Deep water culture (the hydroponic lettuce raft system) is probably the simplest and most economical hydroponics system you could build. Although very simple to set up and operate, it is actually superior for growing lightweight, leafy vegetables like lettuce, herbs, and small peppers. They grow like wildfire in this system.
Hydroponic Lettuce Raft System
A lettuce raft makes an impressive, “futuristic” display and is a favorite with school teachers and for science fair projects (use an aquarium for the reservoir so you can see the roots).
We always have the lettuce raft bubbling away in the grow room no matter which other projects we are currently growing.
Nothing like steak and fresh lettuce salad!
Here’s how the deep water system works
Plants are grown in tiny net pots that sit in a styrofoam raft. The raft floats on a shallow pan of nutrient solution, which acts as the reservoir. The roots grow right through the net pots and into the solution pan. A small air pump and bubbler keeps the nutrient solution well aerated and delivers oxygen to the roots of the plants.
A fun, easy-care, and prolific system!
Think Big! Learn to build a large Lettuce Raft System [2X4 raft for 20 plants!] Read all about it here: Simon’s Simple Hydroponic Plans.
Not ready for a large garden yet? Get started below with our small raft lettuce mini-farm [6 plants] free plans!
How to build a small lettuce raft system
This is a “lettuce growing machine”! If you start some new seeds every 30 days and replace each head of lettuce as you harvest with a new baby seedling, you can have a perpetual supply of crisp, healthy salad greens.
The setup we provide here can grow six heads of lettuce at a time, and the whole unit costs less than $50 (not including a lamp and food).
Most of the materials are available from Home Depot or Walmart. A few items must come from a hydroponics supplier (but we give you a good cheap
Deep water system supply list
- Shallow reservoir pan (Sterilite 34 qt Latch Box tote works well) this bin is about 23½ X 14½ X 6” deep on the inside [Walmart]
- Can of cheap flat black spray paint [Walmart]
- Aquarium air pump, 6 feet of airline tubing, “T” connector & 5” airstone [Walmart]
- Rigid styrofoam sheet, 1-1/2 to 2” thick; cut a piece to fit inside the reservoir pan. You can buy a 4X8 foot sheet at Home Depot for about
$20. It seems a shame to buy a huge sheet of it for one little piece, but you can always save it for use later when you are ready to build
your big 2X4 foot lettuce raft! An alternative is to cut a slab from an old styrofoam ice chest of the right thickness.
- 6- 2” net cups: Cheap Hydro Supplies
- Small bag of LECA (Hydroton or clay balls), [hydroponics supply, eBay or Amazon]
- Styrofoam building insulation, 2” thick air pump kit
Tools needed for building a lettuce raft
- Power drill
- 1-3/4” or 1-7/8” hole saw & a 2” hole saw (Borrow a hole saw kit or buy one, you will definitely use it again).
- Jigsaw, coping saw, or table saw to cut the styrofoam
Getting the styrofoam ready for the raft
1. First cut the styrofoam raft to fit inside the reservoir bin: use a jigsaw, cutoff saw, table saw, or even a handsaw. The piece needs to be just a tad smaller than the inside of the bin so it will easily ride up and down a couple of inches without binding (when the water level drops).
This is important for the raft to work right.
But, you do want it to cover the top of the water as tight as possible. In our case, for this Sterilite bin, we cut the styro piece 14-1/4” X 23”.
TIP: Cut the styrofoam outside in the yard, preferably when it’s snowing. You can thank me for this little tip right now…
Store the rest of the sheet of Styrofoam. You can use more of it when you’re ready to upgrade to a full-sized lettuce raft. Also, you’ll find many other uses for the leftovers: we did.
2. You will likely need to round off the corners so the raft will ride up and down freely in the bin. Take care with your block of styrofoam, treat gently, as it is easy to bust it.
