My Kratky Hydroponics System

Introduction

I am writing this post to share with friends who are interested in setting up a minimal hydroponic system in no time at all. I have been able to grow many types of lettuce, kale, basil, Swiss chard, and arugula all year. It can comfortably grow 10 - 15 lettuce head full size per tray / 35 seedlings size in that same tray. Initially, when I built it in 2021, the entire cost was around $400 - $500. Given inflation, this price has increased somewhat, but it still beats a lot of the pre-made systems that are out there. I germinate seeds with this set up too.

My recommendation is to start out with just 1 light, 1 tray, and 1 type of lettuce to understand the flow and gain intuition for the system. Then, scale to 4 trays. I also started with one tray then scaled and refine for the entire system.

This is a Kratky style of hydroponic system. With this method, the roots of the plants are sitting in still (clean) water. Other methods are the Nutrient Filtration Technique (NFT) and the Deep Water Culture (DWC). The benefits of this system is that it is beginner's friendly. The light is the most advanced equipment. The photos can speak more to its effectiveness. Could it be better? Yes! Will I strive to optimize it further? Probably not intentionally. Hopefully, others reading this will try it out and help move this system forward.

However, the main disadvantage of this system is that it uses a lot of water. When the lettuce are in their mature phase, I need to refill about 2 to 3 gallons of water every 3 - 4 days. Then, there is the cleaning process. Once most of the lettuce heads are in maturity and harvested, I start over. Doing so has kept my system clean, and I never worry about root rot. Starting over means hosing the tray down with more water and soap. Low water usage is why NFT systems with water flow and irrigation are preferred over the Kratky method. Because this system can require a lot of water, I do not use it to grow really intensive plants such as tomato / squash / cucumber etc.

This is a low maintenance system until the lettuce reaches maturity phase. Then, it needs more attention in terms of replenishing the water tray/reservoir.

The entire process summarized

1. Germinate seeds under the light for 8 hours (2 - 3 days)
2. Move the seedlings to rockwool and place under the lights for 8 hours. These will eventually form true leaves. (2 weeks)
3. Move the true leaves seedlings to the hydroponic solution tray (pizza dough proofing box tray) that stay under the lights for 8 hours (4 weeks). The ppm of the nutrient should be around 1000 ppm to 1500 ppm.
4. Harvest and continue step 3
5. Clean up and repeat

Vegetables

The following are my favorite things to grow. Selecting just 1 packet is more than enough to last you a year. You can assume that any of these would be low maintenance. It does not matter which you choose but that you choose quality seeds.

• Burgundy Delights (Burpee). It has a beautiful, dark color and can grow very easily. Despite not having much room to grow or exposure to light when blocked by other plants, it manages to grow and thrive. My favorite by far. Produces soft leaves.
• Prizeleaf (Burpee). It behaves a lot like the Burgundy Delights. Also soft leaves. It does expand and can potentially block other plants. Just ensure you harvest the large leafs when this happens.
• Monte Carlo (Johnn's Selected Seeds). I learned about this one thanks to my friend and colleague, Jeff. I like that it can grow compactly and not require a lot of space. It's crunchy. I like to grow it in with Prizeleaf of Burgundy Delights because it adds texture variety.
• Black-Seeded Simpson (Burpee) - I started with these. I would state that they are my least favorite to grow because they're boring to eat and require more room. That said, still a good candidate to grow and easily available.
• Dark Red Lollo Rossa (Johnny's Selected Seeds) - Gorgeous colors, adds texture variety to your salad. They look sophisticated / high brow.
• Swiss Chard, Bright Lights (Burpee) - Beautiful color, tasty leafs that are comparable to spinach.
• Arugula, Garden Tangy (Burpee) . Arugula always enhances a boring salad bowl.
• Basil, Genovese (Burpee). My basil leaves look like they're on steroids. Great flavor and fragrant smell.
• Sage (Burpee) I grow it a month or two ahead for Thanksgiving. Goes great in stuffings.

