Why Grow Hydroponic Lettuce Indoors – When It’s Snowing Outside


As I look out of my window of my home in the middle of March we still have lots of snow on the ground, its -6 degrees Celsius that’s 21 Fahrenheit for those who live south of the Canadian border. I smile as I look at my hydroponic system and think, now I know why I grow hydroponic lettuce indoors.

The seeds came into our Wal-Mart store back in February and according to our Farmer’s Almanac the last frost will be the second of June. Now, that’s a lot of advanced growing time I can get in. Even with the greenhouse, unless it’s heated, there’s always a risk that frost may get them.

Why don’t you try your hand at growing lettuce or spinach hydroponically. It’s much easier than you think. It’s quite easy to make your own hydroponic system and it does not have to be expensive, though I’m sure you will want to build or buy a much larger unit once you get started.

See my page on “Build Your Own Hydroponics System” to get you started.

Other than the small system that I built I have a 12 pot system that I purchased a few years ago and it’s still going strong. The nice thing about lettuce or spinach is you don’t have to harvest it all at once. If you have a few plants growing you can nip off a few leaves from each plant as required.


Early Great Lakes Lettuce
Early Great Lakes Lettuce

Early Great Lakes Lettuce.

This is the one that I am growing from seed.

Once you have chosen the lettuce you want to grow there are several ways you can start them from seed.

  • The best way is to use Rockwool 1 inch starter plugs, this the most common way to start seeds with Hydroponics. You can start them with the Rockwool right in the net pot or in a seed tray with a plastic dome over the top.
  • Another way is clay pebbles. You can just sprinkle the seeds right onto the clay pebbles in the net pot, making sure that the water wets the pebbles and the seed are not floating in the water.
  • Also peat pots that are used for outdoor gardening. I found that they work just fine and are okay if I can’t get the Rockwool starter plugs.

Which ever method you use you can cover the seeds with a clear plastic cup that will act like a greenhouse to keep the humidity in.

What no soil?

Picture of a Net Pot
Typical Net Pot

Let’s talk a little bit about the growing medium because here we have a few choices. What you use, purchase or have readily available will mainly depend on what can be found in your area. Also the size of the net pots you are going to use in your system will determine which medium to use. Net pots come in variety of sizes from 2 to 4 inches.


The grow medium that can be used are:

  • Clay Pebbles
  • Vermiculite
  • Gravel
  • Pea Stone
  • Perlite
  • Coco Fiber
Clay Pebbles
Hydroton Clay Pebbles

The small clay pebbles is what I use also called Hydroton  which is the trademark name. I found them to be excellent and can be used over and over again. Once used I wash them and the net pots in a solution of water and hydrogen peroxide and they are ready to go again.

Some people use bleach as a cleansing agent but Hydrogen Peroxide does the job without the bleach smell. I usually guess the amount of Hydrogen Peroxide as I pour it from the bottle. About a quarter cup per gallon of water.

Good nutrients are the key to healthy plants.

There are more hydroponic nutrients available than you can imagine and everyone who is doing hydroponics has their own personal favorite.

When plants grow in soil there are nutrients and elements in the soil that help convert the fertilizers to something the plant can assimilate. There is also have worm poop that adds other nutrients to the soil.

Growing plants without soil means that you have to find a nutrient formula that will substitute what the soil and fertilizer provides. There are something like 20 nutrients, elements and trace elements required to make a plant grow healthy. A good nutrient formula designed for hydroponics is essential for healthy plants.

The nutrient formula that I use is DNF Gro and DNF Bloom. These were developed in Holland and has been around for over 25 years. If I grow lettuce which is a leafy vegetable I would only use DNF Gro. Other plants that need to bloom before fruiting like tomatoes would need the DNF Gro and DNF Bloom as the plants develop.

Miracle Gro for Soil
The above is for soil only – Do Not Use in Hydroponics.

I’m told that ‘Miracle Gro for Hydroponics’ works well although I haven’t used it. Make sure the Miracle Gro you use  states that it is for hydroponics and not for soil. I have read on the internet that Miracle Gro for soil may be toxic when used in a hydroponic system. It has a Caution label saying only to be used as directed because of the Magnesium and Zinc levels. This product will do a great job in soil because that is what it was designed for.

