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Mason Jar Hydroponics: Easy Indoor Growing!

A spinach plant thrives in a glass jar of water

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If you’re curious about hydroponics but don’t want to invest in a large-scale, complex system, you’ve still got options!

Mason jar hydroponics is a cost-effective, low-effort way to start growing hydroponically. And you probably already have most of the necessary components!

In this article, you’ll learn all you need to know about this super-simple method:

  • How it works
  • What it requires
  • Troubleshooting tips
  • What you can harvest from doing hydroponics in a Mason jar

Let’s jump in!

Hydroponics in Mason jars is an adaptation of the original Kratky method of hydroponics, which involves growing plants without soil in five-gallon buckets.

If you’re interested, you can read about the technical/scientific aspects in Professor Kratky’s original research paper.

For our purposes, quart-size Mason jars rather than buckets get filled with a solution of water and nutrients.

Just like this:

A quart-size Mason jar sits on a sunny countertop

Then, seedlings are suspended from a plastic net pot in the lid so that their roots touch the water and can uptake hydration and nutrients.

Other hydroponic or aquaponic setups require pumps to circulate water and some kind of aeration system.

RELATED: Hydroponics and aquaponics are alike in several ways, but they are NOT the same. Learn more in our post Hydroponics vs Aquaponics

However, the Kratky method is entirely passive.

At the beginning of the process, you, the planter, add enough nutrient solution and water volume to the bucket or container to sustain the plant until it’s ready for harvest.

Mason jar hydroponics makes things very simple, straightforward, and hands-off. This is a great option for a home growing system due to its simplicity and the availability of all the necessary parts.

Plus, there are a huge variety of vegetables you can grow using Mason jar hydroponics, which we outline in detail in our post on what you can grow using the Kratky method

With a sunny countertop and a little bit of up-front effort, you’ll have yourself an indoor garden.

Materials Needed

Aside from a quart-sized Mason jar and corresponding ring, there are a few basic supplies you’ll need for hydroponic growing.

Nutrients

Because there is no soil in hydroponics, plants receive all their necessary nutrition from a liquid nutrient solution that you initially add to the water. 

Select a liquid nutrient specifically engineered for hydroponics; a standard liquid fertilizer for houseplants or outside gardens will not provide the same results. 

General Hydroponics offers pH-balanced nutrients fortified with all the macro and micronutrients a plant needs to grow. 

Another great maker of hydroponics nutrients is Root Farm, with a “Base Nutrient” and “All-Purpose Supplement” combo to provide all necessary nutrients.

Both of these options, and many others, are available on Amazon.

Seeds

The Kratky method in general works best with leafy greens and lettuce, and Mason jar hydroponics is no exception. 

Leafy greens tend to:

  1. Grow quickly
  2. Stay small in size
  3. Reach harvest in a short time from their initial planting
  4. Have lower nutrient demands (no fruits or flowers to support)

To get the best harvest from your Kratky method Mason jar, you’ll need to start with good seeds. Botanical Interests is an outstanding source for a wide variety of seeds, including many organic and heirloom options. 

Here are some seeds you can get from Botanical Interests that work great for Mason jar hydroponics:

These will all grow from seed to harvest in about 30 days.

Grow Medium

Although a hydroponic system is soilless, it still utilizes a growing medium to anchor the plant roots. 

Rock wool (like this brand on Amazon) is a very popular medium in hydroponics. It consists of melted volcanic rock that has been extruded into a matrix of small fibers.

Hydroponic growers usually use rock wool in cube form, like this:

A gardener holds a seedling growing hydroponically in a rock wool cube.

Its popularity is mainly due to how well it absorbs liquids and nutrients while also allowing oxygen to access the roots. 

Rock wool is also useful to a home hydroponics grower because you can start seeds directly in it, instead of germinating and raising a seedling in soil and transplanting it into a soilless medium.

Also, rock wool is somewhat reusable. If you thoroughly rinse a block after removing a plant from it, you’ll be able to start and grow another plant in it.

