Kratky Mason Jar Herb Garden

At a Glance

How This System Works

The Kratky method is the simplest form of hydroponics — there are no pumps, no timers, and no electricity required. Each plant sits in a net cup inserted into the lid of a wide-mouth mason jar. The jar is filled with nutrient solution to just below the net cup, and as the plant drinks the water down, an air gap forms between the water surface and the net cup. Roots in that air gap absorb oxygen, while roots submerged in the solution absorb water and nutrients.

This "set it and forget it" approach is ideal for herbs on a kitchen counter. You mix nutrients once, plant your seedling, and come back in a few weeks to a thriving herb plant ready for harvest.

Why mason jars? They are inexpensive, widely available, and the wide-mouth size perfectly fits standard 3-inch net cups. Wrapping them with tape or paint blocks light from reaching the roots and prevents algae.

Materials List

Our philosophy: Use what you already have. Hydroponics does not require store-bought equipment. People around the world grow food this way using recycled containers, scraps of fabric, and seeds saved from last season's harvest. The links below are for convenience if you prefer to purchase, but we encourage you to improvise with what is available to you.

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All-in-One Kit (Optional)

If you want everything in one box and don't mind spending a bit more, this mason jar hydroponic kit includes 6 jars, planting baskets, growth plugs, and wicking cores. Just add seeds and nutrients.

Otherwise, gather the parts below. Most of them can be found in your kitchen right now.

Containers

Use what you have: Any glass jar or plastic container that holds about a quart of water works. Pickle jars, spaghetti sauce jars, yogurt containers, plastic coffee cans, even large drinking cups. The container just needs to hold water and block light from the roots.

If you prefer something uniform and clean-looking: Wide-mouth quart mason jars fit standard 3-inch net cups perfectly and look nice on a windowsill.

Net Cups

Use what you have: Cut the bottom out of a small plastic cup or yogurt container and poke holes in the sides with a nail or drill. It does the same job as a store-bought net cup. Some growers cut a hole in the container lid and just set the plant directly into a piece of sponge.

If you prefer the real thing: 3-inch net cups (25-pack) are inexpensive and fit wide-mouth jar openings.

Growing Medium

Use what you have: Perlite from an old bag of potting soil works fine. Small gravel or crushed stone that has been rinsed clean will also do. The medium just needs to support the plant and allow water to drain through.

If you want to buy: Expanded clay pebbles (Hydroton) are lightweight, reusable, and pH neutral.

Seed-Starting

Use what you have: A small piece of sponge or a cotton ball can hold a seed in place until it sprouts. Some growers wrap seeds in a damp paper towel to germinate, then transfer the sprouted seedling into the net cup. You can also transplant a small herb plant from a nursery or grocery store by rinsing the soil off the roots.

If you prefer starter plugs: Rapid Rooter plugs (50-pack) make germination nearly foolproof.

Nutrients

Use what you have: This is the one area where you do need to purchase something. Plants grown in water without soil need dissolved nutrients to survive. Plain water alone will not work long-term.

That said, a single bottle of hydroponic nutrient concentrate lasts months and costs less than a few trips to the grocery store for herbs. General Hydroponics Flora Series (3-part kit) is what we use and recommend.

Monitoring (Optional but Helpful)

Free approach: pH test strips from a pet store or pool supply section work. You can also observe your plants closely and adjust based on how they look and grow.

If you want precision: A digital pH and TDS meter kit takes the guesswork out of nutrient mixing and costs about the same as two bunches of grocery store basil.

Seeds

Use what you have: Save seeds from herbs you buy at the grocery store, trade with a neighbor, or check your local library's seed exchange. Many communities have free seed programs.

If you want variety: A 12-pack heirloom herb seed variety pack gives you basil, cilantro, mint, parsley, dill, chives, and more for a few dollars.

Light-Blocking Material

Roots must stay in the dark to prevent algae. Use whatever you have: black electrical tape, aluminum foil, a sock, a paper bag, spray paint, or even a strip of old t-shirt wrapped around the jar. Anything opaque works.

Tools

No power tools required:

• Scissors
• Measuring cup or syringe for nutrients
• Marker for labeling jars

Build Instructions

Step 1: Light-Proof the Mason Jars

Roots must be kept in the dark to prevent algae growth. Choose one of these methods:

• Spray paint: Apply 2 coats of black spray paint to the outside of each jar. Let dry completely.
• Electrical tape: Wrap each jar with overlapping strips of black electrical tape.
• Aluminum foil: Wrap each jar snugly with foil and secure with a rubber band.

