This is my recipe for growing hydroponic plants using the Kratky method. I want to emphasize that this recipe is NOT an experiment. It is simply a procedure to show you how to grow plants without soil. Depending on your child’s experimental setup, you may not even use this section if they’re only growing plants in soil.
MATERIALS – get these ahead of time. I include Amazon links, and once you buy the initial setup, it will last you a long time. My explanations are in italics.
- Peat pellets ($23/100) – I use these pellets to start my seedlings because you can then easily pop them into net pots once they’ve germinated.
- Seeds – I highly suggest getting fresh seeds, because older seeds either won’t grow, or they take forever to germinate (I know from experience). Kratky method is best for leafy herbs and salads to start (my basil looks AMAZING), although there are folks who grow tomatoes, strawberries, etc. (you have to adjust the fertilizer content and get bigger containers if you do). My instructions here are for herbs and salads. If you’re not looking to grow a harvest, beans and lentils will work for the next few weeks. BTW – you can also use rooted plant cuttings – I do this a lot with my mints.
- Shallow trays or plastic shoebox containers – I save plastic trays that I get from restaurant takeout or Costco packaging. These are great for starting your seeds.
- Hydroponic fertilizer set ($35) – You put this liquid fertilizer in the water to make a nutrient solution for your plants. Store these bottles out of the light. A little bit will go a long way!
- Net pots ($13/25) – These are pots with holes in them so that the roots can grow out to reach the water. You can drill lots of holes in ordinary pots to get the same effect, but it’s time consuming. These are reusable.
- Clay pebbles ($15) – These are added to you pots to keep the plants from moving around. These are reusable.
- Wide mouth mason jars ($12/6) – I include the Walmart link because they are ridiculously expensive on Amazon. These are just your ordinary canning jars.
- Foil or paper, rubber bands or tape – This covers the jar to prevent algae from growing in your nutrient solution.
- Water – You need really good water to make your nutrient solution. If you have hard tap water or use a water softener, it will affect the quality of your nutrient solution, and your plants may not grow well. Either filter the water, or buy 2 gallons (or more) of distilled water. Of course, this could also be a great experiment! Your child can compare nutrient solution made from tap water vs. nutrient solution made from filtered water to see if one is better than the other.
- 1-5 gallon bucket or container – For mixing your water with fertilizer to make the nutrient solution.
- Optional: LED grow light ($75) – I’ve run experiments with different grow lights and have found that Root Farm’s light works best for my indoor garden. One light can grow approximately 12-15 plants in mason jars.
Procedure
Start Your Seeds
- Take one of your shallow plastic trays and lay out the number of peat pellets you need.
- Add water to hydrate the pellets. I’m an impatient person, so I add warm to hot water to get them to hydrate faster.
- Wait until the hydrated pellets are cooled. Then put your seeds into them. You want to place 1-4 seeds, evenly spaced apart. The number of seeds depends on the kind of plant you are growing. My rule of thumb: 1 salad seed, 1 mint, 3 basil seeds, or 3-4 cilantro seeds.
- Put your tray in a dark place for 1-2 days. Then take them out to sprout. This may take 1-2 weeks.
- Make sure your pellets don’t dry out, or it will kill the seedling.
Make Your Nutrient Solution
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- Measure out 1-5 gallons of your water. I make my nutrient solution in batches so that it can be used all at one time. However, you can also mix and store the solution in a carboy or giant sports cooler as long as it’s not exposed to light (which will cause algae growth).
- Shake the FloraMicro bottle. Then add 1 teaspoon for every gallon of water that you have. Then mix it well. The fertilizer set comes in 3 concentrated bottles that cannot be mixed together. You need to add and mix each one separately to the water, starting with the red FloraMicro bottle.
- Shake the FloraGro bottle. Then add 1 tsp for every gallon of water that you have. Mix well.
- Finally, shake the FloraBloom bottle. Add 1 tsp. for every gallon of water that you have. Mix well.
Set Up Your Net Pots
- Once your seeds have started germinating, it’s time to put them into your net pots.
- Wash your clay pebbles so that the water runs clear.
- Carefully add the clay pebbles around your net pot so that it holds the peat pellet in place.
- Add more clay pebbles to try and block out most of the light coming in from the top of the pot (to minimize algal growth once you put them in your jars).
Set Up Your Mason Jars
- Add enough nutrient solution to the jar so that at least part of the peat pellet will be submerged in the solution. This will give the seedling roots enough time to grow out and down without drying out.
- Add the net pot with your plants and clay. Adjust the level of your solution accordingly. Screw on the metal ring part of the jar lid.
- Then cut enough foil or paper to cover around the jar. This will keep the light away from the solution to prevent algae from growing. Tape or use a rubber band to keep the foil/paper in place.
- Set under a grow light or by a sunny window, and check the solution at least once a week.
Refilling the Jars
- Check the level of your plant solution at least once per week. As the level of the water goes down, the roots should follow.
- Refill when the solution is almost used up. Fill about half way, leaving some of the roots exposed to air.
VERY IMPORTANT: Always keep a pocket of air between the roots and solution. DO NOT cover all the roots with solution. Your plant roots need this air to grow. Otherwise, the plant will suffocate and die.
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