them, but excessive heat combined with moisture and poor airflow can create problems of its own.

Understanding temperature helps you adjust soaking, rinsing, watering and harvest timing to the conditions rather than expecting every crop to follow exactly the same schedule throughout the year.

Quick Temperature Guide

Conditions	What You May Notice	What to Do
Cool	Slower soaking, germination and growth	Use the longer end of soak ranges and allow more growing time
Moderate	More predictable germination and growth	Follow normal crop instructions
Warm	Faster germination and water loss	Use the shorter end of soak ranges and monitor moisture closely
Very hot	Rapid drying, heat stress and greater moisture-management problems	Move crops to a cooler location and increase monitoring
Hot + wet + poor airflow	Unfavourable growing conditions and greater spoilage risk	Improve drainage and airflow and reduce excessive moisture

For many common sprouts and microgreens, a moderate indoor environment of approximately 18–24°C provides a useful general growing range.

This isn't a universal requirement. Different crops have different preferences, and successful growing is possible outside this range.

Why Does Temperature Affect Germination?

A dry seed is relatively inactive.

Once it absorbs water, biological processes associated with germination begin.

Temperature affects how quickly these processes occur.

Under cooler conditions, seeds generally:

• Absorb water more slowly

• Take longer to show visible germination

• Develop roots more slowly

• Take longer to reach harvest

Under warmer conditions, these processes generally occur more quickly — up to a point.

Excessive heat doesn't simply make plants grow better or faster. Very warm conditions can stress seedlings, increase water loss and make moisture management more difficult.

The goal isn't to make seeds as warm as possible.

The goal is to provide a suitable, reasonably stable growing environment.

Should You Soak Sprouting Seeds Longer in Winter?

Generally, yes — within the recommended soak range for that particular seed.

This is one of the simplest seasonal adjustments you can make.

OzSprout often gives soaking instructions as a range because conditions vary.

For example, if a seed has a recommended soak time of:

8–12 hours

you might use approximately:

• 8 hours in warm summer conditions

• 10 hours in moderate conditions

• 12 hours in cooler winter conditions

Likewise, for a seed with a recommended soak of:

6–8 hours

you might favour:

• Around 6 hours during warmer conditions

• Closer to 8 hours during cooler conditions

The principle is:

Warmer conditions → shorter end of the recommended soak range

Cooler conditions → longer end of the recommended soak range

This doesn't mean every seed should be soaked overnight during winter.

Some varieties have deliberately short soaking periods and should still be treated accordingly.

For example, buckwheat requires a very short soak compared with beans and legumes. Broccoli also has a shorter recommended soak than many larger seeds.

Always start with the crop-specific range in our Sprouting Seed Guide: Soak Times, Quantities & Harvest Times and adjust within that range according to conditions.

Why Use a Shorter Soak During Summer?

Warm water and warm room conditions accelerate biological activity.

Leaving seeds submerged unnecessarily long during hot weather isn't beneficial simply because a longer soak works well during winter.

During warm conditions, use the shorter end of the recommended soaking range and drain the seeds once they have had sufficient time to hydrate.

This becomes particularly important during Australian summer conditions when indoor temperatures can remain high overnight.

If you're soaking seeds in a very warm kitchen, don't automatically leave them submerged for the maximum recommended time.

What Happens When Sprouts Are Too Cold?

Cool conditions usually don't cause an immediate crop failure.

More commonly, everything simply happens more slowly.

You may notice:

• Seeds taking longer to germinate

• Roots appearing later

• Slower stem development

• A longer harvest period

• More uneven-looking early germination

Don't assume slow germination means the seed is faulty.

If the seeds still look and smell normal, continue following the appropriate rinse-and-drain routine and allow additional time.

Our Sprouting Seeds Not Germinating? Troubleshooting Guide covers the other factors to check when germination is slower than expected.

What Happens When Sprouts Are Too Hot?

Very warm conditions can make jar sprouting more difficult.

