Lettuce Not: Kratky Hydroponics DIY


June 20, 2015

Growing food in the windowsill has millions trying it, but not everything you read out there in blogland should be taken to heart… like growing herbs in tea cups. Cute, but not very productive. Recycling empty food containers is hot too, and I’ve seen the coffee can trick shown off on a number of sites, so naturally I had to experiment. At least this container is big enough to allow for some root growth. And so began my Kratky hydroponics DIY lettuce grow using the sun for light. That was in late March.

As you can see in the photo above there was no lovely large heads of lettuce to harvest, though the plants did grow very nicely for a while. If you haven’t read the first post on this grow, it looked very promising.

What Went Wrong?

Let’s start off with the fact that the Kratky method does work when done properly. I don’t think it’s particularly suited to this kind of setup though, unless you have nothing at all on your schedule but keeping an eye on your letti. Someone who works away from home will probably have crop failure faster than I did. I may be home all day, but I work long hours, and all manner of wilt can be happening in the windowsill before you remember to check on things… it’s not visible from the office.

The curly leaf lettuces never grew roots that could extend into the reservoir. Lots of top growth, but unless the solution level was kept up to the bottom of the net cup constantly, droop set in. Do you have time to check this situation 8 times a day? One was leggy, and one was not for reasons unknown, and the leggy one had less root growth than the other one even though it was twice the size! To the new gardener this might not be puzzling, because they’re just so ecstatic that they’re actually growing food. Stick with it awhile. Experience is a great teacher.

Don't Try This Kratky Hydroponics DIY MethodDo you have any idea what happens to the sunshine passing through window glass? It’s magnified… which is why glasshouses at fancy garden centers have shade cover on the roofs in summer to stop the sun from burning everything growing inside of it. Thermal pane windows might also increase this effect because there’s two layers of glass the light travels through. The southern exposure you need for efficient light in winter becomes brutal as the sun shifts position in spring. Now not only is the solution getting warmer, but the thin leaves of lettuce that’s fully hydrated aren’t designed to withstand those kinds of exposure.

So, in the end the best lettuce of the bunch was burned by the sun. The damage was on the leaf tips closest to the glass. And at that point I gave up, which is exactly what all the new indoor gardeners out there will do when your grow is such a pain to keep up with, and an exercise in futility in the end. The problem isn’t that you can’t grow stuff. Your thumb isn’t brown. You’re just approaching the project backwards when you attempt to grow in containers that are too small or poorly suited to the job. Recycling is great – when it works.

Now, if I had drilled holes in the bottom of these coffee cans and potted the lettuce starts like I would have for outdoor growing on the patio/driveway they would have fared far better. It would have been so much easier to keep them from wilting, but they still would have burned from the intense May sun blasting through that glass. Since lettuce has a compact root system compared to what you get above the soil, they wouldn’t have had root bound issues that some of those trendy growing ideas will produce.

Kratky Method Done Right

The reason that the Kratky method works is the right way to grow food with it is to plant it in a raft. It’s supposed to float on top of the nutrient solution, not be suspended above it. This hydroponics method is not suited to coffee cans. How would your grow go if the styrofoam is sinking down inside this little tub as the reservoir level drops? You either have to yank the float out by grabbing the plant by it’s leaves, or dump the whole thing out. Not practical for maintenance, and certainly a loss of sunshine for your plant, along with wear and tear on it’s leaves as it matures.

Things would have gone better if there was a wick, but that’s capillary action, not Kratky hydroponics. If your going to try this growing method, then get a tub so you can raise the raft without abusing your lettuces! No, it’s not cute, it’s not repurposing (unless you have one laying around), and you probably won’t find one in your trash can, but it works. A dark tub too with walls that aren’t transparent, so the sun can’t cause algae to grow in your solution reservoir.

It’s okay to get a jump on warm weather by starting such a grow out in a southern window, but once you hit mid-May… take your poor crop outside. That is if you want to eat that salad, because if you don’t you’ll morn the loss. Of course, if you had it growing under lights, this wouldn’t be an issue at all.

One last tip for you newbies out there. If you’re going to pot lettuces in a lightweight plastic coffee can and grow them outdoors, be prepared to anchor them somehow. Potting mix is light. A full grown, or nearly so, lettuce plant is heavy, and when the wind hits this setup it will knock over your pot. One way to avoid that would be to put an inch or two of gravel in the bottom, or a fist-sized rock.


Tammy Clayton

Tammy Clayton

Contributing Writer at Garden Culture Magazine
Tammy has been immersed in the world of plants and growing since her first job as an assistant weeder at the tender age of 8. Heavily influenced by a former life as a landscape designer and nursery owner, she swears good looking plants follow her home.
Tammy Clayton

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  • Carrie Khouzani December 18, 2019

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