WORDS: Brett McCormick, William McKenzie, and Alec Mayall

This hydroponic greenhouse is designed to feed four families with fresh produce throughout the year. With the collective financial investment and sweat equity of four different families, a shared greenhouse an easy way to connect with friends, family and/or neighbors and help the environment by cultivating your own food. Initial costs might seem high, but with a properly built structure and some TLC you will be able to cut your trips to the store down exponentially. Not only will you be saving money in the long run, you will know what you are consuming. In this issue we’ve chosen a 12’x24’ structure to demonstrate what type of facility would be needed to produce enough lettuce, bell peppers, tomatoes, and cucumbers for four families throughout the year.

(Click to see a larger image.)

Budget

There are many different types of greenhouse structure kits on the market today. You can find kits for greenhouses this size for around US$500. This would be a simple kit, only providing building materials for the actual structure. Other kits for this size of greenhouse range in the $2,000 to $4,000 range. These structures will provide you with a more aesthetically-pleasing greenhouse with better ventilation. Much of this budget is dependent on how technically inclined and handy you are. For practicality purposes, we will figure that the four families in this collective will complete all of the work, therefore minimizing the labor costs.

A conservative budget to get your hydroponic greenhouse fully up and running will be around $5,000 to $8,000. Many of these kits don’t supply a foundation, hydroponics systems, electricity, water, and many other factors that go into this budget. The further distance your greenhouse is from utilities (e.g. electricity, water), the more expensive it will be to run them to the greenhouse. When considering your budget and which features you’d like to include in your hydroponic greenhouse, remember that it is always easier to add internal features than it is to add size to your greenhouse.

Site Location & Preparation

When selecting a site it is important to ensure there is ample sun for the majority of the day. It is essential to have an open spot where the skies are clear to the east, west, and south. If you are unable to have completely clear skies facing these directions, you will reduce the maximum plant growth in your greenhouse. A little shade is acceptable, as this is a family-run project and you are not building a greenhouse for commercial production.

When considering the site for foundation preparation you should ensure that the site is level. As mentioned earlier, greenhouse kits don’t come with foundation kits, although most of them will tell you how to prepare a foundation. One simple solution is to use treated 4”x6” wood for your foundation. It is important that, while fastening these together, the foundation remains square and level. You can fasten these with decking screws or, even better, galvanized lags that will penetrate connecting wood to at least two inches. Anchoring your foundation is very important. To do this you can drill half-inch holes every 3 feet in the 4×6 and pound 24” rebar into the ground. You want to make sure that the rebar is flush to the wood so that they won’t get into the way of the actual greenhouse structure. Also, ensure that your foundation is slightly above grade.

Preparing the Floor

For your flooring, you want to use something that will drain easily but that is also easy to walk on. A simple option is gravel. Before you lay in the crushed rock, you want to ensure that you lay down black ground-cover fabric to ensure that all weeds are kept out of your ideal environment. It will actually benefit you if you lay this down before the foundation is set up, because otherwise the weeds will enter in through the corners of the foundation. The next steps are to secure the greenhouse to the foundation. From here you can follow the instructions of your greenhouse kit.

What’s for Dinner?

For this greenhouse, tomatoes, bell (sweet) peppers, cucumbers and lettuce are being grown.

Tomatoes

Tomatoes are started in 4” rockwool and are placed on rockwool slabs so the roots have more room to grow. The slabs are wrapped in plastic, so it is important to cut slits in the plastic to allow excess water to leak out. The slabs are placed directly onto the gravel so they can drain well. They are top fed from drippers. If you want more insulation under the rockwool slabs, you can put foam underneath so they aren’t touching the ground. This is not completely necessary, but it can help control the temperature of the root system. The rockwool slabs are 3’ long and can house 5-6 tomato plants. Each tomato plant will produce around 20lbs of fruit each season. You will need to train the young tomatoes to grow up onto a trellis system so that the plants can support the fruit. Rockwool is a good choice because tomatoes’ root systems can thrive in the small space and don’t need as much volume to be effective. As well, tomatoes are annual plants so you can spend the extra money for the rockwool as the rockwool will suffice for the entire season. Rockwool is a proven media for tomatoes and will promote vigorous growth. The tomatoes are planted in September and are pulled in July. This gives you time to clean out the greenhouse and start fresh for another year of crops.

