Module 4: Materials and Setup

Level: 🟢 Beginner
Prerequisites: Modules 1-3
Estimated time: 30-40 minutes (reading) + 20 minutes (assembly)
Goal: Gather materials and assemble your first Kratky hydroponic system.

What You'll Learn

By the end of this module you will have a complete parts list, know where to source each item, understand container selection criteria, and have step-by-step instructions to build your Kratky system.

4.1 Complete Parts List

Here's everything you need. You can find all of these items at local garden centers, hardware stores, or online.

Container System

Nutrients and Testing

Seeds and Lighting

Tools (likely already have)

• Drill with 3-inch hole saw OR sharp craft knife
• Measuring cup or kitchen scale
• Permanent marker

Total cost (first build): $22-30 without optional items
Total cost (with pH kit and grow light): $50-80

4.2 Container Selection Criteria

The container is the foundation of your system. Choose carefully.

Must-Have Features

Opaque (light-blocking):
Algae grows in light. If light reaches your nutrient solution, you'll have a green, slimy mess within days. The container must block all light.

Test: Put the container over a flashlight in a dark room. If you see light leaking through, it won't work.

Food-safe material:
Look for HDPE (high-density polyethylene) plastic, marked with recycling code #2. This is the same material used for food storage and won't leach chemicals into your water.

Avoid containers that previously held non-food chemicals (paint, motor oil, cleaning products).

2-5 gallon capacity:

• 2 gallons: Minimum for one lettuce plant. Requires more frequent top-offs.
• 3.5 gallons: Ideal for one plant. Good balance of size and water reserve.
• 5 gallons: Works great, provides the longest water reserve between refills.

Larger is better for beginners because pH and nutrient concentration change more slowly in larger volumes.

Wide opening:
The lid must be wide enough to cut a hole for a 3-inch net pot. Most 5-gallon buckets have 10-12 inch diameter lids, which is perfect.

Good Container Options

5-gallon bucket with lid ($5-10)
The classic choice. Food-grade buckets are sold at hardware stores. Restaurants often give away used pickle or frosting buckets (wash thoroughly).

Storage tote (opaque) ($8-12)
Sterilite or Rubbermaid storage containers work if they're opaque. Bonus: flat lids are easier to cut than curved bucket lids.

Repurposed containers (Free)
Large yogurt containers, ice cream tubs, or protein powder jugs work if they're opaque and food-safe. Just make sure the lid is secure.

Containers to Avoid

• Clear or translucent plastic: Light leaks will grow algae
• Glass jars: Too transparent, and algae grows on glass easily
• Metal containers: Can react with nutrient solutions, especially at low pH

4.3 Growing Medium Options

The growing medium anchors the plant in the net pot and wicks moisture to young roots. It doesn't provide nutrients (that's the water's job).

Clay Pellets (Hydroton / LECA)

Description: Expanded clay balls, lightweight, porous, inert.

Pros:

• Reusable (wash and sterilize between grows)
• Excellent drainage and aeration
• pH neutral
• Lasts for years

Cons:

• Dusty straight from the bag (rinse before use)
• Can be expensive for first-time purchase

Best for: Long-term hydroponic growing, multiple crops

Cost: $10-15 for a 10-liter bag (supports dozens of plants)

Coco Coir

Description: Shredded coconut husk fiber, looks like soil but is inert.

Pros:

• Retains moisture well (good for seedlings)
• Biodegradable (compost after harvest)
• Cheaper than clay pellets
• pH neutral

Cons:

• Single-use (degrades over time)
• Can be dusty (rinse before use)

Best for: Beginners, those who prefer natural materials

Cost: $8-12 for a compressed brick (expands to 2 gallons when hydrated)

Rockwool Cubes

Description: Spun volcanic rock and basalt, comes in pre-formed cubes.

Pros:

• Excellent for seed starting
• Holds moisture and air perfectly
• Sterile out of the package

Cons:

• Rockwool cubes are alkaline out of the package (pH 7.5-8.0). This high pH locks out iron and other micronutrients, stunting seedlings. Pre-soak cubes in pH 5.5 water for 24 hours before planting to bring them into the optimal range.
• Not reusable
• Can irritate skin (wear gloves when handling dry cubes)

Best for: Starting seeds, then transplanting the cube + seedling directly into clay pellets or coco

Cost: $10-15 for a sheet of 50 cubes

Recommendation for Beginners

Start with coco coir if you want simplicity and lower cost. Upgrade to clay pellets after your first successful grow if you plan to continue. Use rockwool cubes for seed starting regardless of which medium you choose for the net pot.

4.4 Nutrient Selection

Your first bottle of nutrients will last 20+ grows, so choose wisely.

Recommended Options

General Hydroponics Flora Series (3-part) ($30-40 for the set)
The gold standard. Three bottles (FloraGro, FloraMicro, FloraBloom) let you adjust the formula for growth stage. Excellent for learning. Downside: more measuring required.

General Hydroponics MaxiGro (powder) ($15 for 2.2 lb)
Single powder, just add water. High nitrogen formula perfect for lettuce and leafy greens. Very economical. Downside: only good for vegetative growth (not fruiting plants).

Masterblend 4-18-38 + Calcium Nitrate + Epsom Salt ($25-30 for all three)
The most economical option, popular with commercial growers. Requires mixing three separate components every time. Best for experienced growers or those planning to grow at scale.

