Hydroponics in the Winter Greenhouse

This time of year I get really anxious for spring so I can grow more of my own produce. Eating healthy can be expensive, especially in the winter. Yesterday I bought a bunch of kale (no, not a whole bunch, just one bundle) for nearly four dollars. This makes for a pretty expensive habit when I use nearly the whole thing in my morning smoothie. It is for this reason that I built a greenhouse last fall hoping to grow more of my own greens throughout the winter.

My Winter Greenhouse

So I'd like to share some things about having a winter greenhouse. First of all, I live in North Central Washington State where the winters can be pretty cold and gloomy  for days or weeks due to inversions that form during the shortest days of the year. Temperatures can be below 0 F. but are usually more likely to be in the teens at night and 20's or 30's during the day. This winter was no exception as we probably had about average temps for our location.

I completed my greenhouse last October in hope of having greens all winter long. Having had some coldframes going for the last several years, I realized that the key to having greens during the winter is getting them started early in the fall so that, when the weather gets colder and the daylight hours are short, you are able to still glean some fresh greens from time to time as things just don't have enough daylight to grow much during December and January.

Winter Cold Frames

So I was able to take a couple of large trays about 20" x 40" and maybe 3" deep and plant them in late September in anticipation of putting them in my greenhouse when it was finished. I rooted some cuttings from my garden tomatoes as well just for kicks. Upon completion of my greenhouse, I realized that I had plenty of space so I decided to plant some spinach, collard greens and kale, each in their own container.

Well the winter started out pretty mild and I had some good results from my plantings. I was able to pick greens from the large trays several  times for a few salads and the other greens seemed to be coming along nicely.

Trays of Greens

In December, the weather turned cold and cloudy and my greenhouse went from having sunny days and 75 degree temps to cloudy days and 50 degree temps. Things almost quit growing altogether. I had to put a space heater in there to try to keep things from getting too cold. I even tapped into our central heating system to pump some warm air into the greenhouse (thank goodness it is attached to the side of the house!). Even with all this, temperatures got a little colder each night until it was getting down to 40 degrees at night and only warming to 50 degrees on cloudy days. The thermal mass of 20 five gallon buckets of water  was not able to warm up enough to make a difference and probably even kept things a little cooler during the day in spite of possibly moderating the temps somewhat at night.

I knew this would be a year of experimentation so I had to ask myself what I could do to get more production from the winter greenhouse. My initial goal was to keep things simple and inexpensive but I'd already cheated by using a heater and pumping heat into it from the house. I thought about purchasing grow lights but decided that the cost of setup and electricity would be more than I wanted to deal with my first season. This is when I began to experiment with hydroponics.

Hydroponics in a nutshell is the process of growing plants with nutrient rich water in a soiless medium. Given this definition, there are all kinds of options for how to set up a hydroponic system in a small scale greenhouse like mine. I didn't want anything too complicated so I started with a simple system called deep water culture (DWC).

 DWC is really a pretty simple system for anyone to set up. My setup consisted of a five gallon bucket and an aquarium air pump and airstone. I made four three inch holes in the bucket lid for my plants which were placed in plastic cups full of gravel (actually, three holes were for plants and the fourth was for me to insert the air tube and airstone)and later an aquarium heater). I melted quarter inch holes in the cups to allow the water to circulate through the rocks and to the roots. I placed the airstone in the bottom of the bucked, filled the bucket with water and a light solution of Miracle Grow fertilizer to about an inch of the top. I then put the lid on and placed the plants in the holes so the roots were about halfway in the water and turned the pump on. The principle of this system is simply to aerate the water so that the roots don't drown and plants really thrive.

DWC System

With this setup, I had another bright idea which was to heat the water in the bucket with a submersible aquarium heater. The hole for the air tube was big enough for me to insert it into the water. After all, it was easier to heat five gallons of water than it was to heat my whole greenhouse. My plants began to grow and the roots soon were poking out of the holes in the cups into the water below. This was pretty amazing yet  I was realizing that this system would only grow three plants and I really wanted a system that would produce enough plants to make a difference in my grocery bill! After further research, I decided that I could upgrade my hydroponic system to a nutrient film technique system (NFT) and grow even more plants.

In a NFT system, a shallow flow of water with a hydroponic fertilizer added moves across the roots of the plants which are in some sort of a tray or trough placed at a slight incline.  A pump is used to pump the water from a reservoir at one end to the other end where it gently flows across the roots via gravity back to a reservoir. This process constantly recycles the water providing roots with ample access to nutrients and water for efficient growth.

I scrounged around and pretty much found what I needed for this system lying around my house. I already had the reservoir, the air pump and airstone and the aquarium heater. I needed to add a water pump and a rain gutter and some plastic tubing, all of which I just happened to have. I did have to purchase the ends for the gutter which weren't too expensive. The submersible water pump went in the bottom of the bucket surrounded by a nylon bag to keep anything from plugging it up. The tube came out a hole in the bucket lid and ran along the ground to the far end of the gutter where it was placed through a hole so the water would run into the gutter and flow back toward the bucket. I drilled a hole in the end of the gutter so the water would drain back into the bucket to be recycled again and again. I did have  to add an in line valve to control the flow as it needed to be a trickle, not a gush.

NFT System with second gutter. Note that the spinach in the gutter was transplanted from the tote in the upper left of the picture. See the difference!

So within a couple of hours, I had my system set up as a new home for my three plants from the DWC system but I still needed another 25 or so plants to fill up the gutter and make full use of its capacity. And, rather than dealing with cups, gravel, melting holes and the wrong fertilizer solution, I ended up buying three inch net pots, hydroponic fertilizer and soiless medium (similar to pumice stone) from a local hydroponic supply store. The net pots are just small plastic pots which allow water to pass through them and over the plant roots. The roots ultimately grow out and along the gutter preventing plants from becoming root bound.

Since I already had some container spinach and collards in the greenhouse, I decided to transplant some into the net pots for my system. To do this, I gently removed them from the soil and submersed the roots in water to remove most of the soil. I then dangled the roots in the net pots so they were touching the bottom and placed the grow medium around them and base of the plant until each plant was supported. These went directly into the gutter where the flow of water would supply them all the nutrients for growth and hydration.

Nearly two months later, in spite of colder temperatures and short daylight I got some pretty amazing results.

NFT System

Now that it's February, the days are getting longer and we are getting some pretty sunny days. The plants in my hydroponics system are over twice as big as their siblings left in cold soil. I think the hydroponics helped but also believe that the warm water on the roots made a huge difference

Non Hydroponic Collards

Hydroponic Collards

Non Hydroponic Kale

Hydroponic Kale

Hydroponic Swiss Chard

I am realizing that this system will be great for this spring and I have even added a second gutter to further increase my production. I may even be adding more gutters soon and am planning on a somewhat different system this summer for tomatoes and peppers that I hope to be eating well into the winter months. And who knows what it will evolve into next winter, but I have hopes of more greens and smaller grocery bills in the future.