An Experiment in Growing Hydroponic Tomatoes

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Gardening has been a hobby of mine for a very long time. In fact before moving into the condo that I currently live in, we lived on 5 acres and I had a gigantic garden and greenhouse. Gardening can be a great maker experiment. From planting in the ground to raised gardens to pots. Choosing the seeds or plants. Watering systems. Tilling methods. It requires using the engineering design principle. Trial and error. Taking a risk. And then if your garden fruits, you have to determine what to do with the harvest. Crack open your cookbook and pull out those jars, you can learn to can your produce. Or freeze it. Or use it up. Or sell it. Or give it away. Or trade it. Moving into the condo required me to downsize my quarter acre garden and get creative. At the same time that I moved, I had been dabbling in hydroponics in our Maker Space at school. I got excited about doing hydroponic gardening at home and that’s what I did this past winter.

With the weather warming, it is almost time to shut down the hydroponic operation in my basement and focus on planting outdoors. One experiment I’m trying is to compare the growth of tomatoes grown hydroponically with those planted in soil. I began the tomato seeds on March first and have since transplanted them once. Three tomatoes were transplanted in deli cups and a fourth was transplanted in a five gallon bucket with perlite as the growing medium.

I have tried to treat the four plants the same with keeping them outside and giving them water. The difference is that the plant in the five gallon bucket receives a nutrient solution 4-5 times daily poured from a reservoir. As the unused nutrient solution flows down through the perlite it returns to the reservoir through a drain so it can be re-poured at a later time.

I expected that the hydroponic plant would do much better than the plants in soil, but this has not happened. As of this morning, the plants in soil are about two times as large as the plant in the bucket. In about a week, I will transplant the soil plants to the outside. My guess is that they will experience some transplant “shock” and their growth will be slowed.

I am also wondering if the nutrient solution should be tweaked for the hydroponic tomato. I used the same formula that I used for growing lettuce in my basement under lights during the winter. I believe that because tomatoes need green growth as well as fruiting growth that it may be necessary to add more phosphorus. The nutrient balance I am using is 19.5 – 18 – 38 so all of the nutrients are there. I am also wondering if the concentration is correct.

I just got an E.C. meter to test the conductivity so I will need to learn how to use that. I’ll keep you posted but for now, more study is needed. See what I mean about making and gardening as a perfect maker experience!

Hydroponics 101.4: Light Requirements

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I’ve been growing plants using hydroponics for a few years now, both at home and in the classroom. For the first several years of doing hydroponics and aquaponics systems, I used a bank of T-5 fluorescent bulbs and they worked okay. But in this last planting, which I have set up in my basement, I purchased a bank of LED lights. I am passionately green and I read that LEDs are much more energy efficient and last much longer than any other type of bulb. I also read that LEDs can be tailored to provide the exact wavelengths of light for plants and flowers. You see, plants love light from the blue and red ends of the spectrum. While fluorescents provide some of that light, much of a fluorescent’s light is white and that is a waste of energy because plants use very little white light.


We’re currently in a series exploring Hydroponics {read our previous entries 101.1, 101.2, 101.3}.


The bank of LEDs was about $275 dollars. This was comparable to the cost of a T-5 bank of fluorescent bulbs, but I was astounded at the small size of the LED bank!

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I was blown away by the light though! What the LED bank lacked in size, it more than made up for in intensity. The instructions stated that the light should be hung at least 24 inches above the plants. I was able to hang it at about 22 inches. I was stunned that the light covered an area of about 2×4 feet where the plants were located. This from a bank of lights that is five inches wide and 18 inches long! My fluorescent bank was 22 inches wide and 46 inches long.

I left the light on while I worked in the basement. After about 15 minutes I started to see everything in a green aura. The intensity and wavelength of the light was affecting my vision. I decided to turn off the light and construct an enclosure around my plants that had Mylar reflective material on the sides to reflect the light back on to the plants.

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My plants are now bathed in blue and red light and are growing wonderfully.

Oh, and my vision is back to normal.

Hydroponics 101.3: The Circulation Method

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Picking up where we left off in our Hydroponics series… The circulation method of hydroponics is ideal for you if you have a few more dollars to spend (as compared to the more limited Kratky Method) and you would like your students to make a hydroponic system in the classroom. It is a great way to integrate the engineering design process and STEM into your curriculum as well as offer authentic learning to your class. It also offers you a way of integrating principles of chemistry and physics into your curriculum.


 

We’re currently in a series exploring Hydroponics and Aquaponics.
{Read the previous entries here Hydroponics 101.1 and Hydroponics 101.2}


 

In the circulation method, you need to provide a nutrient trough for the plants to bathe their roots in. This can be done in many ways. Two methods that I have worked with are a floating bed system and a rail system. With both systems I had great success.

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With the floating bed system, have your students construct a sturdy box of 2×4 lumber about two feet wide and four feet long. Attach a piece of plywood on the bottom and drill a hole for a bulkhead attachment to allow water to drain from the bed to a reservoir below the bed. Next, place a rubber pond liner inside the box and cut a small hole in the liner to match up with the hole you drilled earlier. Screw down the bulkhead and tighten it so that water will not leak out of the box. Now cut 2 inch holes into a piece of ½ inch thick pink Styrofoam insulation board. I used a 2 inch circular hole saw in a drill bit and ran the drill BACKWARDS so that the Styrofoam was not shredded.

Circulation-Method2

Now you are ready to fill the reservoir with water. I use a large plastic container (about 25 gallons) with a small aquaponics pump on the bottom and a hose running up to my growing bed. I fill the reservoir with water, add my nutrient solution, turn on the pump and circulate the water. Monitor the water height in the bed so that when you add your plant cups their roots are touching the water. I also would recommend you add a PVC pipe below by attaching it to the bulkhead with a PVC fitting so that water flows back to the reservoir.

Next we’ll explore light requirements, planting and monitoring your system.

Hydroponics 101.2: The Kratky Method

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Hydroponics gives your students an opportunity for hands on, authentic learning that is novel, STEM related and gives them a chance to tinker. We’re currently exploring Hydroponics and Aquaponics in a blog series (read Hydroponics 101.1).

Choosing the container that you wish to use for your hydroponic system is crucial. There are two ways that you can approach this. You can either place your plant in a container that has no water and nutrient movement which is Kratky method) or you can re-circulate the water continuously using a pump and aerator. Which method you choose depends on your space and budget.

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With either method, you should begin your plants two to three weeks before transplanting them into your hydroponic system.

In the Kratky method you mix your nutrients in water and fill a container. Next, you prevent light from shining on the solution by duct taping or painting the container, then you cut a hole in the top of the container for your plant basket and you set the plant into the container with some of the roots not immersed in the liquid so they can get oxygen from the air. The upside is that you can grow lettuce and quick maturing plants in about 30 days. The downside is that the nutrient solution will run out or will begin to smell after about a month because no aeration of the solution takes place. This method is simple.

It is very important not to let light hit the solution or algae will begin to grow and use up all of the nutrients meant for your plant. This method is great for windowsill gardens or in small spaces that receive sunlight most of the day.

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I’ve noticed some differences with each method. First, root development is much greater in the circulation method and plants do grow a bit larger (see photo comparison). Secondly, the nutrient solution can be used for a longer period of time due to aeration. I have eaten my lettuce from both systems and both salads tasted very good.

Next week I will tackle a circulating system. But before then we’ll be posting on adding fish to our high school aquaponics system!