Seeds may germinate quickly, but heat can also increase:

• Moisture loss

• The need for monitoring

• Temperature inside a dense mass of sprouts

• The consequences of poor drainage

• The risk of deterioration under warm, wet conditions

During hot weather:

• Keep sprouting jars away from direct sunlight.

• Maintain good airflow.

• Drain thoroughly after every rinse.

• Check the sprouts more frequently.

• Adjust rinsing if conditions require it.

• Harvest promptly once sprouts reach the desired stage.

A hot windowsill is not a good location for a sprouting jar.

Does Rinse Frequency Change With Temperature?

It can.

Most common jar sprouts are rinsed and thoroughly drained approximately 2–3 times daily, although individual crop instructions vary.

During warm or dry conditions, sprouts may require closer monitoring and potentially an additional rinse.

During cooler conditions, don't compensate for slow growth by leaving sprouts continuously wet.

The principle remains the same regardless of season:

Rinse thoroughly → drain thoroughly → maintain airflow.

Sprouts need moisture, but they shouldn't remain sitting in water.

Should You Use Warm or Cold Water for Sprouts?

For routine home sprouting, use clean, drinking-quality water at a normal cool or room temperature.

Avoid extremes.

Very hot water can damage seeds and developing sprouts, while there is generally no need to use icy water.

During hot weather, normal cool tap water can also help avoid adding additional heat to an already warm sprouting environment.

The water should support normal rinsing and hydration rather than being used as a way to deliberately heat or chill the crop.

Why a Sunny Windowsill Can Be Too Hot

A room may feel comfortable while a sunny windowsill becomes considerably hotter.

Direct sunlight through glass can heat:

• Sprouting jars

• Water remaining in the jar

• Microgreen trays

• Growing medium

• Seedlings

This can happen surprisingly quickly during Australian summer conditions.

Sprouts don't need to sit in direct sunlight to grow successfully.

Leafy sprouts can be exposed to bright indirect light toward the end of their growing period if you want the seed leaves to green.

Microgreens require good light after blackout, but that doesn't mean placing them in intense direct summer sun.

How Temperature Affects Microgreen Germination

Temperature affects microgreens from the moment the seed is sown.

Under cooler conditions:

• Germination may take longer.

• Emergence may be slower.

• Blackout periods may need to be judged by development rather than the calendar.

• Overall harvest may take longer.

Under warmer conditions:

• Germination may occur faster.

• Growing medium may dry more quickly.

• Seedlings can require water sooner.

• Blackout may progress faster.

• Crops may reach harvest earlier.

This is why growing instructions should be treated as a starting framework rather than an exact stopwatch.

Temperature During Microgreen Blackout

Microgreen blackout creates a particularly important temperature consideration.

Seeds and young seedlings are close together, surrounded by moisture and often covered, stacked or weighted.

That environment can retain warmth.

During warm weather, regularly check trays rather than simply leaving them covered for the maximum number of days stated in a guide.

If germination is progressing faster than expected, the crop may be ready to move to the next stage earlier.

For a detailed explanation, see our Microgreen Blackout Explained: Why, How & How Long? guide.

Can Stacked Microgreen Trays Get Warmer?

Yes.

A stack of germinating trays can retain heat differently from an uncovered tray sitting in open air.

This matters particularly when:

• Room temperature is already high

• Several trays are stacked together

• Seeds are densely sown

• Growing medium is very wet

• Air circulation around the stack is poor

During warm conditions, check stacked trays regularly.

Don't assume that because the surrounding room feels acceptable, the conditions inside every covered tray are identical.

How Temperature Changes Microgreen Watering

Temperature and watering are closely connected.

During Warm Weather

Water evaporates more quickly from:

• Growing medium

• Tray surfaces

• Leaves

Microgreens may therefore need more frequent monitoring.

Don't respond by automatically saturating the growing medium.

Check the moisture level and water according to what the crop actually needs.