I have ordered the Miracle Gro for hydroponics so I can do a review on that later.

Why Grow Hydroponic lettuce as a starter crop?

Lettuce is an easy starter plant to grow and good for the beginner.  It likes cooler temperatures and  will germinate anywhere between 5C° (40F°) to 29C° (85F°) the best being an indoor temperature of 21C° or 70F°. There is nothing worse than failure to discourage you when you start something new. I feel that growing lettuce will build your confidence in growing food without soil.

Spinach takes much longer to germinate and sprout which can be anywhere from 7 to 21 days. Because of the long germination period you may feel they are not going to grow. So always refer to the package for germination times.

My lettuce package says 7 to 10 days to sprout and sow 1/8” deep. The seeds need light to germinate that’s why they are only planted at a 1/8″ depth. I usually put 3 seeds in the growing medium and when they sprout and grow with two or three sets of leaves I would remove the two weakest plants leaving the strongest plant to grow.

Aah… your lettuce is growing nicely. Now would be the time to keep your eye on temperature because warmer temperatures may cause the lettuce to bolt and go to seed, this also make the leaves tough.

To have a steady crop of lettuce you can start your seeds a week or two apart, this will give you fresh lettuce all year long.

What about pH testing?

Lettuce requires a pH balance of around 6. Oh no! Do I have to buy more fancy gadgets? If you don’t have a pH tester it’s not the end of the world. When I first started growing with hydroponics I did not have a pH tester and I grew a large crop of tomatoes.

All I did was keep the water topped up as it was depleted and change it out every 10 to 14 days so you are always starting out fresh. When you are doing the maintenance just make sure the air stones are working well to keep the oxygen levels up in the water.

To change out the water on my system I have a hose going into the bottom of the tank through a rubber grommet. I just bent the hose down below the water level to drain the tank into a bucket. But dont just throw that down the drain its also good to use on your other house plants. If you are building your own system you could fit an emptying valve on the side of the tank to make life easier. Then refill it with the right amount of nutrients and water.

Making the Days Longer

In the winter months the daylight is shorter depending where you live, so you have to compensate for the lack of daylight. To extend the daylight I use grow lights which are designed to give the right lighting spectrum for your plants.

When I first started to grow tomatoes I used a 400 watt Metal Halide light with a large reflector. It is not necessary to go to that expense when just starting out. Many people are using a 4 foot fluorescent fixtures with a couple of fluorescent grow light in them with success.

Lights in a power bar
Home made Lighting system

For a small home made system you can make up three light sockets with plugs on the end, fit them into a 6 outlet power bar and install three CFL (Compact Fluorescent Lights) Two at 4700 K for the white light and two at 2700 k for the softer more yellow light this will giving a good lighting spectrum range. Its is inexpensive and ideal for the beginner

You can pick all these parts up at your favorite Wal-Mart store or any hardware store.

You can then support the lighting power bar above the plants as you see fit, making it adjustable to compensate for plant growth. Keep the lights as close to your vegetables as you can without touching.  Some lights will burn your plants if they touch. Using CFL compared to other lights makes it much cheaper to run. For example if you run three 100 w CFL lights that would be equivalent to only 23 w each. Attach a timer to the power bar and setting it to increase the daylight time to anywhere between 14 to 16 hours. You should be good to grow… go.

Harvest time “Yahoo” you made it!!!

Harvesting your lettuce is the best and the easiest part. The great thing is you don’t have to harvest the whole plant at once. Just pick off a few outer leaf here and there and the inner leaves will quickly grow to take their place. No more soggy lettuce from the fridge just fresh crisp lettuce for your salad or sandwich.

I hope you had fun with this article and it has encouraged you to start your own hydroponic farm and grow your own food. The great thing about hydroponics is you can grow food on a balcony, a deck or just about anywhere. So what are you waiting for… give it a try!

If you have any questions or would just like to connect, please leave a comment below, thanks.

Happy Gardening!

John C



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