The Kratky Method Mason Jar

Kratky Mason jar

A Kratky Mason jar system is the simplest way to get your feet wet in the world of Kratky hydroponics. Using just a few cheap (or free) materials, you can construct a simple hydroponic food growing system. The Kratky method of hydroponics makes food-growing possible for anyone, anywhere.

Similar setups can be created with all kinds of common household items; I have used yogurt cups, gravel, coffee cans, stemless wine glasses, ceramic mugs, and more as materials for free Kratky setups. You are only limited by your imagination. Today, however, I will provide you with a construction guide using basic hydroponic supplies and household items. The hydroponic supplies are readily available at reputable online retailers or your local hydroponic store. 

Shopping at your local hydroponic store will usually result in lower costs for small setups like these, as you aren’t required to purchase large packs of net cups and nutrients. Even more, you will be supporting a local business and keeping your money in your community. 

Now, on with the show. Here is what you need:

  1. Wide-Mouth Mason Jar
  2. 3” Net Cup
  3. Hydroton Clay Pellets
  4. Hydroponic Nutrients
  5. Lettuce/greens seedling

To construct the Kratky Mason jar growing system, insert the net cup into the top of the mason jar. Then, fill the jar with water to approximately ⅓ of the way up the net cup. Take the net cup out of the mason jar and mix in your nutrients. Reinsert the net cup, filling it with hydroton. Finally, insert your seedling. Wait a few weeks and enjoy the leafy greens of your labor! 

Now, let’s break this down and discuss each item on our materials list. The wide mouth 32 oz. Mason jars are a good size for most greens, and they perfectly fit the 3” net cup. Depending on the variety of plants and other factors, you may not have to replace any water and can truly ‘set it and forget it’. 

The 3” net cups should be very affordable from your local hydroponic store. If you can’t seem to find them, start looking around your house. I have re-used and modified small plastic food containers to perform the function of a net cup. 

The hydroton clay pellets are the best material I have found to support the base of your plants. They are lightweight, providing the necessary support for the plant without crushing the roots. Other similar materials can be used, such as gravel or pebbles, especially if you are aiming for a free Kratky setup. However, these materials may pose problems and will be more difficult to work with. If hydroton is available to you, go with that. 

Kratky method “fertilizer”, or nutrients, comes in many varieties. I prefer an A-B dry solution, but liquid solutions do have their benefits. If you are not sure if you will continue the hydroponic hobby and want simplicity, you can opt for an all-in-one liquid solution. You will want a balanced solution that is rated for leafy growth (as opposed to blooms), such as FoxFarm’s “Grow Big” or any other solution formulated for lettuce and greens.

Alternatively, I have used compost tea with success in Mason Jar and 5 Gallon Bucket Kratky setups. While it may be more difficult to measure and control the levels of specific nutrients in the compost tea solution, I find that greens and other quick-growing plants do not mind. I use an approximately 1:4 ratio of compost to water volume ratio. For example, try steeping 1/2 cup of compost in 2 cups of water for about 2 to 3 days. Strain the compost through a cheesecloth and use the resulting liquid as your hydroponic solution.

Lettuce (as well as most greens) seedlings should be transplanted into your Kratky jar when they have formed their first true set of leaves and are about 3 to 4 inches tall.

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