3. Mark off the styrofoam block for six holes, evenly spaced, so that there are six inches between each hole, both ways. It doesn’t matter if plants ride over the sides of the bin a little, just so they don’t crowd each other. So for our 14 ¼ X 23” block, this is how we centered the holes:
4. Now cut the pot holes in the styrofoam block. Start with the 2” hole saw first. From the UP side of the raft, cut a shallow 2” hole, centered over the marked center holes. Cut all 6 holes just to a depth of about 1/4”, then switch to the 1 7/8” hole saw to finish up. (Our set did not have 1 7/8” so we used 1 3/4”).
Using the center hole as a guide, now cut down as deep as the hole saw will let you go. Do all six from the UP side of the raft. Then use a nail to go down thru the center holes and pierce the backside of each hole. This is so you will know where to drill next from the backside. Then cut with the same size hole saw from the backside of the styrofoam block all the way flush.
5. Then carefully pull out the cut plugs and clean up the holes a little. Try out the net pots. You want them to sit in nicely and bottom out at the bottom of the styrofoam, but not fall through.
Seting up your raft
6. Next, spray paint the outside only of the clear reservoir bin, to make it light proof. Spray several coats and use the entire can. Do not spray the inside of the bin.
This light-proofs the system and prevents algae from growing.
Just about ready to load this baby up!
Important: Place the air pump higher than the reservoir to prevent nutrients from backing up into it.
7. Set up the tray on sturdy level support, (its final resting place). Fill with 6 gallons of water. Place the airstone in the bottom of the tray, connect to the air pump, and plug it in to test it.
8. Next, add your favorite nutrient solution to the vat. If you are using GH Flora Series (recommended), add 6 tsp. each of the Flora Grow, Flora Micro & Flora Bloom, (one at a time, in that order). Adjust the pH with a test kit (more on this and ordering info in the Tips ‘N Techniques section below).
9. Next, float the styrofoam raft on top of the nutrient solution. You want it to ride at the very top, so add more solution if your bin requires more than the 6 gallons.
Raft hydroponics is tailor-made for growing lettuce. The deepwater culture provides a perfect growing environment for lettuces, herbs, and small peppers. However, lettuce is by far the most popular crop grown on these units; hence, the name “lettuce raft”.
Lettuce is widely grown commercially in hydroponic greenhouses and supplies a growing market demand as a gourmet, high-quality food.
Most hydroponic lettuce is the Bibb or Buttercrunch varieties, which form a soft fluffy head, not like the dense compact iceberg lettuce. You might try also some specialty lettuces to add variety to your salad bowl. Romaine, Oakleaf, and Ruby are popular.
Planting the seedlings
10. Time to transplant your baby seedlings into the raft. Place the starter plugs into the net pots and carefully pack around them with LECA (clay balls) to help support each plant in its pot. Push the little net pots into the pre-cut holes in the styrofoam raft.
11. Plug in the airstone bubbler and watch ’em grow!
We had been harvesting the outer and lower leaves of these Romaine lettuces for salads. We went out of town for the weekend, turned the thermostat up, and forgot to leave a fan on; the poor darlings bolted! (No, they didn’t take off, just went past their prime ’cause it got too hot).
Above you can see how the leaves are drooping out instead of nice and tight. We harvested the whole raft after we took this picture and had an enormous Caesar salad. Yum!
This is a photo of a different type of lettuce from our large raft. Just wanted you to see what happens to the roots. They grow down into the solution reservoir.
Our favorite lettuce to grow in the deep water system
Don’t forget that lettuce grown outside is a cool-weather crop. Indoors in your hydroponics set up, try to keep the temperatures below 75°. For a continual harvest and the most effective use of your lettuce raft, plan ahead so that each head of lettuce you harvest can be replaced with a new seedling ready to go.
These are some of our favorite varieties:
Loose-leaf (also called cutting lettuce) – fast-growing and do not form tight heads. These are the lettuces you see in the market of various different colors, bronzes, and reds. They create the most attractive and tasty salad bowl. Check seed packets to find a variety of colors.
Oak Leaf lettuce – also is a quick grower and can tolerate warmer temperatures. Puts out delicious tender oak-shaped dark green leaves.
Bibb – a small-headed variety with a delicious sweet taste. One head of Bibb makes for a good salad. More heat and disease resistant than others.
