Module 5: Planting and Maintenance

Level: 🟢 Beginner
Prerequisites: Modules 1-4
Estimated time: 25-30 minutes
Goal: Learn to transplant, monitor, and maintain your Kratky system from seedling to harvest.

What You'll Learn

By the end of this module you will know how to transplant seedlings into your system, understand the air gap principle, monitor and adjust pH, top off or change water, recognize harvest readiness, and clean your system between grows.

5.1 Transplanting Seedlings

Your seedling is ready to transplant when it has 2-4 true leaves (the leaves that appear after the initial seed leaves). This usually happens 10-14 days after germination.

What You Need

• Your assembled Kratky system (from Module 4)
• Seedling in rockwool cube or growing medium
• Additional growing medium to fill around the seedling

Transplant Steps

Step 1: Verify the seedling is ready

• Seedling has 2-4 true leaves
• Stem is sturdy (not leggy or floppy)
• Roots are visible at the bottom of the rockwool cube or growing medium

Step 2: Prepare the net pot

• Fill the net pot 1/3 full with your chosen growing medium (clay pellets or coco coir)
• Create a small depression in the center

Step 3: Position the seedling

• Gently place the rockwool cube (with seedling) into the depression
• The top of the cube should be level with or slightly below the rim of the net pot
• Support the seedling so it stands upright

Step 4: Fill and secure

• Add more growing medium around and over the rockwool cube
• Fill to about 1/2 inch below the net pot rim
• Press gently to secure the seedling (don't compact too hard)

Step 5: Place in the system

• Set the net pot into the hole in your Kratky container lid
• Check that the bottom of the net pot is touching the water surface
• The growing medium should be wicking moisture from the water

Step 6: Label and date

• Write the plant variety and transplant date on the container with a permanent marker
• This helps you track growth and predict harvest time

Transplant Shock Prevention

Seedlings may wilt slightly after transplanting. This is normal. Minimize shock by:

• Transplanting in the evening or on a cloudy day (less stress from intense light)
• Keeping the seedling well-hydrated before and after transplanting
• Avoiding damage to roots during the process

Most seedlings recover within 24-48 hours and resume growth.

5.2 The Air Gap Principle

The Kratky method works because of a simple but clever principle: as the plant drinks water, the water level drops, and roots that were submerged are exposed to air. These become air roots (oxygenated roots), while new roots grow down into the remaining water.

How It Works

Week 1-2 (Seedling stage):

• Water level is high, touching or nearly touching the bottom of the net pot
• Young roots have low oxygen demand
• The plant establishes root mass

Week 3-4 (Growth stage):

• Water level has dropped 2-4 inches
• Top roots are exposed to air, becoming air roots
• New roots grow downward into the nutrient solution
• The plant has both water roots and air roots

Week 5-6 (Mature stage):

• Water level has dropped significantly (possibly 6-8 inches)
• Most roots are air roots, only root tips are in water
• The plant's oxygen needs are fully met
• Ready for harvest

The Critical Rule

Never raise the water level above the lowest air roots once they form (usually week 3+).

Exception: In weeks 1-2, before significant air roots develop, you CAN top off to the original level if hot weather causes rapid evaporation. After week 2, never raise above the lowest air roots.

If you top off the water in weeks 3+, you re-submerge the air roots. Air roots cannot function underwater (they lack the structures for submerged respiration). Re-submerging them can cause root rot.

If the water level is very low and you're concerned:

• Top off with nutrient solution to within 2-3 inches of the current level
• Never raise it higher than the lowest air roots
• Better to let the plant finish its growth cycle and harvest on time

5.3 pH Testing and Adjustment

pH naturally drifts over time. In a Kratky system, pH tends to rise as the plant grows. Check pH weekly.

When to Test

• Day 1 (after mixing nutrients): Establish your baseline
• Day 7: First check, usually pH hasn't drifted much yet
• Day 14 and onward: Check weekly, adjust as needed

How to Test (Liquid Drop Kit)

1. Draw a small water sample from your container into the test vial
2. Add the specified number of pH indicator drops (usually 3-5 drops)
3. Cap the vial, shake gently to mix
4. Compare the color to the chart provided with the kit
5. Read the pH value (should be between 5.5 and 6.5)

When to Adjust

pH is within 5.5-6.5: No action needed. Your plants are happy.

pH is above 6.5 (too alkaline):

• Add pH down solution (usually phosphoric acid)
• Start with 1-2 ml per gallon, stir, wait 15 minutes, retest
• Repeat if needed

pH is below 5.5 (too acidic):

• Add pH up solution (usually potassium hydroxide)
• Start with 1-2 ml per gallon, stir, wait 15 minutes, retest
• Repeat if needed

pH Drift Is Normal

Don't panic if pH drifts to 6.8 or drops to 5.2 temporarily. Plants are resilient. Adjust gradually over 24 hours rather than trying to fix it immediately.

Lettuce tolerates a pH range of 5.5-7.0, but growth is fastest in the 6.0-6.5 sweet spot.

