We have finally finished construction on our aquaponic raft beds, also known as Deep Water Culture (DWC)! The system is up and running and we have hooked the raft tank in to the main fish tank, so the water is full of nutrients that drain from the grow bed and fish tank. We aerate the water with an air pump hooked up to air stones, and the plants’ roots hang down into the aerated water.
Even the children are excited, and got to help us transplant the first lettuces into the raft.
These beautiful red and green lettuce should be ready for market in 3-4 weeks.
When last we checked in with Mr. Greenhouse we were finishing up the structure, covering it with shade cloth, and outfitting the interior. That seems impossibly long ago, but it was only this past summer. Summer is long gone, and cold weather is here. There are two times when a greenhouse really comes in handy: keeping things cool in the summer under the shade, and keeping things warm in the winter.
Preparing for winter by removing the shade cloth and putting on plastic seemed easy enough—sure, we’ll just pull off the shadecloth, roll it up, and pull the plastic over. No problem! Ahem. It was a lot of work. Especially because the weather was preparing to change, and it had been windy for several days. We waited weeks for a calm day, and eventually decided to try it on a nice morning with just a hint of breeze. It was a beautiful day.
Getting the shadecloth off, truth be told, was a cinch. Just un-clip the sides and pull it off. The next job was to pull the plastic over. We bought a large roll of plastic, 55′ long and 44′ wide. It’s wide enough that the sides hang down to the ground to cover our tall windows. I tied a one end of rope to one corner of the plastic and the other end to a roll of duct tape, which I then tossed over the hoop frame.
We pulled and pulled, and inch by inch the plastic came up over the hoops. Amazingly we had no tears. We got it centered, and started securing the clamps along the side. That’s when the wind came up.
In spite of the wind (which was not much more than a breeze, but that much plastic acts like a sail on a sailboat), we managed to get the sides clipped down and secured. All was straight, tight, and beautiful with no tears or holes.
To attach the sides we used the Tube Lock base and clip that we procured from Greenhouse Megastore. On the ends walls we used the Spring Lock base and clip. After using both I can say I highly prefer the spring locks, and I won’t be using the tube locks again. The tube locks are very strong and look nice but they have a tendency to slice through the plastic if you put too much force on it. The spring locks will not harm the plastic and are extremely easy to install – just thread the spring lock into the channel of the base, and it holds everything very securely.
The sides are rolled up using a long pipe clipped on with fabric clips from FarmTek. We added a hand crank to the end of the pipe; while not absolutely necessary it makes opening and closing the sides quick and easy. On a sunny day the temperature inside can climb into the high 90s, even if the weather outside is cold, so it’s important to be able to open the sides to vent the heat.
Cold Weather Is Here
Now that cold weather is here we have the sides down most days. It’s cold outside (at least it seems cold to us Texans), but it’s nice and toasty inside. Without heat, on a cloudy day the temperature inside is usually 5-10° above the outside temp. On a sunny day it could easily be 20-40° warmer.
I’ve built out the inside with tables for seed starts and microgreens. We now have two separate aquaponic systems. In the photo below, you can see the four grow beds—two on the right and two on the left. The grow beds on the left are recently completed, and we’re cycling the system right now – it’s almost fully cycled! The ones on the right have been fully cycled for months, and are verging on becoming a jungle. We regularly have to go in and hack back the nasturtium. The tall plants that you can see growing up the frame are cherry tomatoes. Yes, it is December.
We do have many days and nights below freezing here, so we had a propane tank installed and hooked up Mr. Heater. It’s just a basic 30,000 btu blue flame heater, but its best feature is that it’s ventless, which means low installation cost. Last week when the temperature was below freezing for the entire week and all our outside water froze, the greenhouse was nice and warm and never got below 45° inside. While I like Mr. Heater, next year I’m hoping to look into warming the greenhouse using compost instead of propane.
We’ve set up a washing, cutting, & packing area in the back of the greenhouse. This is a wonderful addition because we can wash our hands right there in the greenhouse before working. It’s a wonderfully convenient place to harvest microgreens, and it’s easy to sanitize so that we can maintain high quality and good safety. Everything that we need to harvest and pack is right there where we need it.
Here are some of the things we have growing inside right now:
Raft Bed Construction
Our next project is raft beds for the aquaponic system, also known as deep water culture (DWC). Water will drain out of the gravel media grow beds, where it is filtered by the media, plant roots, and the nitrification process. Nitrification is the heart and soul of our system and what makes aquaponics work. That’s a topic for another blog post.
The raft beds are basically constructed like a deck, and then I’ll add strong sides and line it with Dura Skrim. We’ll then float “rafts” that will support the plants on the surface of the water. The plant roots hang down into the water and draw nutrients up from the water. We expect to be able to harvest many dozen heads of lettuce each week from this system.
The media beds are plumbed so that they can drain either directly into the fish tank, or out into the raft bed.
Here is a picture of our fish tank, showing the drain from the grow beds.
All a lot of work! And ongoing. We’re never short of things to do. But the end is nigh. After the raft bed is complete we plan to get good at growing greens, work on our consistency and quality, and reap the rewards of our labor for a while.
Then, on to the next greenhouse!
Thanks for reading. I will leave you with this, our aquaponic grow bed from an earthworm’s point of view:
Lately we have gotten the learning bug, and we’ve been teaching ourselves all about the soil food web, and the bacteria, fungi, arthropods, and other creatures that inhabit and enrich our soil.
Our latest experiment with different soils yielded some really interesting results.
About two months ago we planted tomato seedlings in two different types of soil, just to see what would happen. We planted two trays of tomato seedlings. Each tray was planted half with Miracle Grow potting mix and half with our own in-house mix consisting of coconut coir and worm castings. Being in the same tray, they were all watered and treated the same.
The photo below shows a stark difference between tomato seedlings planted in Miracle Grow potting mix (front) and our coco coir mix (back). All the seedlings in this tray are two months old—they were all planted at the same time. The six seedlings planted in Miracle Grow are only about 2-3 inches tall, if we’re generous. They didn’t amount to much. The five behind, planted in our seed mix are about 8 inches tall on average.
Six of the healthy seedlings were subsequently moved to pots, with more of our rich coco coir and worm castings mix. They have been watered with compost tea and dechlorinated water. They look really good, in my opinion. This is what you might reasonably expect to see after being transplanted to a larger pot.
Now look at the photo below. This is a plant from that same batch that was subsequently planted in our aquaponic grow bed. I can’t stress enough that this is from the same batch of seedlings, planted on the same day, two months ago. See the empty cells in the tray above? This plant is from those cells. There are several plants in this bed – all of them are over 18 inches tall.
For comparison, here is a fancy chart showing the relative growth of each of these different tomato plants. As you can see, the tomato in the aquaponic grow bed is out of control.
One of the key features of aquaponics is that it produces bountiful amounts of nitrogen, which probably accounts for the ridiculous amount of growth in the tomatoes planted in the grow beds. We are learning, however, that in spite of the amazing growth the soil food web in the grow beds is not quite complete. There are other nutrients that don’t seem to be present, or if they are, are not accessible by the plants, such as phosphorus. We have been adding compost tea, along with fungal, archaeal, and bacterial inoculants in the hopes that these microorganisms will flourish and begin to unlock the nutrients that the plants need to thrive.