A friend of mine, Ingrid, started growing her own lettuce mix at home using a non-circulating hydroponics system. I was very interested in what she was doing because it requires no electricity and only a one time nutrient feed. She sent me brief, but great, instructions and I did a little research on the Kratky method of hydroponics and decided to share what I've done.
These instructions are brought to you after six months of successful growing. Ingrid had been growing for a year by the time I gave it a try.
I've also attached a PDF file of one of Dr. Kratky's papers outlining his method and how it works... if you want to get all "sciency."
Step 1: What You'll Need
Underbed box 41 QT/39 L (approx 35" X 17" X 6") and/or 5 gallon bucket (I will be using both in these instructions)
Plastic paint primer and paint
1/2 inch x 1/2 inch elbow (optional)
Rubber grommet 3/4 inch OD x 7/16 inch ID (optional)
Clear vinyl tubing 1/2 inch OD x 3/8 inch ID (optional)
1/2 inch drill bit (optional)
2 inch hole saw
8 - 2 inch net cups per lettuce bed.
Strap to hold shape of container once it's filled with water
PH water testing kit
Hydroponic nutrient (your choice of brand)
Place to set up your lettuce beds
This setup should come in at under $30
Step 2: Where to Grow
Before you begin, choose where you will keep your setup, on a table with some indirect sunlight or under house eaves is best. Once the tub is full of water it is very difficult to move the system. You can also grow indoors under light if you want, I don't because I live in Hawaii and we have a year round growing season that allows me to use good ol' sun light.
Step 3: Time to Drill
With the Kraty method of non-circulating hydroponics it's important to remember that one gallon of nutrient water per plant is an optimal ratio when growing lettuce... so with the under the bed storage box I used, I drilled eight, evenly distributed, holes in the lid using the two inch hole saw. Use the utility knife to scrape off any plastic and smooth out the holes.
This box is a 10 gallon box, but I only fill it up to eight gallon so that there is a space of humid air for the plant roots to derive oxygen since this system doesn't aerate with mechanization.
I use this type of container for lettuce because the roots are shallow and I want a good amount of space for my plants to grow. There are other types of totes that hold the same amount of water, but the shape and depth aren't what I considered optimal for lettuce growing.
Step 4: Optional Water Monitor
I like to keep track of the water level in my reservoir, so I also drill a 1/2 inch hole on the side to insert a tube to monitor what's happening on the inside. If you decide to include this step you have to be very careful drilling the hole.
I think starting with a small bit and graduating to larger ones until you reach the 1/2 inch bit might be best if the plastic is stiff.
I've cracked the plastic a few times and had to use food grade plastic epoxy on the damage in order to use the container. It's not too big of a deal because you still need to paint the container and the repair will be camouflaged.
Step 5: Now for the Painting
Painting the box is very important because if sunlight reached the nutrient water algae will grow, eat the nutrients and starve your plants. Also, I would not recommend painting the boxes before drilling the holes because the paint could scratch off. I encourage you to use the primer, the paint seems to better adhere to the smooth plastic when you use the primer and follow the instructions on the can.
Finally, I would also recommend that you tape the holes you just drilled (lid and container) so that you can keep the inside of the box as clean as possible... this is where your plants eat after all!
Step 6: Optional Step Continued
If you decide you want to monitor the water levels this is where you insert the rubber grommet, the elbow and the vinyl tubing. The thing about this process is that everything is VERY tight so that water doesn't leak.
To get a snug fit with the vinyl tubing (and to straighten it out because it probably was coiled when you bought it), dip it in hot water and attach to the elbow and then hold the tube straight until it cools down.
Insert the elbow into the hole with the rubber grommet... be patient, this isn't going to be easy!
Should the grommet leak just use a little silicone to seal it.
Step 7: Measuring Your Reservoir
So now you've got your lettuce bed ready to fill. What I recommend is that you measure the water levels up to eight gallons so that you can use the garden hose and mix your nutrient right in the reservoir once you have it in place.
If you don't have the monitoring tube, fill the container up to four gallons and mark the inside with a permanent marker and then fill up to the eight gallons and do the same.
If you have the monitoring tube, mark the outside per gallon.
Make sure you do this on a level surface so that your markings are as accurate as possible. This important so that when you add the nutrients to your water it's the right amount of food for your plants.
**I should take the time to say that my husband thinks we should only fill it to seven gallons to created a bigger air gap between the lid and the water... I haven't noticed any negative results (such as drowning) with eight gallons.
Step 8: Now Adding the Nutrients
I use a brand called Chem-gro Hobby Formula 10-8-22. It's a powdered nutrient that I've been very successful using. Also, as I understand it, it is the formula Kratky used when developing this method. At first I was worried because of the word "Chem" in the title, but I called the company, Hydro Gardens, and they explained that it's just the brand name and that their product is not chemically altered and it doesn't have extra chemicals or anything like that... You can use any brand of nutrient you like, just follow the directions.
After you've added your nutrients to the water you have to test the Ph to ensure it's what is recommended by the manufacturer. The Chem-gro brand has buffers in it so the Ph is always spot on.
I found this to be an important step because I use city water and the Ph is 8.1-8.5 making the water too alkaline for the plants to take up nutrients. If you use rainwater this shouldn't be a problem.
Now put the lid on your new lettuce bed.
Step 9: Time to Plant!
Ok, you've found a location for your lettuce bed, assembled it, filled the tank and added the nutrients... Now for the fun stuff!
Fill each net cup with perlite and stick it in one of the holes you drilled in the lid. Eight gallons of water and eight net cups with perlite. Some people use a vermiculite/perlite combo, but I use 100% perlite... the preference is yours.
Place the strap around the middle to hold the sides of the container in place when it is full of water.
Seed cups with romaine, mesclun, arugula, cress, komatsuna, bok choy, chard, mustards... a few seeds per cup.
That's it... Watch them grow! If one does not sprout after a while yet all the others sprout, either move a double seedling or replant the cup with seed. You can harvest the outer leaves when they get big enough or cut the whole lettuce.
You could plant one tub and maybe two weeks later set up a second container. Ingrid's family of four eats big salads every night from one box a week, and my husband and I can eat from a box for two weeks.
I've also learned that when the lettuce bed has used up all of its nutrient water (because of heat or other unconsidered conditions), but you're not done harvesting, you can refill the container halfway with four gallons of nutrient water and keep going (that's why I marked the lettuce beds at the four gallon mark)...
I mix four gallons of the the nutrient in a five gallon bucket and pour it in (after I empty the rest of the water from the container of course!). The key to replenishing a reservoir you make of any kind is that you have to let half the roots remain exposed to the air so that they can absorb oxygen otherwise, your plants will drown.
I've also grown tomatoes in 18 gallon containers, cucumbers in a 32 gallon garbage can, okra in five gallon buckets (replenishing with 2 1/2 gallons of nutrient water as needed), and squash in 10 gallon containers using this method and have had great luck!
I'm also going to plant sugar peas and green beans in five gallon buckets... I'll update these instructions once I have results.
Oh, and thanks, Ingrid, for helping with my setup. You're the best! :)