How to Water Microgreens: We Find This Is The Best Way

Let me prefix this article on how to water microgreens with all my experience watering microgreens grown on or in soil. Although I have grown microgreens on grow mats, I must work out several things, including watering.

Let’s get to watering microgreens grown on soil.

The short answer is you need to water microgreens from the bottom. Never mist the tops. You want to water when the soil in the tray is becoming dry. The tray will feel light. 

We have found that most people overwater microgreens, which leads to the root of most problems.  However, the watering frequency depends on the growth phase and many physical-environmental factors.

We have also made a video showing our processes for how to water microgreens. By all means, watch the video included in the article. The best way to learn is to watch. 

How to Water Microgreens – When & How Much

When people think about how to water microgreens, they imagine a tray of mature microgreens growing on a shelf.

But, we need to break watering down into several phases of microgreen growth to tell the whole story.

If you’re new to my methods of growing microgreens, you should read the information in all phases.

You can click the links in the green-colored tables to move around the article.

Watering by Growth Phase

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Before we get to the phases, let’s not forget the factors affecting watering microgreens. We will list them here and discuss them in detail below.

Factors that Affect Watering Microgreens

How to Water Microgreens the Video

The video below shows the processes of watering microgreens in several phases and with different size trays.

Please watch.

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Microgreens Podcast

We have also created a podcast where we discuss watering microgreens.

Give it a listen! If you want to subscribe to the podcast, click here and choose your favorite Podcast provider.

The Microgreens Podcast Episode 022

What Type of Water?

We have experimented with all kinds of water. These include tap water, bottled water, RO water, low pH, high pH, neutral pH, cold water, warm water, chlorinated water, non-chlorinated water, and spring water.

What did we find?

There is no noticeable difference in growth, flavor, or anything regarding the microgreens. Some water parameters, such as pH might affect the absorption of liquid fertilizers. Still, since we don’t use those, we use tap water poured into gallon jugs.

I have better things to do than adjust the pH or conductivity of my microgreen water for no noticeable difference.

Watering Microgreens in Bulk

One method I didn’t address in the video is bulk watering or watering serval planting trays inside one larger watering tray simultaneously.

We’ll further discuss how to water microgreens in bulk in the article. 

Watering Microgreens In Each Growth Phase

When and how much you water depends on the growth phase of the microgreens.

Watering Microgreens Before & After Sowing Seed

It seems odd to water microgreens even before you have sowed the seed, but that is what you are doing.

Microgreen seeds do not germinate well in dry soil. So you need to add water, which in my book is watering microgreens.

So many microgreen growers and bloggers recommend wetting the soil mass before spreading the seed.

You are not creating cement. Therefore, there is no need to mix water into your soil to the point where the whole soil mass is damp, moist, or wet.

More on why this isn’t a good idea is below.

The Correct Way to Wet Soil Before & After Seeding Microgreens

1. Place the soil in the tray, level, and smooth the surface.
2. Use a spray bottle or pump sprayer and wet only the upper 1/3 of the soil profile. 
3. Spread your seeds evenly on the wetted soil surface.
4. Mist the seeds again to wet the surface and help settle them into the soil.
5. Cover with coroplast, I call them tray separators, or you can use another tray for blackout or a dome.

Why Not Wet the Whole Soil Profile?

Think of the tray of soil as the atmosphere. 

When the air is full of water and very humid, the weather is unsettled, and it’s only a matter of time before a storm brews.

Same in the soil profile. All that extra water stored in the soil is useless as the seed and seedling only need moist soil around and near it.

Water in the lower part of the tray will evaporate and rise to the surface, condense on the cover, and fall back to the already moist upper surface of the soil.

Drenching the seed and encouraging mold and bacterial colonies to grow. 

When only the upper surface of the soil is wet, water that evaporates and condenses will drip back to the now drier soil surface. This keeps it at more constant wetness.

Less is best.

This statement will be valid throughout this article.  

Watering Microgreens During Germination

The only time you should water microgreens while they are germinating or during the blackout period is when the edges of the soil turn a much lighter color than the middle of the tray.

Drying of the soil during the blackout period only happens for seeds that take a long time to germinate, i.e., celery, or if there is a lot of air movement around the tray. 