Germinating seeds

My method is elementary with some tweaks to allow for all year germination. That said, this process took me a while to refine and delayed my progress in the beginning. It's why I am spending a lot of time in explaining this part.

I soak a paper towel, place some seeds onto the paper towel, use a spray to ensure that the seeds are coated in water. Then, I fold up the paper towel in fourths, place it in a zip lock bag.

I leave the zip lock bag directly under the Mars hydro light. This has ensured that I get seeds to germinate despite whatever season we're in. I longer put it into a dark closet or garage. Put it directly under the light for better germination rate!

By ensuring that I only transfer successful seedlings to the rock wool, I have eliminated a lot of rock wool waste.

I take out the seeds when they have barely cracked (about 2 days). This makes it easy to drop them into the rockwool. I try to avoid too long of germination because it is difficult to disentangle the seedlings and it helps avoid weak seedlings.

I run cold tap water over the rock wool then gently shake out the water excess. I take a chopstick and poke holes in the rock wool to make room for the seedlings. Place each seedling into the center of rockwool. Add about 1/2" of cold tap water into the container that hosts the rock wool.

Ensure that the bottom of the rockwool container is coated with at least 1/2" of water every day. Leave it under the Mars Hydro light for 8 hours a day. The seedlings are about 8" away from the lights. Avoid pouring water directly on top of the seedlings as it can drown them or cause "damping off". There is a wick effect in that the rock wool will pull the water up to the top.

To build

As the seeds germinate, there is not much to do but ensure that the tray is coated with 1/2" of water every day. With this in mind, you can start prepping the foam tray in preparation for the seedlings.

• Tray: Baker's Mark 18" x 26" x 3" White Heavy-Duty Polypropylene Dough Proofing Box - You can get these in the local restaurant supplies store or online. I got mine from a local store. I decided to use pizza proofing boxes because the dimension means it can hold 6 gallons of water. This is just the right amount. I've had containers that had too much height that it would require too much water. The longer that the roots sit in the water then the easier it is for root rot to occur. With this height, it allows me to replenish fresh water more frequently.
• Foam board: GreenGuard R- 5, 1-in x 2-ft Unfaced Foam Board Insulation
• Light: MARS HYDRO TS600 100Watt LED Grow Light 2x2ft Coverage I have been using these for a year without any problems or diminishing qualities. Sometimes, Mars Hydro has sales on Amazon that the price may fluctuate around $10 more or less.
• 1" hole saw: CRAFTSMAN 1-in Bi-Metal Arbored Hole Saw Using a 1" hole saw means that the 1" rockwool will be snug enough that you will not need the net cup at all.
• Shelf (optional): CRAFTSMAN Plastic Heavy Duty 5-Tier Utility Shelving Unit (40-in W x 24-in D x 72-in H) This shelf is amazing. It can hold up to 250 lbs per shelf. It's very light yet the design makes it very sturdy.

Drill the foam board with the 1" hole saw. Each tray should have 35 holes with 5 across and 7 down. This allows for starting maximum of 35 seedlings. Even though I can only grow 10 - 15 plants to full size, having a large number of seedlings in one tray allows me to start a new system for all 4 trays quickly and easily.

To grow

• Timer:DEWENWILS Mechanical timer DEWENWILS Mechanical Timer Power Strip with 8 Outlets, Flat Plug, 6ft Long Cord, Overload Protection, Indoor Timer. This is to run the lights in a cycle of 8 hours per day.
• Nutrients: MASTERBLEND 4-18-38 Complete Combo Kit Fertilizer Bulk (5 Pound Kit) These will last forever. You only need about 1/1/.5 tsp per tray. You can even buy the 2.5 lb package and it should last you at least an entire year. Also, much thanks to Jeff for introducing me to this one!
• Rockwool: 1" rockwool Conveniently, the rockwool fits the foam board holes perfectly I place them directly into the foam board without any net cups.
• TDS / pH meter: VIVOSUN pH and TDS Meter Combo I only use the TDS measure and not the pH meter. The tap water that I use has a pH level of 10, but it has not affected my grow quality much. If you follow the master blend ratio, I want to say that the TDS measurement is optional, but I think it is for the best that you should know the exact PPM of the water and nutrient to understand what is or is not working from the beginning.
• Net cup pots & clay pebbles (optional) JpGdn 50PCS 1.75" Mesh Net Cup Pots Basket Hydroponics System Supplies Aquaponics Seed Growing Media White & Clay Pebbles (optional) Hydroponics Clay Pebbles. These are great for blocking light to prevent algae from forming when you space out the seedlings. They go into empty baskets to cover the holes that do not have seedlings. That said, I have stripped aluminum foil or use other means to block light from reaching the water.