Other options for your planting medium are Rapid Rooter Plant Starters or clay pebbles, both of which are also available on Amazon. 

Net Pot

A net pot suspends the plant and planting medium above the water, allowing the roots to grow down through slits in the side.

Here’s what it looks like in action:

A gardener holds a hydroponic net pot with a strong root system growing out of it.

Net pots come in a variety of sizes, most commonly 2-inch and 3-inch diameter. They’re pretty inexpensive and easy to find. 

If you’re using a narrow-mouth jar, you’re better off getting 2-inch net pots.

For wide-mouth jars, both 2 and 3-inch pots work fine, but you may need to make a plastic support ring if you use 2-inch ones (covered in the next section).

These 2-inch ones are a good option, and if you want to go a little bigger, consider these 3-inch ones

Plastic “Ring”

If you’re using a wide-mouth Mason jar, you’ll need to create a ring to hold your net pot in place at the jar’s mouth.

(If you’re using a narrow-mouth jar, you can probably skip this step. But make sure to verify that your net cup fits securely first.)

But don’t worry- it’s not hard!

Scavenge a sheet of rigid plastic from food packaging and use it to create your support ring. Lids from large yogurt containers or packages of fresh greens work great. 

  1. Lay the lid of the jar down on the plastic and use a marker to trace around it.
  2. Cut out that circle.
  3. Then, lay the rim of the net pot in the center of that circle and trace around it.
  4. Cut out the smaller inner circle. 

This plastic ring should fit over the mouth of the jar, and the net pot should hang securely from it.

Paint or Other Light-Blocking Layer

To prevent the growth of algae, cover the outside of your jar with something that blocks light.

A black or dark-colored spray paint works best. It will look something like this when you’re done: 

A Mason jar painted black.

If you’d rather, you can also wrap your jar in a bag, paper, aluminum foil, or even duct tape.

Whatever you choose, make sure to apply your light-blocking layer on the outside of the jar. 

Planting Your Seeds

If using rock wool for your growing medium, you’ll want to soak it in filtered water for a full day before planting any seeds in it. This allows it to completely hydrate.

You can use a hole-less seed starting tray to soak the rock wool and then to hold it while your seeds are germinating.

After the rock wool has soaked for a day, place 3-5 seeds in the center of each square plug of rock wool.

To help speed up germination by quite a bit, you can purchase a heating mat to use under the tray and a humidity dome to trap moisture above it.

You don’t need light to sprout seeds. But once they have popped up above the surface of the rock wool, they will need strong light to continue generating energy to grow large enough for planting in the Mason jar.

Place the tray in a sunny window or beneath a set of these small grow lights. You can also choose to buy a humidity dome with a built-in light to make things even more foolproof.

Once your seedlings have produced a root that reaches past the bottom of the plug, you’re ready to transfer it over to the net pot and place it in the Mason jar.

Which leads to the next point: getting your jar ready for growing!

Prepare Your Planting Materials

Sanitize your jar to reduce the number of microbes on the surface. Submerging it in boiling water for a few minutes and allowing it to air-dry is the easiest method.

NOTE: Always sanitize before applying any paint or adhesive for a light-blocking layer. 

After sanitizing and getting your light-blocking system in place, place your plastic support ring and net pot in the mouth of the jar.

Setting Up Your Mason Jar Garden

One of the most crucial elements of any hydroponic system is the nutrient solution.

Add nutrients to water to create a nutrient solution. This is what will feed the plant as it grows.

Check the labels of your nutrients for dosage directions, and make sure to use pH-balanced water. Filtered or distilled water is the safest choice.

Fill the jar until the water touches the bottom of the net pot. As the water evaporates, the roots of your seedling will follow it down.

Place the jar in a place that gets good sunlight, like a windowsill on a south or east-facing window.

Or, if your home doesn’t receive much strong sun, you can use the grow lights we talked about earlier to supplement that light that you do get.

Harvesting

Once your plants have several strong leaves, you can start to harvest and enjoy the fruits of your labor.