Sometimes, the cover or lid doesn’t completely enclose the soil surface with the Home Microgreens Tray, and drying can occur. But usually, no seeds are on the upper edge, so watering is unnecessary. 

Only mist the seeds if the surface soil is dry. If this happens, remember it, and the next time you plant microgreen seeds, water the soil a bit deeper during sowing.

Only mist, don’t water the tray.

Also, consider what happens when the lid is lifted. Will it upset more seeds than those that are dry? Sacrifice a few for the greater good if that is the case.  

How to Water Microgreens After Blackout – First Light

When the microgreens are ready to come out of the blackout and go under the lights is the first time we water microgreens with any volume of water. 

We will assume you have the planting tray in a watering tray. However, if you plan to place several microgreens trays into one larger watering tray, click here for recommendations.

To bottom water, lift an end or corner of the planting tray and pour the recommended amount of water into the watering tray. 

Bottom Water Only

Then gently lower the planting tray back into the watering tray. The pressure of the planting tray will lift the far end so water will flow evenly across the tray.

The weight of the planting tray will force the water up between the two trays causing a pressure gradient.

The gradient will force water up into the holes in the bottom of the planting tray wetting the soil media.

A good potting soil composted of coconut coir or peat moss will wick water upwards into the soil profile. 

How Much Water to Use for Each Microgreen Tray?

Here are our recommendations for how much water to add to each microgreen tray when it is about dry.

• Home Microgreens Tray (7-1/2 by 5 inches) uses 1/2 to 9/16 cups of water.
• 1010 tray (9-1/2 by 9-1/2-inches), use 1 cup of water.
• 1020 Tray (9/1/2 by 19-3/4-inches) use 2 cups of water.

If the tray isn’t dry, but you are going away for a few days, adjust accordingly.

We like these measurements because if you add more than the recommended amount, a tight-fitting watering tray will likely force the water out and onto the floor.

Making it almost impossible to overwater in one watering.

However, you can overwater by not waiting until the tray is dry, i.e., daily watering.

Watering Young Microgreens

The initial watering might be all the water your microgreens need for the first week. 

After that, it will depend on many watering factors we discuss later in the article.

Use the recommendation in the DO THIS box. 

Lift the tray and evaluate the weight. If it’s light, water. If not, check back tomorrow or the next day.

Under many circumstances, I’ve only had to water microgreens when they went under the lights and one more time before they were harvested. 

The physical and environmental factors will come into play with watering frequency.

Most microgreen varieties will even come back after wilting. 

Less is best in most cases.

Watering Long Growing Microgreens

I call microgreens that take 14 or more days of growth before harvesting long-growing microgreens. 

We can make some generalizations about watering long-growing microgreens as far as watering.

They need more frequent watering as they get older.

The two main reasons are that greens are using more water to sustain growth; and, the root mass has increased, and there is less room for water.

Where does the soil go? 

I ask myself this every week when I grow peas. The whole tray is rooted, but the soil level doesn’t seem to rise up. Where does it go?

I’m asking because I haven’t figured it out yet.

Anyway, be careful as these generalizations and assumptions can, well, you know the saying.

I often overwater basil and mustard as the trays get older because I think they use more water. I don’t follow my own DO THIS advice.

Some plants don’t have robust root systems (basil), and others don’t seem to use as much water (mustard).

But as a tray of microgreens gets older, it’s best to check the weight of the tray more often as, most likely, the plants will use more water. 

Watering Microgreens Pre-harvest

We have found it best to water a tray of microgreens a day before harvesting the greens.

If you are cutting only what you need for a meal and letting the rest of the tray grow, don’t worry about this watering event unless you are tipping the tray to harvest. Water may drip out if the plants haven’t had time to use the excess.

However, if you harvest the whole tray or most of the tray, the microgreens are in prime condition when watered the day before.

They are plumper, firmer, and juicier.

Those are technical terms for yummier. 

Any time after that, the tray will be wet and more challenging to harvest. Either by making your harvesting area wet or water dripping out of the watering tray when you tip it to harvest.

Having the soil too wet makes it hard to dump the soil into the compost container.

Factors that Affect When to Water

Now that we have talked about watering microgreens during their different stages of growth. Let’s discuss the factors that can affect the time between watering.

Notice that I didn’t say how much to water. This is because I always water the exact amount based on our recommendations. 

