Growing Basil in a Mason Jar

 

Growing Basil in a Mason Jar
Rockwool + Net Cup Kratky Method

This is one of the easiest ways to grow basil indoors. It’s basically a simple “no pump” hydroponic method: the plant drinks from the jar, and the upper roots stay exposed to air so they can breathe.

Hydroponic basil in my basement.

What You’ll Need

  • Basil seeds

  • Rockwool cube (pre-soaked)

  • Net cup (net pot)

  • Quart (32 oz) mason jar

  • Mason jar ring + lid

  • Water

  • General Hydroponics MaxiGro

  • Optional: a warm spot + bright south-facing window or a grow light

Step 1: Prep the Rockwool Cube

  1. Soak the rockwool cube in water until fully saturated.

  2. Put the cube into the net cup, then place the net cup into the mason jar.

  3. Add about 1 inch of plain water to the jar.

PRO TIP: Use a wet toothpick to pick up two basil seeds and drop them into the hole in the rockwool cube.

Step 2: Germinate (3 to 5 days)

  1. Seal the jar using the mason jar’s original ring and lid.

  2. Place the jar in a warm location to germinate.

    • The top of the cupboards is a great spot because it’s often warmer.

  3. In 3 to 5 days, you should see sprouts.

Basil is super easy to germinate and grow, which is why it’s a perfect “first hydro plant.”

Step 3: After Sprouting, Switch to Airflow

Once the seeds sprout:

  1. Remove the ring and lid.

  2. Set the lid aside.

  3. Put the ring back on, this helps the net cup stay stable as the basil grows, but keep the top open for airflow.

Step 4: Feed Until You See Roots

Until you see roots extend below the rockwool:

  • Twice per day, pour a little nutrient solution over the cube:

    • General Hydroponics MaxiGro mixed with water per label directions.

  • You’re waiting for the moment you can clearly see a root poking down below the cube.

Step 5: Set the Water Level the “Kratky” Way

Once you see a root coming out below the cube:

  1. Fill the jar with nutrient solution so the liquid is just touching the root not drowning the whole cube.

  2. Keep the liquid barely touching the roots as they grow down.

After the root system develops:

  • You can keep the jar about 1/2 full, leaving the upper 1/2 of the roots exposed to air.

  • This is important: roots need that air gap for oxygen, or growth slows and problems start.

Step 6: Light = Big Basil

For vigorous growth, basil needs strong light:

  • Best option: bright south-facing window

  • Or: a grow lamp placed close enough to keep the plant compact and leafy

With adequate light, you’ll get fast growth and plenty of basil for cooking or giving away to friends.

Step 7: Daily Top-Off

As basil gets larger, it drinks a lot.

  • Be prepared to check and top off daily

  • Keep the jar around 1/2 full, maintaining that air gap above the water line

If the level drops too far, the plant can dry out fast.

PRO TIPS

Blackout the Jar: Cover the glass jar with aluminum foil, or paint the jar silver before you start. This blocks light, which prevents algae growth and also helps reflect light and keep the jar water cooler. If you leave the jar uncovered, algae will grow. Algae can compete for nutrients and make the system messy.

Light: Give it 12 to 16 hours of light per day if you’re using a grow lamp.

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