Leave a small viewing strip uncovered so you can check the water level without removing the lid.

Step 2: Prepare the Net Cups

Fill each 3-inch net cup about one-third full with hydroton clay pebbles or perlite. This will support the starter plug and seedling.

Step 3: Start Your Seeds

• Soak rapid rooter plugs in plain, pH-adjusted water (pH 5.5–6.0) for a few minutes
• Press 1–2 herb seeds into the top of each plug
• Place plugs in a warm spot (70–75 degrees F) and keep them moist
• Seeds should sprout in 5–10 days depending on the variety

Tip: You can also transplant small herb seedlings from a nursery. Gently rinse all soil off the roots before placing them in the net cup.

Step 4: Mix the Nutrient Solution

Follow the instructions on your hydroponic nutrient kit:

• Use clean, room-temperature water
• Mix nutrients to half strength for herbs (herbs prefer lighter feeding)
• Target pH: 5.5–6.5
• Target EC: 0.8–1.2 mS/cm

You will need about 28 oz (830 ml) of solution per quart jar.

Step 5: Fill the Jars

Pour nutrient solution into each mason jar until the water level sits about 1/4 inch below the bottom of the net cup. When you place the net cup in the jar opening, the bottom of the starter plug should barely touch or come within 1/4 inch of the water surface.

Step 6: Assemble and Place

• Set the starter plug (with sprouted seedling) into the net cup
• Add more hydroton around the plug to hold it steady
• Place the net cup into the mason jar mouth
• Position the jars on a sunny windowsill (south-facing is best) or under a small grow light

Step 7: Initial Checks

• Verify the water level touches or nearly touches the bottom of the net cup
• Make sure the jars are stable and will not tip over
• Confirm light is blocked from reaching the nutrient solution inside the jar
• Label each jar with the herb variety and start date

Nutrient Guide

Herbs are light feeders. Over-fertilizing causes bitter flavors and leggy growth.

Water top-off rule: As the water level drops, do NOT refill to the original level. The air gap that forms is essential — roots in the air gap provide oxygen to the plant. If the jar runs very low, add plain pH-adjusted water (no nutrients) to about halfway.

Crop Suggestions

Estimated Cost

Tips & Troubleshooting

General tips:

• Harvest herbs by cutting stems just above a leaf node — this encourages bushier growth
• Replace the entire nutrient solution every 2–3 weeks for best results
• If one jar develops problems, it will not affect the others — that is the beauty of individual jars
• Basil and mint are the most forgiving herbs for beginners

Maintenance Schedule

Daily

• Quick visual check: do the plants look healthy? Any wilting or discoloration?

Weekly

• Check water level — if the jar is less than one-third full, top off with plain pH-adjusted water
• Inspect for algae — wipe away any green growth and reinforce light blocking

Every 2–3 Weeks

• Full solution change — dump old solution, rinse jar, refill with fresh nutrient mix
• Trim herbs — regular harvesting promotes new growth and prevents flowering

Monthly

• Inspect roots — healthy Kratky roots should be white and firm
• Clean or replace net cups if they develop mineral buildup
• Check that light-blocking material is still intact

Frequently Asked Questions

How often do you change the water in a Kratky mason jar?

For most herbs, you should do a full nutrient solution change every two to three weeks to prevent salt buildup and keep nutrients balanced. Between changes, you can top off with plain pH-adjusted water if the jar gets very low, but avoid refilling to the original level because the air gap that forms as the plant drinks is essential for delivering oxygen to the roots.

Can you grow herbs in mason jars without sunlight?

Herbs need at least six hours of light per day to grow well, but it does not have to be sunlight. A small LED grow light positioned a few inches above your mason jars and run for 12 to 16 hours daily is an effective substitute for a sunny windowsill, making this setup work in apartments, offices, or rooms without south-facing windows.

Why is my Kratky basil wilting even though the jar has water?

The most common cause is that the roots have not yet reached the nutrient solution after the water level dropped below the net cup. When the air gap grows too large too quickly, the roots dry out before they can elongate to reach the water. Refill the jar with plain pH-adjusted water until it just touches the bottom of the net cup, and the plant should recover within a day or two.

Do you need to add an air pump to a Kratky mason jar?

No, the entire point of the Kratky method is that it requires no pumps, air stones, or electricity of any kind. As the plant consumes the nutrient solution, an air gap naturally forms between the water surface and the net cup, and roots growing in that gap absorb all the oxygen the plant needs directly from the air.