It’s more about timing that amount. 

Room Temperature

An obvious environmental factor. The warmer a room is, the faster the microgreens will grow, causing more evaporation and transpiration.

Our ideal temperature is between 68- and 75 degrees. We don’t follow our recommendations here because we can’t control or afford to control the environment. Our rooms range from 50- to 90 degrees depending on the season.

The warmer a room is, the more often you must check if your trays need water.

Soil Temperature

This may matter if you’re using a heat mat or your trays are above lights that are putting out heat.

In both cases, I place an empty tray upside down over the heat source, then place the tray of microgreens on that. It reduces the direct heat.

Obviously, the higher the soil temperature, the more frequently you need to water.

Humidity

Humidity is good, to a point, then it’s a problem. If you can control the air humidity around your growing area, keep it around 60%. 

If not, the drier the air, the more frequently you must water your microgreens. 

Interestingly, high humidity doesn’t reduce watering frequency compared to moderate moisture. Most likely as the plants transpire more. The additional moisture does increase the chances of disease or fungal attacks.

Air Movement

Air movement around your trays can have the most significant impact on your watering frequency. 

High-volume fans or microgreen trays near open windows cause evaporation to increase significantly. 

When we use fans (when it is very humid), they are small USB-driven computer fans. You don’t notice them blowing air unless you place your hand above the tray.

But even that low volume of air movement can dry out trays quickly. In addition, trays closer to the fan will need more attention than those two or three tray lengths away from the source. 

If you need to use a fan, check the trays’ weight more frequently.

Soil Composition

We recommend soil composted of either coconut coir or peat moss, or a combination. Both hold water well, but peat is hard to wet. So if it becomes dry, it is much harder to re-wet.

Coconut coir also wicks water faster. Therefore, it is the best choice.

However, using pure coir or peat is not ideal, either. As both lack nutrients and microgreen growth will suffer.

We have a lot of articles on the best soils to use.

Adding perlite to the soil mix is a good idea. It improves water and airflow in the soil but has tens of thousands of tiny pores that retain water and oxygen for the plants.

We do not recommend heavy soils – those with compost. Or very light soils – seed-starting soils.

The first is too heavy, holds too much water, and has few air spaces; the latter are nutrient-poor and dry out too quickly.

Tray Soil Volume

The deeper microgreen tray can hold more soil; if that soil retains water well, it can reduce the number of times you need to water the microgreens.

However, it’s not all peaches and cream. 

Using too much soil can be wasteful and more expensive. Most commonly grown microgreens (exceptions are sunflowers & peas) do not root deeply. Besides acting as a water reservoir, the extra soil is useless.

We recommend using either the Home Microgreens trays or shallow microgreen trays. We carry the shallow 1010 trays, and shallow 1020 trays can be purchased at Bootstrap Farmer. 

All of these trays are about 1-1/4 inches deep.

We also wrote an article on these trays. 

Deeper trays are not necessary unless you grow microgreens in an arid environment. However, growing pea microgreens in deeper trays can increase the number of cuttings you get from a tray. That can be worthwhile.

Microgreen Variety

Some microgreen varieties use more or less water than others. 

Other than saying microgreens like basil and mustard use much less water than peas or sunflowers, we will not get into listing light or heavy water users.

But be aware that microgreens use different amounts of water from variety to variety.

Some microgreen varieties are susceptible to damping-off disease. Therefore, beets, Swiss chard, and amaranth, to name a few, should not be overwatered. They should be monitored more closely and kept near the dry side for better growth.

Microgreen Age

We mentioned this in the phase review. But in case you didn’t read that section, we have included it here. 

The older a microgreen is, the more water it will generally use. This is because even though they might not grow as fast, they have larger leaves to support, which also transpire more water.

Another factor is that the root mass is more extensive, and the tray might not take as much water. Root mass will depend on the variety.

Tray Size

We aren’t talking about how much soil the tray can hold. We mentioned that earlier. What we are talking about here is the overall size. A smaller tray holds less soil and more outside surface area than a larger one.

The smaller tray will dry out quicker. 

If you grow in different-size trays, it will be hard to water all on a regular schedule as they will have other requirements.

Tray Layout

It’s best to keep those trays touching when growing more than one tray. 

Conditions in the trays will stay more consistent. 