Cucumbers

Cucumbers are started in 4” rockwool cubes and are grown in 5-gallon pots, two cucumbers per pot. Coir is the chosen medium for this because it is cheap, effective, and it is a byproduct, so we are preventing waste. Also, with coir you have the option to treat and re-use it for the next growing season. The cucumbers will need a trellis system to support them when they start to produce cucumbers. They are top fed through drippers from the main nutrient reservoir. In this greenhouse there are 20 cucumber plants: you can expect to produce 20-30 cucumbers per plant each season.

Peppers

Just like the cucumbers, the peppers are planted in 5-gallon pots, with coir as the grow media and a top-fed dripper system. You can expect to produce about 20 peppers per plant each season.

Lettuce

The lettuce is grown in a NFT system: it is the most effective technique for growing leafy greens, because lettuce has such a fast turnaround. The only media needed for this system is the media that you propagate your seeds in. You can either buy or make a NFT system. There are five 4”x4” troughs with 10 growing sites in each trough. The troughs should be placed about 4-10” apart, depending on the stage of growth that the lettuce is in. With this system, you should be able to crank out at least 10-15 heads per week or about 250 per season, depending on how you set it up and if you are constantly propagating and have a cycle going. In hotter months you can expect to cultivate your heads of lettuce in about 8 weeks, from seed to final product. It will take about 13 weeks in winter months. This will need a separate nutrient reservoir, which is constantly circulating. The troughs are set up on a slight slope so that they drain back into the reservoir. Make sure that you have the reservoir covered so that you don’t have a build up of algae.

Grow Environment

Ensure that you have vents on either side of the greenhouse for proper ventilation. Put screens around the vents to guarantee that no pests enter your greenhouse through these vents. Keep in mind that a very fine screen will inhibit proper airflow. One solution is to build a box wrapped in a fine screen so that there is more surface area for the air to pass through. Also, install multiple oscillating fans to ensure proper air movement.

The desired temperature is 65°F (18°C) at night and 75-80°F (24-27°C) during the day. The better quality polycarbonate product used will make heating and cooling easier.

If you have good air movement in your site, simple vents will suffice at moving air around your greenhouse and cooling it. The most consistent way to cool your greenhouse is with an electrical fan, pulling in cold air and pushing out the hot air. Another economical way to cool your greenhouse is to have an evaporative cooling system. This works very well in areas of low humidity and high temperatures. For areas with higher humidity and lower temperatures, it isn’t as effective. An evaporative cooler will be able to lower temperatures by 5-7°F (14-15°C). A last resort to cooling is using shades. They are are sold in different colors and densities, but the white fabric is the most effective cooling shade for the light that it cuts out. Usually they are applied in the spring and are taken off in the fall when the temperatures start to drop.

Good Green Builders was founded in December of 2009. It’s a first-of-its-kind general contracting company that specializes in the construction of indoor hydroponic grow rooms. Based in the San Francisco Bay area, GGB offers a complete line of services and equipment to accommodate the needs of anyone who desires to have an indoor garden.

How many people can you feed with your indoor garden? Share your tips, tricks and lessons-learned below!

Keith’s first prototype raft system made from a plastic tote. Plants shown were grown under a 95W 6500K fluorescent bulb which is said to provide similar output to HID systems yet without as much heat. Not bad for three week old lettuce.

Beat the winter blues this year by creating your very own salad factory that can run 365 days a year! Keith Roberto, author of “How To Hydroponics,” takes us through the process step-by-step.