5.4 Water and Nutrient Management

Water Top-Off vs. Full Change

Water top-off (weeks 1-4):
If the water level drops more than 50%, you can add water or weak nutrient solution (half-strength) to prevent the reservoir from running dry too early.

Rules for top-off:

• Don't raise the water above the lowest air roots
• Use plain water or half-strength nutrients (half-strength = 50% of label recommendation; e.g., if label says 2 tsp/gal, use 1 tsp/gal for top-off)
• Top off only once mid-cycle, if needed

Full reservoir change (not usually needed):
In a Kratky system, you typically don't change the water. The plant consumes nutrients and water at roughly the same rate, so the concentration stays stable.

Change the reservoir only if:

• You suspect nutrient imbalance (rare in a 4-6 week lettuce grow)
• pH won't stabilize after adjustments
• Water smells foul (indicates root rot or bacterial growth)

Checking Nutrient Levels (Optional)

If you have an EC or TDS meter:

• Initial EC (lettuce): 1.2-1.8 mS/cm (600-900 ppm on 500 scale)
• Mid-grow: EC may rise slightly as water evaporates faster than nutrients are consumed
• If EC rises above 2.5 mS/cm: Dilute with plain water to bring it back down

For beginners without a meter: Don't worry about it. Follow the nutrient label instructions at initial mixing, and let the plant do the rest.

5.5 Daily and Weekly Monitoring

Daily Checks (30 seconds)

• Visual inspection: Look for healthy green leaves, no wilting
• Water level: Note if it's dropping at a normal rate (good sign)
• Pests: Check undersides of leaves for aphids or whiteflies (rare indoors)

Weekly Checks (5 minutes)

• pH test: As described in section 5.3
• Leaf health: Look for discoloration, curling, or browning (nutrient deficiencies)
• Root check: Lift the lid and peek. Roots should be white or light tan, not brown or slimy
• Water level: Mark the level on the container with a marker to track consumption rate

What Healthy Growth Looks Like

Week 1-2: Slow growth, small leaves, establishing roots
Week 3: Growth accelerates, new leaves every 1-2 days
Week 4-5: Rapid growth, head of lettuce forming
Week 6: Mature, ready for harvest

If growth stalls or leaves yellow, see Module 6 (Troubleshooting).

5.6 When to Harvest

Lettuce is ready to harvest when:

• The head has reached full size (6-8 inches diameter for most varieties)
• Leaves are crisp and vibrant green
• Before the plant bolts (sends up a flower stalk)

Harvest timing by variety:

• Buttercrunch, Bibb: 45-55 days from transplant
• Romaine: 55-65 days from transplant
• Leaf lettuce (oak leaf, red leaf): 40-50 days from transplant

How to Harvest

Full harvest (one-time):

1. Cut the plant at the base, just above the net pot
2. Rinse the lettuce under cool water
3. Store in the refrigerator in a sealed bag (lasts 1-2 weeks)

Cut-and-come-again (multiple harvests):

1. Cut outer leaves, leaving the inner growing point (heart) intact
2. The plant will regrow from the center
3. You can harvest 2-3 times this way before the plant exhausts itself

Bolting (Flowering)

If your lettuce sends up a tall flower stalk, it has bolted. This happens when:

• Temperature exceeds 75°F for extended periods
• The plant is mature and transitioning to seed production
• Daylight hours are very long (spring/summer)
• Stress factors (nutrient deficiency, root damage)

Choose bolt-resistant varieties (Jericho, Muir, Nevada) for warm-climate growing.

Once bolted, the leaves become bitter. Harvest immediately or compost the plant and start fresh.

5.7 Cleaning Between Grows

After harvest, clean your system before starting the next plant.

Cleaning Steps

Step 1: Discard old solution

• Pour out any remaining nutrient solution (safe to pour down the drain or use to water outdoor plants)

Step 2: Scrub the container

• Wash with hot water and dish soap
• Scrub away any algae or mineral buildup
• Rinse thoroughly

Step 3: Sanitize (optional but recommended)

• Fill with a 10% bleach solution (1 part bleach, 9 parts water)
• Let sit for 15 minutes
• Rinse very thoroughly (bleach residue will harm plants)

Step 4: Clean the net pot

• Remove old roots and growing medium
• Scrub the net pot with a brush under running water
• If reusing clay pellets: rinse thoroughly, optionally soak in 10% bleach solution, rinse again

Step 5: Dry and reassemble

• Let everything air-dry completely
• Store or reassemble for the next grow

Reusing Growing Medium

Clay pellets: Reusable. Rinse thoroughly between grows, sanitize if desired.
Coco coir: Compost after one use, use fresh coir for the next grow.
Rockwool cubes: Single-use. Discard or compost (some municipal composting systems accept them).

5.8 What's Next

You now know how to plant, maintain, and harvest your Kratky system. In Module 6, you'll learn how to diagnose and fix common problems, and where to go next as you expand your hydroponic growing.

Next Steps

Previous: Module 4: Materials and Setup
Continue to: Module 6: Troubleshooting and Next Steps

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