Growing Hydroponics Lettuce: Cheap DIY


May 9, 2015

A few weeks ago I started an experimental grow without any fancy equipment. No discount storage boxes or bins. I’m using recycled coffee tubs. This is really cheap hydroponics, DIY setups that anyone can handle making. Aside from the seed, I think I have about $1 invested per plant.

No, I’m not using a grow light, because I want to see just how well the plants do in a south facing window that has no light obstructions from early morning to late evening. I waited until the sun shone more than being hidden behind heavy winter clouds. Been there. Done that. It’s not worth the effort. So, we’re taking the new window for a spin during the appropriate time of the year for harvesting enough sunshine to actually grow something leafy.

This is passive hydroponics, a method known as Kratky. There isn’t any circulation pump. It’s a super simple setup that you can put together in an hour or two. But first, you’ve got to start your seeds, which means you need a germination chamber, and some 1″ rockwool starter cubes. You can buy a strip of 24 for about $8 – which translates to 30 cents per lettuce you grow. Still cheap, and you’ll be ready to start a fresh crop with supplies on hand.

You have to soak your rockwool for 24 hours in water to get the pH to the right level. I used distilled water, but adjusted the pH with lemon juice to bring it from the 7.0 pH level that all distilled water has down to the recommended 6.0 pH. Once that’s done you’re ready to plant. A domed plastic clamshell with a flat bottom from the store is perfect if the number of grow cubes you’re starting will fit inside and close with a couple inches of head room above their tops. I used a cookie box that had a clear top and a black bottom. Good for soaking up the warmth of the sun!

Recycled Hydroponics: Lettuce Starts in Germination Chamber

Remove the plastic wrapper from around the rockwool cubes. Drop your seeds in the pre-drilled hole. Take a couple of paper towels and fold them to fit the bottom of your container. Add enough water to saturate the paper towel but not so much you’ve got standing water. Sit your seeded cubes inside the box. Close the lid, and sit it in a dark spot where not sunlight can reach it. After 3 days, check your cubes to see if you’ve got sprouts yet. Check on them every day from here on, it doesn’t take long for lettuce to germinate.  If you’ve got two up, you need to give them light, so get them in the windowsill inside your germination chamber. Seeds need no nutrients for at least two weeks. They’re fine with just the moist cubes and paper towel in the box. Keep the lid on it to maintain good humidity, and put it in a south facing windowsill – right against the glass. If your paper towel starts drying out, remoisten it – this maintains the moisture in the grow cubes just enough to keep your baby lettuces happy.

Once the seedlings are tall enough to touch the lid, it’s time to remove that part of your homemade germination chamber. Just cut it off – there’s plenty more free boxes just like that you can save from the trash bin for a new crop. I left my lettuces in that recycled cookie box for 3 weeks after they all sprouted. Incidentally, The seed was sown on March 27, and they finally went into hydro pots on April 18… BUT for a week before I ‘planted’ them I gave them half-strength nutrient solution. Not much. Just enough to re-moisten the cubes by dipping them in the nutes, and then saturating the paper towel with it. The cubes were redunked twice a day, and growth started happening faster.

DIY Hydroponics from Trash

Now you need 2″ net cups, which will cost about 25 cents each. Put them upside down on the coffee tub lid and trace around it with a marker. Make a slightly smaller circle far enough inside that so the net cup won’t fall through. Use an Exacto or utility knife to cut out the circle. Best to start a little farther in than you think it needs – you can always trim it back so the pot sits flush with the lid. Now mix up some grow nutrients solution. If you use a one-part kind like GroTek Solo-Grow or Botanicare Pure Blend Pro Grow you’ll only need 1/4 teaspoon per quart of water for seedlings, and 1/2 teaspoon once they start filling out until harvest.

Before you add your nutes to the coffee tubs, you need to mark a line where the bottom of the pot will sit once it’s all put together. You want to keep the nutrient level just above that line until the lettuces roots grow long enough to reach the moisture and nutrition below there. If it drops too low, you will have wilted plants! On May 6 only one of the 4 in my windowsill has roots that are out reaching out past the plastic net, but the plants are growing like crazy. Look how small they were when I moved them into the pots below. I’m using Solo-Grow, which is working out very nicely. So far, I’ve had to add nutrients twice… in 6 days.

Passive Hydroponics Lettuce

Notice that 2 on the left in the photo at the top of this page are larger than the other two? There’s a good reason for that. Another plant in a large pot was hiding them so I didn’t see what was happening until I checked the nutrient levels on the 5th. At first I thought it was because the larger two plants were getting light from the grow rack across the room til late at night. This might be part of it, but the bigger culprit is probably the center framing on the window panes themselves – it casts a shadow from mid morning until early afternoon as the sun moves across the sky. Time to rotate the pots every day to share up more sun energy! Better yet – take them outside during the day until the weather warms more where they’ll get lots more sun.

Best guesstimate on when this lettuce will be ready to harvest is in 4-6 weeks (it takes 3 months in the ground). They would probably grow a bit faster under a grow light, but that’s not part of this experiment. Since it’s working well, it’s time to sow another 4 seeds, and build up a steady supply of fresh dirt-free lettuce 😉


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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