During Cool Weather

Growing medium generally remains wet for longer.

If you continue applying the same amount of water as during hot weather, the root zone may remain excessively wet.

Allow the crop and growing medium to guide watering frequency.

Our How to Water Microgreens: Misting vs Bottom Watering guide explains the different watering stages in more detail.

Australian Summer Sprouting Tips

Australian summer conditions can vary enormously, but prolonged warm weather requires more attention than a mild indoor environment.

During hot weather:

• Use the shorter end of the recommended seed-soaking range.

• Soak seeds away from hot direct sunlight.

• Keep sprouting jars in a well-ventilated indoor location.

• Drain particularly thoroughly.

• Monitor sprouts more frequently.

• Adjust rinsing frequency when required.

• Keep jars away from hot windows.

• Harvest promptly when sprouts are ready.

• Refrigerate harvested sprouts promptly.

If your kitchen becomes extremely hot during the day, look for a cooler suitable location elsewhere in the home.

Australian Winter Sprouting Tips

During winter, the most common difference is slower growth.

You may need to:

• Use the longer end of the recommended soaking range.

• Allow more time for germination.

• Allow additional time before harvest.

• Keep jars away from very cold windows overnight.

• Choose a reasonably stable indoor location.

• Be patient with varieties that are naturally slower to germinate.

Don't attempt to compensate for cold conditions by putting jars directly against heaters or other strong heat sources.

A moderate, stable temperature is preferable to extreme heating.

Australian Summer Microgreen Tips

During warmer months:

• Check germinating trays frequently.

• Don't leave trays covered simply because the maximum blackout time hasn't passed.

• Monitor growing-medium moisture closely.

• Increase airflow where appropriate.

• Avoid intense direct afternoon sun.

• Bottom water according to actual crop needs.

• Harvest promptly once the crop reaches the desired stage.

Fast-growing varieties may move through their normal stages more quickly during warm conditions.

Australian Winter Microgreen Tips

During cooler months:

• Expect germination to take longer.

• Don't assume a crop has failed because emergence is slower.

• Avoid overwatering growing medium that is drying slowly.

• Keep trays in a stable indoor environment where possible.

• Provide good light once seedlings leave blackout.

• Expect some crops to take longer to reach harvest.

Again, judge the crop by its development, not only by the number of days on the calendar.

Do You Need a Heat Mat?

Not necessarily.

For many Australian homes, indoor temperatures are suitable for growing common sprouts and microgreens for much of the year.

A heat mat can be useful in genuinely cold environments or for crops that prefer warmer germination conditions, but it isn't automatically required.

If using one, temperature control is important.

More heat isn't necessarily better.

A heat mat can also cause growing medium to dry more quickly, so moisture needs closer monitoring.

For many growers, choosing a suitable indoor location is simpler than adding supplemental heat.

What Should You Do During a Heatwave?

During periods of unusually hot weather, focus on keeping the crop out of excessive heat rather than trying to follow the normal calendar rigidly.

For sprouts:

• Move jars to the coolest suitable indoor location.

• Keep them out of direct sunlight.

• Maintain airflow.

• Rinse as required.

• Drain extremely well.

• Check crops frequently.

For microgreens:

• Move trays away from intense direct sunlight.

• Check growing-medium moisture more frequently.

• Maintain airflow.

• Monitor covered and stacked trays closely.

• Harvest crops that are ready rather than leaving them unnecessarily long.

If indoor temperatures remain extremely high, delaying a new crop until conditions moderate can sometimes be the simplest option.