Fox Farm Hydro Formula ($15-20 per bottle)
Organic-based hydroponic nutrients. Slightly more expensive but high quality. Good for beginners who want a single-bottle solution.

For Your First Grow

Buy a single-bottle all-in-one like MaxiGro or Fox Farm. Avoid 3-part formulas until you're comfortable with the basics. The simpler the mixing process, the less room for error.

Look for "complete" or "all-in-one" on the label. This guarantees it includes all macro and micronutrients.

4.5 Seed Starting Basics

You can't transplant soil-grown seedlings into hydroponics (soil harbors bacteria and clogs systems). You need to start seeds in a hydroponic-compatible method.

Method 1: Rockwool Cube (Recommended)

1. Soak rockwool cubes in pH 5.5 water for 24 hours
2. Place 2-3 seeds on top of each cube, press lightly
3. Put cubes in a shallow tray, keep moist but not waterlogged
4. Cover with a humidity dome or plastic wrap until seeds germinate (3-7 days)
5. Remove cover once sprouts appear
6. Transplant the cube + seedling into the net pot once true leaves appear (10-14 days)

Method 2: Paper Towel Method

1. Moisten a paper towel, fold it over the seeds
2. Place in a sealed plastic bag in a warm location (70-75°F)
3. Check daily, transplant to a growing medium once the root emerges (3-5 days)
4. Gently place the sprouted seed in coco coir or clay pellets in the net pot

Method 3: Direct Seed in Growing Medium

1. Fill net pot with coco coir or clay pellets, pre-moistened
2. Make a small depression, place 2-3 seeds
3. Cover lightly with medium
4. Keep moist by misting or bottom-watering until seedlings emerge
5. Thin to one seedling once they have 2-3 sets of true leaves

Germination time for lettuce: 3-7 days at 65-75°F

4.6 Assembly Instructions

Now let's build your Kratky system. This takes about 20 minutes.

Step 1: Clean the Container

1. Wash the container and lid with dish soap and hot water
2. Rinse thoroughly (soap residue can harm plants)
3. Optional: sanitize with a 10% bleach solution, rinse very well
4. Dry completely

Step 2: Cut the Hole in the Lid

Option A: Drill with hole saw (cleaner result)

1. Mark the center of the lid with a permanent marker
2. Attach a 3-inch hole saw to your drill
3. Drill slowly, applying steady pressure
4. Clean up any rough edges with sandpaper

Option B: Craft knife (no drill needed)

1. Trace the bottom of the net pot on the lid with marker
2. Cut inside the traced line using a sharp craft knife
3. Cut small sections, work slowly (plastic can crack if rushed)
4. Test-fit the net pot, trim as needed until it sits snugly

The net pot should rest on the lip of the hole, suspended in the container. It should not fall through or wobble excessively.

Step 3: Prepare the Growing Medium

For clay pellets:

1. Rinse pellets in a colander under running water (removes dust)
2. Continue rinsing until the water runs clear
3. Let drain

For coco coir:

1. Break off a chunk of the compressed brick
2. Place in a bucket, add water (it expands 5-7x in volume)
3. Let soak for 15 minutes, fluff with your hands
4. Rinse thoroughly until runoff is clear to remove salt residues from coastal processing, or purchase pre-buffered coco coir
5. Squeeze out excess water (should be moist, not soaking wet)

Step 4: Assemble the Net Pot

1. Fill the net pot about 1/3 full with your growing medium
2. If you have a seedling in a rockwool cube, place it in the center
3. Fill around and over the cube with more growing medium
4. The medium should come to about 1/2 inch below the rim of the net pot

If you're starting seeds directly, follow Method 3 from section 4.5.

Step 5: Mix the Nutrient Solution

1. Fill the container with water (tap water is fine for most locations)
2. Leave 2-3 inches of space at the top
3. Measure your water volume (important for accurate nutrient dosing)
4. Add nutrients according to the bottle instructions (usually 1-2 teaspoons per gallon)
5. Stir thoroughly with a long spoon or stick
6. Optional: Test pH (should be 5.5-6.5, adjust if needed)

Step 6: Final Assembly

1. Place the net pot into the hole in the lid
2. Lower the lid onto the container
3. The bottom of the net pot should touch the water surface
4. The water should wick up into the growing medium, keeping it moist
5. As the seedling grows and drinks, the water level will drop naturally

4.7 Placement and Lighting

Natural Light

Place your system in a location with:

• 6-8 hours of direct sunlight per day (south-facing window in Northern Hemisphere)
• Temperature: 60-75°F is ideal for lettuce
• Airflow: Don't seal in a closet; room air circulation is sufficient

Grow Light Setup

If using a grow light:

1. Hang the light 12-18 inches above the net pot
2. Plug the light into a timer (12-16 hours on, 8-12 hours off)
3. Adjust height as the plant grows (maintain 12-18 inch distance)

4.8 What's Next

Your system is now built and ready. In Module 5, you'll learn how to transplant seedlings, monitor water levels, test and adjust pH, and maintain your system through harvest.

Next Steps

Previous: Module 3: Choosing Your First System
Continue to: Module 5: Planting and Maintenance

Course Overview:
01. Introduction to Hydroponics
02. Understanding Plant Nutrition
03. Choosing Your First System
04. Materials and Setup (you are here)
05. Planting and Maintenance
06. Troubleshooting and Next Steps