Introduction: Kratky's Non-circulating Hydroponics
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! :)
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2 years ago
Is there a set spacing requirement for the holes where the plants go in? I'm planning to start one indoors, but for my tiered rack, size wise it's better for me to use a couple of 28 Qt (24 x 16 x 6) underbed container vs the 41 qt in your instructable. Think I can do 6 or 4 holes for that size? Or it's really dependent on the type of lettuce I'm going to grow?
Also instead of the 7-8 gallons in your 10 gallon container, would I fill up to say 5 gallons only in the 7 gallon container?
Or is there some formula I can go by for the spacing and water ratio?
2 years ago on Introduction
I was thinking, instead of Installing the tube to check the water level, why not tape off a 1” vertical area on the side of the plastic water container? Sticking tape over the clear area,so you can lift off and check when you need To. Wouldn’t that work?
Reply 2 years ago
That would work... we stopped using the water gauge all together. Now we just lift the lid 😉
3 years ago
It should be pointed out that you need to maintain a proper temp. of the nutrient solution. 65-80 is generally said, but for Lettuce i would say between 67-73. I believe anything over 68 F can start to breed diseases , although growing at 72 (for example) certainly doesn't mean you will get any. Just that it might be easier for them to develop. In any case, you'll need to maintain/monitor temps. at all times. I use aquarium thermometers in my reservoir(s) to monitor.
Question 4 years ago
I live in a small apartment, but still have some space I don't use. I've been thinking of getting a grow tent to do some hydro gardening and make use of the space. Going to use the Kratky method and hopefully not refill tanks often. Plants I'm thinking about are cucumbers, tomatoes, peppers etc. How much water volume is needed per plant? Would one 35l (9,25 gallon) jug for each plant be enough? Don't want to go much bigger then necessary because of limited space.
5 years ago
When I tried the Kratky method in a mason jar a few of my herbs did fine, but a few of them seemed to absorb the nutrients leaving the reservoir almost empty within 3 days and the herbs wilted.
Question 5 years ago on Step 8
Will 10-8-22 nutrients work for all types of vegetables and herbs?
Question 5 years ago on Step 2
Is the above shelter with the clear corrugated supported by PVC? Just wondering because it looks like it may be.
6 years ago
if one grows tomatoes, after they've given their "fruit" will/do the plants die or if water+nutrient solution is maintained steady they can survive for years? (noob here lol)
Reply 6 years ago
From what I understand about tomato plants, they are actually perennial rather than annual. They are grown and assumed to be seasonal because of the change in weather. That said, every cycle of production from the plant yields less than the one before. We keep our plant going, in Hawaii, until it dies of something like infestation or disease and then start over. Also, we moved our tomatoes and cucumbers into 32 gallon garbage cans, there's enough water that we only have to refill twice while the plant is producing and it's very convenient, the brute cans use a food grade plastic. Let me know what you experience!
6 years ago
Okay, thank you!
6 years ago
Thanks for a very informative post.
I now realise the mistakes i have been making with my hydroponic experiments.I still have some questions.
1.What difference will it make if we use any other nutrient formula say
9-9-9 NPK or any other.
2.How does the lettuce perform in open? Do we need to cover and isolate the growing containers/ area with a plastic sheet or net.
3.Can we plant the seeds directly in the net pot or should we plant the seedlings.
4.If we start with seeds why do we need to keep some empty space in the container. Why not fill it up completely till it touches the bottom of the net pot.
5 How can we grow lettuce if the outside ambient temperature is above 40°C.
Reply 6 years ago
Hi, sorry for the delayed response... For the nutrient, a 9-9-9 NPK is a base formula that you augment based on what you are growing. You should find nutrients specific to vegetables and/or fruit and you should not compromise quality. I grow my lettuce outside, under our house eaves, you'll want to prevent rain water from diluting your nutrient solution. I plant my seed directly in the net pot all the time. You should absolutely fill your container with nutrient solution to the net pot so that the moisture and nutrient reach the seed. Only when refilling do you fill it up part way so that the roots can take up oxygen and not drown. I'm not sure how the lettuce will do at that temperature, but my guess is that it will grow more like a vine than a tight cluster (still edible) and you will have to refill the nutrient more often. One more thing... I've changed my growing medium to cinder and am much happier with the results... No algae!
Reply 6 years ago
I will keep in mind your advise while experimenting.
How to find which nutrients are specific to different crops.
PLS suggest nutrient for
Can I buy say NPK 20 20 20 And then modify to suit the specific type.
Reply 6 years ago
Please reference the pictures of nutrient included in this instructable for more information regarding nutrient ratios for specific plants. If the answers to your questions can't be answered from what I've provided please consult your local university's horticultural department, a hydroponics retailer, or a company that manufactures NPK.
8 years ago on Introduction
Okay, so I've done outside circulating Hydroponics for a few years during growing season. I live in mtns. of CA (inconsistent temps from 70 deg. down to teens) so can't do winter outdoors. What temp do these lettuces need in order to thrive? Trying to figure if I can do small greenhouse or need to do indoors. Thanks for the system, it looks great!
Reply 6 years ago
You can totally do this indoors!
Reply 8 years ago on Introduction
Most lettuce types do not do well over about 75 degrees and can tolerate temperatures as low as 45 degrees, so a greenhouse might be an option for you if the night time temps in the greenhouse do not drop too low. I live in Southern California and have trouble growing lettuce because sometimes the temperatures are too high and the plant bolts quickly. A cooler area of California with a greenhouse seems ideal to me. Some types of lettuce like romaine can tolerate more heat but in my opinion its always a much tastier crop if you can keep the temperatures in the 70's. Good Luck!
8 years ago on Introduction
So basically how it differ from other hydroponic measures is that you don't change the water but just replace the plant when it runs out? Would the plants absorb all the nutrients in the water in like a month?
Reply 6 years ago
The ratio I use is one gallon of nutrient water per head of lettuce--usually one month to six weeks. You can just start over with new seed once the water has been used up or you can refill half way if the plant has more to offer.