Temperature Troubleshooting Guide

What You're Seeing	Possible Temperature Issue	What to Do
Seeds germinating very slowly	Too cool	Move to a moderate indoor location and allow more time
Sprouts ready much earlier than expected	Warm conditions	Judge by development and harvest when ready
Seeds slow after winter soaking	Cool water/room	Use the longer end of the recommended soak range
Seeds soaking during hot weather	Warm conditions	Use the shorter end of the recommended soak range
Growing medium dries rapidly	Warm or dry conditions	Check moisture more frequently
Growing medium stays wet for days	Cool conditions	Reduce unnecessary watering and improve airflow
Microgreens emerge early during blackout	Warm germination conditions	Check development and move to the next stage when ready
Covered trays feel unusually warm	Heat retained during germination	Improve conditions and monitor more frequently
Sprouting jar becomes hot in sunlight	Direct solar heating	Move it to bright indirect light or a suitable indoor location
Winter harvest takes longer	Slower growth	Allow additional time

Temperature Is One Part of the Growing Environment

When a crop isn't behaving as expected, temperature is worth checking — but it isn't the only factor.

Successful sprouts depend on the interaction between:

• Seed quality

• Soaking

• Moisture

• Drainage

• Airflow

• Temperature

• Time

Microgreens also depend on:

• Growing medium

• Seeding density

• Blackout

• Light

• Watering

• Airflow

Changing one factor can affect several others.

For example, warmer conditions increase water loss, while cooler conditions allow growing medium to remain wet for longer.

Good growing is therefore less about following a rigid schedule and more about understanding what the crop needs at each stage.

Frequently Asked Questions

What is the best temperature for growing sprouts?

Many common sprouts perform well in moderate indoor conditions around 18–24°C, although individual varieties differ.

Avoid excessive heat and very cold conditions where possible.

Should I soak seeds longer in winter?

Generally, use the longer end of the seed's recommended soaking range during cooler conditions.

For example, an 8–12 hour soak might be closer to 12 hours during winter and closer to 8 hours during warm summer conditions.

Don't exceed crop-specific instructions simply because it is winter.

Should I soak seeds for less time in summer?

Generally, yes.

During warm conditions, favour the shorter end of the recommended soaking range.

Warm conditions encourage faster hydration and biological activity, so there is usually no benefit in leaving seeds submerged for the maximum time unnecessarily.

Do sprouts grow faster in summer?

They often germinate and develop faster under warmer suitable conditions.

However, excessive heat can create problems rather than improving growth.

Why are my sprouts taking so long in winter?

Lower temperatures slow seed hydration, germination and growth.

If the seeds look and smell normal and you're following the correct method, they may simply need additional time.

Should I rinse sprouts more often in summer?

Possibly.

Warm and dry conditions can increase moisture loss. Monitor the sprouts and adjust rinsing where necessary while continuing to drain thoroughly after every rinse.

Do microgreens grow faster when it's warm?

Within a suitable temperature range, warmer conditions can speed germination and growth.

Excessive heat can stress seedlings and make watering and moisture management more difficult.

Should I use a heat mat for microgreens in winter?

Only if conditions are genuinely too cool for reliable germination or the crop specifically benefits from additional warmth.

Many microgreens can be grown successfully indoors without a heat mat.

Can I put sprouts or microgreens in direct sunlight to warm them up?

This isn't a good way to control temperature.

Direct sunlight can rapidly heat jars and trays beyond the surrounding room temperature, particularly through a window.

Choose a more stable indoor location instead.

Adjust the Method to the Season

The biggest lesson is that growing instructions shouldn't be treated as completely independent of the environment.

In cooler winter conditions:

Soak toward the longer end of the recommended range → expect slower germination → allow more growing time.

In warmer summer conditions:

Soak toward the shorter end of the recommended range → monitor moisture more closely → expect faster development.

Always stay within the instructions appropriate to the particular seed.

For crop-specific soak times, quantities and harvest periods, see our Sprouting Seed Guide: Soak Times, Quantities & Harvest Times.

If your sprouts aren't germinating as expected, use our Sprouting Seeds Not Germinating? Troubleshooting Guide.

For microgreens, see How to Grow Microgreens at Home in Australia and How to Water Microgreens: Misting vs Bottom Watering.

Browse the OzSprout Sprouting Seeds and Microgreen Seeds ranges for individual crop growing instructions.