If one variety grows over the edge, you must space them. Also, if the humidity is high, space them out to increase airflow.

But otherwise, keeping the trays touching is beneficial to the microgreens.

Light Intensity

The effects of light intensity are interesting. 

I have been watching microgreens under many different lights and growth dependent on light height above the microgreens.

Light intensity (I’ll also throw in seeding density) has everything to do with growth habits. More on that in another article, but it also affects the watering schedule. 

Besides the apparent increase in heat between stronger and weaker lights, the more intense the light (more wattage), the less water the plant uses.

We think this is because the extreme light intensity decreases the leaf size, and the plant doesn’t lose as much water to the air.

The shorter growth might also cause denser foliage and decrease the air movement across the soil surface. 

We have more work to do with light intensity and see if grow lights produce better microgreens.

Not saying that you need to use grow lights, not at all. Shop lights grow great-looking microgreens. But grow lights change the physiology of the plant.

The question is does the increased energy produce more nutrients? Need to find an inexpensive way to test that. Need to find an inexpensive way to test that.

We also need to consider the expenses. If there is an increase in nutrients, is that gain worth the initial extra cost of grow lights and the energy cost to run them?

The point is microgreens under a bank of grow lights will have different water requirements than those grown under shop lights.

Your Availability

When we say DO THIS, we know it isn’t black & white. There will be times when it isn’t evident whether the tray is dry or not. 

Here’s how we handle that. As long as the tray isn’t by an open window or some other air movement or heat source, we let it go.

Less is best.

However, we water the tray if we are hiking the next day or will not be around to check on the microgreens. So we might water it with half as much water.

Less is best.

If we know we will ignore them longer, we water them with the total recommended volume for that size tray.

If you are available to water, remember that less is best and let them go another day. If you have less time to pay attention to them, water them more each time.

One More Thing on How to Water Microgreens

It is best to grow your microgreens where you can see them many times during the day.

Out of sight, out of mind.

We have one rack (a rack system we are testing) that doesn’t see a lot of traffic throughout the day.

The microgreens and lettuce on that rack system have been found wilted or worst a few times. 

We know it’s not always possible to grow microgreens in plain sight. But if you can, you should.

The one thing I like more than eating microgreens is watching them grow, so I don’t have any qualms about growing them in plain sight.

Bulk Watering Microgreens

We often place more than one planting tray in a larger watering tray to save time.

It is easier and quicker to water in this fashion.

However, you still need to DO THIS and check each tray to see if it needs water. Then, try to group microgreens that have the exact water requirements together.

If you can’t, remove the trays that don’t need watering before adding water to the larger tray. 

Bulk watering microgreens is the way to go, but keep up your diligence on which ones need water and those that don’t. 

Summary of How to Water Microgreens

Wet only the upper 1/3 of the soil profile when you sow seeds.

Except for sowing, always bottom water your microgreen trays. 

Always.

The first time you water is when the microgreens go under the lights.

DO THIS

Remembering the weight of the tray as they go under the lights is the best thing you can do. There will be a noticeable difference in weight between a tray that needs water and one that does not. 

There is no schedule.

There are many physical and environmental variables that it’s almost impossible to say water on days 3, 5, 7, and 9.

Many websites I looked at said water every other day.

You can’t count on that. Often microgreens don’t need that much water.

Less is best.

Maybe you can schedule to check the trays’ weight every other day. But not water them.

Our recommended water volumes. 

How Much Water to Use for Each Microgreen Tray?

Here are our recommendations for how much water to add to each microgreen tray when it is about dry.

• Home Microgreens Tray (7-1/2 by 5 inches) uses 1/2 to 9/16 cups of water.
• 1010 tray (9-1/2 by 9-1/2-inches), use 1 cup of water.
• 1020 Tray (9/1/2 by 19-3/4-inches) use 2 cups of water.

Water requirements change as the microgreens change. Therefore, you need to be flexible to these changes.

Keeping microgreens where they can be observed is much better than in a less frequented place.

Treat microgreens as house plants. They should be enjoyed for their beauty, nutrition, and flavor as they grow!

Last Two Thoughts

Remember to Do This and Less is Best principles; you will have beautiful microgreens. 

We hope you found this how-to water microgreens article and video helpful. If you have any questions or comments, please leave them below.