There are many ways to grow lettuce hydroponically. Here’s a system that’s simple, inexpensive ($20-$30 complete) and “complex” enough to satisfy any first timer’s appetite for a fun project that actually works pretty well. It’s called the “Raft System.” In concept, the raft system does exactly as it says. Plants are grown in Styrofoam “rafts” that float in a shallow pool of nutrient solution. To keep the nutrient from stagnating, a small air pump is used to deliver oxygen to the solution and the eagerly awaiting roots.

Parts List

(1) 14 Gallon Roughtote reservoir
(1) Single outlet air pump (Elite 801)
(1) 2’ x 2’ x 1.5” rigid foam sheet
(9) 2” net cups
(1) 6’ x 1/4” air tubing
(1) Air stone
(1) Small bag of LECA
(9) Seed starting/rooting plugs
(1) 1/4” compression grommet
+ Hydroponic nutrients

Tools You’ll Need

Electric or battery powered drill
3/8” or 1/2” chuck 1 7/8” hole saws for cutting plant sites
3/8”drill bit for drilling grommet hole
Jigsaw or coping saw for cutting foam
Razor knife for cutting tubing
A pen or marker

Step 1: Trace the outline of your container onto the styrofoam sheet.

Step 2: Measure the distance between the outer edge of your container and the inner wall (measurement ‘X’).

Step 3: Be sure to cut the styrofoam ‘X’ inches smaller than your outline so that it fits neatly inside the container. After a little bit of additional trimming, you should have a perfect fitting “raft” as shown on the left. Make sure the styrofoam raft can move freely up and down inside the reservoir with it full of water since the pressure may deform it a bit. If this is the case, simply trim away until you can get 4-8” of up and down movement. This is very important for this system to work properly.

Step 4: Layout the grow sites on your styrofoam raft and use a hole saw to cut them out. If you don’t have access to a hole saw, you may be able to use a utility razor to perform the same task albeit more challenging!

Step 5: Mark off the lowest point your raft will reach inside the container (due to the wall taper or internal obstruction) so that you’ll know when to top it off in order to prevent the nutrient level from dropping away from the bottom of the raft and leaving your plants high and dry.

Step 6: Drill a 3/8” hole in the bottom wall of your container and insert the 1/4” rubber compression grommet. Pass your air tubing through the grommet and attach to your air stone. REMEMBER! You must mount your air pump higher than the maximum water level in your container to prevent back flow of nutrient solution through the air tubing and into the pump.

Step 7: Time to plant your favorite seeds! I used scissors to trim the bottoms off the Perfect Start #2s since they were just a bit too long for the little 2” cups I used here.

Use LECA stones to back fill around the seeded plugs and place them into each of the grow sites in your raft.

Step 8: Fill ‘er up! Add water, nutrients and plug in your pump: your raft garden will start gurgling and your plants will grow in no time – don’t forget to give them plenty of light and top off the nutrient solution every time it drops 2-4” or so. It’s also a good idea to completely flush and clean your raft system every other harvest using a 10% bleach solution and scrub brush.

The Perfect Environment For Lettuce

Temperature: Lettuce prefers cooler temperatures. It bolts rapidly if things get too hot, especially if temps exceed 80 to 85°F (27 to 29°C). Ideal temps for most commonly grown varieties: 64 to 70°F (18 – 21°C) during the day and 55 to 61°F (13 to 16°C) at night. Higher temperatures can also cause burning on the leaf tips.

Relative Humidity (RH): 60 to 80 percent.

Nutrient Solution pH: 5.5 and 5.8 and EC from 0.6 to 1.0

Lighting: Compact fluorescents are ideal for the production of salad greens indoors. Lights should be switched on for 14-18 hours per day. Increasing nitrogen levels if growing under longer day lengths will speed up growth significantly.

Eager for more DIY hydro-projects? Check out Keith’s website, and stay tuned for more weekend projects from Urban Garden Magazine!