Below is a photo of the true leaves on the lettuce. When the seedlings begin to look like this, resembling what a mature lettuce would look like, is when I transfer it to the pizza box tray with the nutrients water.

The water nutrient is at 1000 ppm.

How I mix Masterblend

Conveniently, the pizza proofing box holds around 6 gallons of water that you can follow the recipe of 1/1/.5 tsp of Masterblend formula, calcium nitrate and epsom salt without using the TDS meter. That said, I like to start out with a concentrate then dilute it as I need it. This is convenient for the weeks when the plants mature.

I perused many Youtube videos and the math of these videos hurt my brain. So this is what I do: I use three containers for each nutrient. I take 1 tablespoon of calcium nitrate, 1 tablespoon of the Masterblend bag, .5 tablespoon of the epsom salt and place them into each individual container. I then pour hot water into each container (as much as it takes to dissolve). Then, I blend them together. I then use the TDS tool to dilute it with cold tap water to be about 1000 ppm for each individual tray.

Light conditions

• Keep the light around 12 inches away from the tray (standard paper size). I find that the Craftman shelf really allows for the perfect height distance and this has worked out well. I use zip ties to secure the lights.
• 8 hours per day from 9 am to 5pm. I find that I do not need that much light. There is also room for experimentation here.

Harvesting

There are two ways to harvest. The first is to pluck the entire lettuce head. I do this when there is not a lot of room, or when I feel that the lettuce is almost near the end of its life. However, in between, there are options for harvesting large leafs that just expand too far that they are blocking the light. I find that plucking these large leafs every Sunday can yield at least 1 x-large ziplock bag that makes for a good salad bowl.

Avoiding bitter taste of lettuce

Sometimes, I go overboard with the nutrients and par surpass the 1500 ppm which produces bitter tasting lettuce. No worries here! My mom, the would be engineer had she not grown up in warfare, figured out that placing lettuce leafs in cold salted water for at least 30 minutes produces really crispy and sweet lettuce leaves. Shake off excess water from lettuce, put into a ziplock bag. The lettuce should last for more than 1 month.

Timeline

This is the growing result from December 29, 2022 to February 11, 2023. Note that the growing time is slower in the winter than it is in the summer or fall. Still, it was a humble harvest, and I got to gift about 3 to 6 extra large ziplock bags to friends and family with 4 trays going at once.

December 29, 2022:

January 15, 2023

January 23, 2023

February 11, 2023

By mid February, the trays started to look like a grocery aisle. To be honest, I slacked off with this grow cycle because it was too cold and I was recovering from the holidays. I could have produced better results with watering more frequently. Still, the Burgundy Delights, Prizeleaf and Monte Carlo are so resilient.

Important: The positions of these plants are not static. I move them from time to time as I see them struggling with reaching the lights.

Avoid tip burn on leaves

Tip burn can occur in the later phase when there is rapid growth. To reduce this, I run a fan that is about 2 feet away from the lettuce. Instead of buying 4 set of individual fans, I use one large standing fan. I also stagger the grow so the fan will aim at the most mature phase while the young seedlings do not need fan.

Clean up

At the end of each tray's cycle, I hose down the tray and foam board, add some soap to the water, let it sit for a day. Then clean tray with a sponge.