Growing Hydroponic Lettuce Indoors [The Ultimate Guide]

Are you thinking about growing hydroponic lettuce indoors? I will show you how to grow lettuce indoors. I am growing a mix of Buttercrunch and leaf lettuce.

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Growing Asparagus Hydroponically

Are you thinking about growing hydroponic lettuce indoors? I will show you how to grow lettuce indoors. I am growing a mix of Buttercrunch and leaf lettuce.

Growing Hydroponic Lettuce Indoors

Start growing hydroponic lettuce indoors with the Kratky method. It is a passive form of DWC, needing no airstones, pumps, or electricity. It is cheap and easy to set up. Lettuce is fast growing and a good choice to grow indoors because it needs less light than many other crops.

Kratky Hydroponics DIY

To start growing hydroponic lettuce indoors you will need to build a simple Kratky system. Don’t worry it is really easy.

Material List

  • You will need a tote and lid, any size will work.
  • You will need some 3 inch net pots.
  • You will want a 2 7/8 hole saw, otherwise you will need to trace out the holes and cut them out with a razor knife. (not recommended)
  • Some hydroton.
  • Lettuce plants or seeds

Your tote can be any size but it should be opaque. If it isn’t cover it or paint it black. You want a tight fitting lid. You will need to decide how many pots you want and trace them out.

The lid on my 10 gallon tote is about 15 by 20 inches and I cut out 12 holes about 4 inches on center. You can go a bit wider if you want but not any closer. Measure twice, cut once.

The net pots are not a full 3 inches so you want to use a 2 7/8 hole saw. The pots will fit perfectly. If you go larger they will fall through. Here is what mine looks like:

Kratky Lettuce Easily Grow Lettuce With A Kratky Method Hydroponic System DIY

You can also see the jiffy pellets I planted my lettuce seeds in.  You can use starter plugs like Root Riots too.

You will want to fill your Kratky with water and nutrients about an inch above the bottom of your net pots.

Water is heavy, about 8 pounds per gallon. So you will want your tote in its final position before filling it.

That is it! You just built yourself a Kratky for lettuce. Congrats!

Starting Your Lettuce Plants From Seed

Start your seeds in jiffy pellets or starter plugs. Plugs are really better but use what you have. Don’t try to start your seeds in soil because you don’t want loose dirt falling into the reservoir.

I am growing a mix of buttercrunch and leaf lettuce in my tote. Buttercrunch will make loose heads while with leaf lettuce you can pick individual leaves off for a more continuous harvest.

I planted a mixed pack of leaf lettuce so I have 3 or 4 different kinds. Put a few seeds in each planter. They are small and you want to make sure each planter has at least one healthy plant.

Once they sprout you can thin them out or leave them until they get a bit bigger for an early salad.

How To Start Lettuce Seeds

You can start your seeds in a damp paper towel by folding them over. Set the towel inside a small plastic container with a lid.

Put it in a warm place for a few days. It doesn’t have to be dark. Unfold the paper towel to check on them.

Once they show signs of sprouting transfer them into your peat pellet or started plug.

Starting Your Lettuce Plants From Transplants

If you buy plants from a garden store you can save several weeks of time. You don’t have to worry about germination and seeds are slow to start growing. You will get a crop sooner this way.

But you cant plant them the way they are. You will need to gently wash away as much of the soil as you can.

Setting Your Hydroponic Lettuce Plants In Net Pots

You will want to set your plants in the net pots and backfill around them with hydroton. You can use perlite too or even gravel as long as it is clean but hydroton or growstones work best. 

The plants don’t really grow much in this. It is there to support the plants and block light coming through into the reservoir. You do not want light getting in the reservoir.

The Kratky Method

So I am growing my hydroponic lettuce in a 10 gallon tote but you can use one smaller or larger.

Some growers use a piece of floating Styrofoam cut to fit inside their tote. This is called a lettuce raft. A lot of commercial lettuce is grown this way.

The roots in the water are feeder roots. They send nutrients up to the plant. The roots that are above the waterline become air roots that supply oxygen to the plant.

But I like to cut holes in the lid of my tote instead. Styrofoam can be messy to work with and it can let light into the tote along the edges.

The Kratky method uses no pumps or airstones. Normally you fill the container at the start and when the water runs out the grow is done.

For this reason, it is best for small fast growing plants like lettuce.

If you wanted to grow tomatoes in this system you would need to grow them in a trash can. Not very practical indoors. But I found a workaround.

