I am a longtime gardener, but I have never used rockwool, grown in a DWC, or used a floating raft. So I set out to do all three. I got one sheet of Grodan 1.5 x 1.5 grow plugs, one 2 x 2 flood tray by Brotherhood products, and the KonTiki lettuce raft, also by Brotherhood products.
The raft is designed to float inside the flood tray. It has 16 3.75-inch holes, each holding a 3.75 net cup. I also used a 4-outlet, 12-watt air pump to aerate the water and a Bluelab Truncheon Nutrient Meter. The pH must be measured, and it’s always a good idea to know your EC or PPM. But this can be done with less expensive equipment.
Next, I got started with the rockwool cubes. Rockwool is one of the more popular hydroponic growing media, as they are great ways to support plants and are fairly easy to use. I soaked my rockwool cubes in a pH solution of 5.5. I let it sit for the afternoon, drained off excess water, and placed a few seeds in each hole, pushing a little of the rockwool into the hole so the seed would be in the dark. Five days later, this is what I had:
The next step is to take each little cube and plant one in each net cup. There are a few types of growing media you might use here, but the product I chose is called Growstone GS-1 Hydro Stones. I rinsed the stones with fresh, non-chlorinated water and placed some stones on the bottom of the cup. Then, I put the cube in the center and added enough stones to surround and hold the cube in place.
While the rockwool was soaking, I filled the flood tray with seven gallons of non-chlorinated water. Then I added 60 ml of General Organic Bio Thrive Grow and two teaspoons of CaMa+, and adjusted the pH to 5.5.
I threaded an air hose through each corner of the net cup and planted those first. I proceed to plant the net cups in place. I used two 2-ft lamp fixtures running 6500K tubes using 192 watts of power providing 350 par watts (Photosynthetically active radiation).
Lettuce has a light saturation point of 420 par watts, so I used enough light to nurture the plants without stressing them. Within one month of getting the plants into their new growing media, I had 16 heads of sweet, fresh lettuce.