Buttercrunch – a classic favorite, produces heads with a luscious, buttery texture. Also heat resistant.
Romaine – Caesar salad anyone? Romaine lettuce produces elongated thick crisp and savory leaves. Romaine is probably the most heat-resistant lettuce you can grow.
Lettuce raft tips & techniques
You can use just the light from a sunny window if all you are growing are herbs. Anything else requires some supplemental lighting. A T5 compact
fluorescent “grow light” will do fine for houseplants, herbs, and leafy green veggies like lettuce.
TIP: the grow room must be kept cool for lettuce. Use a fan on low in there to cool it down.
You can get off much cheaper by getting a fluorescent “grow stick” at Walmart for about $25, but you will not get the lush growth a better light setup will produce. Also, for best results, upgrade to a 200-watt bulb.
Learn more about hydroponics lighting here: Hydroponic Lights.
We highly recommend the Flora Series nutrient solutions put out by GH (General Hydroponics). This stuff is superior, easy to use, and reasonably priced. It consists of 3 parts (Flora Grow; Flora Micro; and Flora Bloom). If you have hard water, get the Hardwater Flora Micro instead.
For this lettuce garden, order a quart of each of the three solutions. Stick with Flora Series, follow the label directions, and you can’t go wrong!
The nutrient solution must be kept cool (55-70°). This is especially important for cool-season crops like lettuce. Learn more about hydroponics nutrient solutions here: hydroponics solution. We also provide a nifty little mixing chart for the Flora nutrients you can print out and save.
As the nutrient level drops in the reservoir bin, you need to periodically add water only (not more nutrient). Keep track of how many gallons you top up with. When you have replaced a total of 3 gallons of water, stop topping up and let the level drop down quite a bit. Then drain the bin and mix up a whole new batch of nutrient solution.
Each new 6-gallon batch should last 4-5 weeks or a whole growing cycle for a crop of lettuce.
It is a very good idea for any serious hydroponics project to keep the pH of the water in the proper range, which is 5.5 to 6.5 (6.0 is ideal). If the pH is out of range, some of the nutrients get “locked out” and the plants suffer.
GH puts out a simple test kit with pH up & down solutions cheap. It will last you through many gardens.
The growing medium for a lettuce raft is actually the grow sponge or cube the seedlings started in. Then the Hydroton balls are jammed in around the seedlings to help support them in the little net pots. Large pots are not needed because the roots quickly outgrow the pots and extend down into the solution.
Hydroton balls must be ordered from a hydroponics supplier. But for the tiny bit needed for this small raft, try eBay for a small bag of it. Heck, for that matter, you could just jam little bits of Styrofoam between the grow sponge and the sides of the net pot. Just don’t use anything that would alter the nutrient solution, like stones or wood.
Learn more about hydroponic growing media here: Hydroponic Growing Medium.
Hydroponic lettuce raft system final thoughts
We hope you will try out our plans for this cool little lettuce raft system. You will be amazed at the quantity of produce you can reap from this unit. It provides a great introduction to hydroponics for adults and children alike, and it’s just plain FUN.
The lettuce raft makes a classic science fair project. Use a 10-gallon fish tank instead of the black tray we use here. Cover the glass sides of the tank by taping thick paper or cardboard to block out the light (this prevents algae). Then remove the paper covering when you are ready to display the lovely roots for all to see!
Our guess is that once you get a taste of hydro in this way, you will go on to bigger and better things. This field of horticulture is wide open! There are many different methods for you to try, and you’ll just get more knowledgeable and skilled at it as time goes on.
You might try growing heirloom tomatoes, medical herbs, or even orchids. Or you might just enjoy munching on your own healthy, homegrown salad
No matter which way your interests take you, you are sure to enjoy this clean, healthy, prolific, earth-friendly gardening method. We just love hydroponics and know you will too.
Explore our website often for updates on equipment, lighting, nutrition, plants and seeds, pests, grow-closets, and plans for several other different growing systems.
We provide simple information, insider secrets, and easy-to-follow instructions to get you up and growing in no time…