My Modified Kratky System

Here is a picture of the roots in my modified Kratky system. You don’t need to make any modifications to your Kratky. It is fine as is.

Hydroponic roots

I decided to add airstones to mine. I also added a wick system to it. Neither is needed but I think there is an advantage to adding airstones. I added the wicks to move water up to the pots as the water level drops.

Growing Hydroponic Lettuce Indoors In A Hybrid Hydroponic System

My system started out as a standard Kratky method grow. But I decided to hot rod it a bit by adding airstones. One reader pointed out that with the addition of airstones it now would be considered DWC.

But I did something else. I added wicks to each pot. So it might also be called a sub irrigated planter or SIP.

So I guess it is in a class of its own. That is why I call it a hybrid but as long as it grows lettuce for me I don’t care what it is called.

Normally you fill your Kratky system once at the start and just let the level go down naturally. The crop is done when the water is gone.

If you try to refill it you would damage the air roots it has developed.

But I wanted to be able to top my reservoir up and adding airstones allows me to do this. This also allows me to grow a larger, slower maturing plant as long as I keep it topped up.

With some aeration, the air roots won’t be damaged because they can breathe even if partially submerged.

You can just set up a simple Kratky lettuce grow or you can adopt some of my modifications if you want something a bit more complicated.

How many hours of light does hydroponic lettuce need?

How much light does lettuce really need? Some people say 16-18 hours a day because that is how much light they get outdoors. But they also go to seed with long daylight hours.

I give my lettuce 10-12 hours of light from a LED grow light. They grow fine. My electric bill is lower and they will be slower to bolt and go to seed.

How long does lettuce take to grow in hydroponics?

Lettuce is a fast grower. You can probably start harvesting leaf lettuce in 3 or 4 weeks. Heading lettuce takes longer to finish but can be done in about 45 days.

If you start plants with seeds it will take a few weeks longer than starting with transplants.

You can buy transplants at a garden store but it is very easy to start a new crop from seed every few weeks. Start them in starter plugs like Root Riots or in Jiffy pellets That way you won’t have to wash off the dirt like you do with store bought transplants.

Feeding Hydroponic Lettuce 

I recommend using hydroponic nutrients to feed your lettuce plants. Lettuce can be fed at about 600 ppms and a pH around 6.

You should really have a TDS meter and pH pen to measure your nutrient solution. Otherwise, you are just guessing. But generally, you can use half the manufacturers recommended feeding amount.

You can use a pH test kit. It is not that accurate, but it will tell you if you are in the zone. 

I would recommend using House And Garden Aqua Flakes because it is easy to calibrate without a meter.

It is a 2 part A+B hydroponic nutrient. And 1 ml each of both A and B is about 100 ppms.  So, for example 6 ml of each per gallon would make a gallon of 600 ppm nutrient solution.

Does hydroponic lettuce keep growing?

If you are growing leaf lettuce you can harvest individual leaves instead of cutting the whole plant. So it will keep growing and provide multiple harvests. But eventually, over time the plant will go to seed or become bitter.

If you want a continuous harvest you should start more plants every few weeks. That way you can harvest and replace plants periodically.

What’s the best lettuce to grow hydroponically?

Leaf lettuce is probably best. There are a lot of different varieties and colors to choose from. You should be able to start harvesting sooner with leaf lettuce.

We don’t usually grow true head lettuce like Iceberg in hydroponics. Besides those blanched heads have very little nutritional value. Buttercrunch makes small loose heads and is a good crop to grow.

Growing Hydroponic Lettuce Indoors Final Thoughts

Lettuce is a fast growing plant. It is also easy to grow. It is the perfect choice if you are just starting out with hydroponics.

The Kratky system is the ideal hydroponic system for beginners. It can be totally passive and doesn’t need electricity to work. It is also low maintenance so as a newer grower you won’t have to do anything but watch it grow!

Growing Hydroponic Lettuce Indoors Update

My hydroponic lettuce has really taken off. Plants were thinned to one per pot and two weeks later the remaining plants just went crazy.

Growing Hydroponic Lettuce Indoors

You can even grow lettuce in quart mason jars with the Kratky method. Here’s how:

Mason Jar Hydroponics Kratky Method Mason Jar Lettuce [ Easy ] (indoorvegetablegrower.com)

Here is some more info on the Kratky method:https://en.wikipedia.org/wiki/Kratky_method