This will usually be about 4 weeks or so after your seeds germinate, and your plant should look something like this: 

A lettuce plant growing in a hydroponic set-up

You can harvest the entire plant all at once or just a few leaves at a time to let the plant keep growing and pushing out more leaves. 

Instead of breaking off leaves, use a pair of sharp, clean scissors to snip them off. This will prevent any stress or displacement of the roots from tugging or moving.

The plant produces new leaves from the central stem, so always harvest leaves from the outside first.

Potential Problems to Look Out For

Growing a Kratky method mason jar may be simple, but it’s not immune from developing the occasional problem. 

Here are a few you may run into:

Seeds not sprouting/growingIf your seeds fail to germinate, it’s probably due to a lack of heat or a lack of humidity

Make sure that your seedling tray is a warm spot in your home. Use a heating mat underneath the seed tray to warm up the planting medium, and place a humidity dome over it to trap moisture. 

You should also be careful to keep the planting medium in the seed tray consistently damp, watering as frequently as needed.

Try again with fresh seeds, making the necessary adjustments. 

Low water level – The water in your Mason jar will inevitably evaporate and usually the plant’s growth will be able to keep up with it.

If, however, the water is evaporating so quickly that the roots are being left behind, you can lift out the net pot and add a bit more water.

But when you do add water, don’t submerge the entire root system. Instead, make sure to add just enough to keep the bottom of the roots wet.

That way, they are still able to absorb oxygen without drowning.

Leaf discoloration Leaf discoloration can be a result of improper nutrient content or a too-cold environment

If you find your leaves yellowing or browning, double-check to make sure that you added the right amount of liquid nutrients to the solution.

You may need to add more nutrients or dilute your solution with more water.

Lettuces and greens like cool temps, but not cold ones. If your jar sits right next to a window where it may be experiencing cold drafts at night, try moving it back a bit into a more sheltered (but still sunny) spot.

Bad smellIf your water starts to smell bad, it’s probably growing some mold or algae

When you smell an odor, remove whatever is harvestable from the plant and discard what’s left of it, the rock wool cube and the water.

Thoroughly clean and sanitize the jar and net pot before re-using for your next round of Mason jar hydroponics.

When to Start a New Jar

Your leafy greens or lettuce will take a few weeks to reach maturity, after which they will be harvestable for three to four weeks.

After that point, the plants will naturally start to decline and become less leafy as their energy goes into setting seed. 

You can prolong your harvest by removing any seed heads that form and keeping your jars in a slightly cool spot.

Occasionally replenishing the water and nutrients in the bottom of the jar will also keep a plant alive and productive for a bit longer–just be careful not to overdose!

Once your plant’s growth has slowed down considerably, it’s time to discard the spent plant and water. 

Rinse your rock wool, clean and sanitize your jar and net pot, and start all over!

Frequently Asked Questions about Mason Jar Hyrodponics

Hydroponic lettuce is healthy, especially if you choose only high-quality nutrients to feed them with. The better fed your plants are, the better fed you will be.

Plants can grow for a time in nothing but water, but eventually they will peter out and die because there just isn’t enough material there for them to keep building their cells.

A plant needs to obtain macro and micronutrients to stay alive, including nitrogen, phosphorous and potassium, which just aren’t in plain water to any high degree. 

Hydroponics can produce extremely healthy and productive plants, but so can soil-based growing. Plants are naturally attuned to growing in soil, and so in a sense they will always grow more easily there.

But when a hydroponic system is set up and maintained properly by an attentive gardener, it can use a limited space to produce a lot more food in a lot less time than growing in soil.

Final Thoughts

Hydroponic growing doesn’t have to be an expensive set-up that takes up a lot of space. 

For small leafy crops, your countertop and a simple Mason jar will provide you with fresh food and a sense of accomplishment! 

Are you ready to give Mason jar hydroponics a try? What would you grow, and do you have any other questions?

Let us know in the comments!

 

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About Erinn Witz

Hi! I’m Erinn, a Midwestern gal who’s just as interested in honing my gardening skills as you are. I’m here to show you that if I can do this growing thing, seriously, YOU can too! 

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