My container garden project this spring would have gone a lot better except for two things. One, a weeklong period of hot sun with no rain really took a toll on the tomato plants, even though I set up a system to spray mist the foliage. Second, at some point, the critters started finding my plants– I must have thrown out over a dozen affected tomatoes.

Having my plants in a greenhouse would have– or should have– solved both of these problems. With the embarkation on my hydroponic system, I decided to construct a small greenhouse.

I found plans on the internet for a simple structure using PVC pipe to create a quonset hut-shaped “hoop house”. Covered with 6 mil clear polyethylene film and strategically placed shade cloth, it should keep out critters, control temperature, and retain moisture.

I decided on making it 9’x12′ since I have a slab extending my patio of roughly those dimensions that I rarely use. In that location, it will get good wind protection from the west and north, but it will still have to be anchored down to prevent any mishaps. With the addition of an exhaust fan and some venting, I should be able to provide an environment conducive to some vegetables, lettuces, and herbs.

I bolted together a frame out of treated 2x6s on-edge, nine by twelve feet, to fit on a section of my patio. 10 by 12 or even 12 by 12 would have worked using the same PVC and plastic sheeting. Using some mending plates, I made some L-shaped brackets to secure the frame to the slab.

The ribs are made from 3/4″ schedule 40 PVC, 10 foot lengths. Using 3/4″ crosses and tees, the ribs are joined together spaced 24″ apart. The top crossbar is from pieces cut 22-3/8″ (I think) to achieve the 24″ spacing once assembled. I did not use cement, but, in retrospect, should have, as one end joint worked loose over time from minor shifting in the wind. A 10 ft. length of 1/2″ electrical conduit inserted inside the top bar before the last end rib is installed aids rigidity. The ribs are secured at the bottom with heavy gauge pipe straps– I think you need to buy 1″ to fit 3/4″ PVC– on the inside of the 2×6 frame.

The cover is 6mil polyfilm sheeting from Home Depot. I have plenty left to re-do it whenever it becomes necessary– a roll 20 feet wide by 100 feet long was around $60. (What’s on there now still looks OK after nearly a year.) I made a dozen or so clamps from 1″ PVC by cutting slices 1-1/2″ in length and then removing a bit more than a quarter of their circumference, and sanding all sharp edges and points smooth. I applied the film on the ends first, wrapping from the inside, over the top of the end ribs, and making a short slit at the top center to fit around the top crossbar. Then a 13 by 20 foot piece went over the top, and both the end sheets and the top were secured by the same clamps at several points. Finally, the bottom of the sheeting was secured all around from the inside by folding it inward and screwing 2″ treated lath into the top of the 2x6s with the poly sandwiched between. Additional items included an X-shaped brace on one end to add rigidity, and a screen door made of treated 1x2s on the other.

You can get by in the winter months using a cheap box fan for airflow, but in the summer an enclosed hoop house such as this will need some serious ventilation to keep the temperature in line. Shade cloth alone won’t cut it. You might even consider making the ends out of screen instead of plastic.

While researching a problem I was having with my container gardening project, I ran across something rather interesting– hobbyist hydroponics. While I was aware of the concept of growing plants without soil– a recent visit to Walt Disney World had an exhibit featuring various hydroponic systems on a large scale– I was not aware how many people grow vegetables, herbs, etc, successfully on a small scale.

I found that there are several techniques to grow hydroponically, and that– compared to growing in soil– the results are fantastic. For example, the time from planting tomato seedlings to harvesting vine-ripe mature fruits is significantly shortened– from three months or more down to as little as eight weeks.

I decided to embark upon a new project, and build my own hydroponic system. I settled on a particular design that employed a hybrid concept to supply nutrients to the plants.

It might be best to take a moment and discuss some of the various hydroponic methodologies. The simplest involves just dripping a nutrient solution over the root area of a plant which is physically supported by an inert medium like pea gravel, perlite, or the like. The nutrient is then “discarded”, meaning it is not recirculated over the plant roots again. This isn’t a very efficient or cost-effective method, so it is rarely used.

Another simple technique is to create a bubbler system from plastic bucket-type containers. Stacking a 3.5 gallon bucket in a 5 gallon bucket is a popular design. The smaller bucket’s bottom is perforated and then placed inside the larger The space between the bottoms of the buckets serves as a nutrient reservoir. An aquarium air pump is used to power a tube system that “bubbles up” nutrient solution from the reservoir to the top of the planting media in the top bucket where it trickles down over the roots and, ultimately, drips back into the reservoir through the perforated bottom.

A different approach employs a method know as “ebb and flow”. In this method, plants are placed in an inert medium in small pots which are arranged in a large six-inch deep tray. Using a timer to control a pump in a reservoir below the tray, nutrient solution floods the tray– and the pots– for a specific interval, and then drains back to the reservoir. During this “ebb” time, the plant roots are kept moist by the growing medium, but are also exposed to increased amount of oxygen.

A system similar to ebb and flow, but simpler, is called deep flow. Pots remain submerged in nutrient solution, but the solution is oxygenated and recirculated constantly.

A more sophisticated system, called NFT– Nutrient Film Technique– employs the concepts of both feeding and supplying increased oxygen to the roots, but does them at the same time. Plants are situated in an inert medium in “net pots”, which are plastic pots with many small slots in their sides and bottom. The pots are inserted in the covers of plastic channels, known as gullies, through which a shallow film of nutrient solution flows. The slots in the pots allow roots to grow through the pots down into the nutrient film.

An offshoot of hydroponics is aeropononics. Also a soilless growing method, aeroponics goes one step further to almost eliminate the growing medium itself. In an aeroponic system, plants are suspended with their roots hanging in an opaque chamber. Nutrient is sprayed on the roots or misted in the chamber either constantly or at specific intervals.

My hybrid system employs elements of deep flow, NFT and aeroponics. Rather than have nutrient pumped in at one end of a gully to flow past roots on its way back to the reservoir, it is instead sprayed onto the net pots at each plant site. Additionally, the drain at the reservoir end of the gully is adjustable, allowing the depth of the film flowing down the bottom of the gully to be varied from very thin all the way up to nearly filling the gully. This adjustability allows seedlings placed in the system to start out under the deep flow technique, and, as their roots grow longer, the depth can be lowered allowing more oxygen to the roots in a hybrid aeroponic/NFT system.

This is not an original design. I found a commercially available system that very apparently uses mostly commonly available materials in its construction, so I decided to build one myself. After a few hiccups, I eventually got everything I needed and assembled the system. Some pics here.