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!