Hydroponics, Life, Recycling

Growing Vegetables and Fruits Indoors Using Kratky Hydroponics System

As mentioned in my previous article about the skills I learned that I have found useful in this pandemic is growing food through gardening. Three days before my birthday, I asked a friend for ideas on how I could grow vegetables indoors, in a limited space such as my condo unit. That day I was having a hard time getting a delivery spot from online stores for vegetables and fruits. Desperate, I consulted my friend on how to go about urban gardening and then joined gardening groups, both local and international, per her suggestion. It’s through my friend and reading through posts from groups I’ve joined that I found out about hydroponics.

Hydroponics literally means feeding plants while irrigating, also known as fertigation among US farmers (Roberto, K., How-To Hydroponics, 4th edition). Adding nutrient solution or “nutsol” to water enables growers to help plants grow to its genetic potential thus, ensuring better harvest. Plants grown hydroponically fare better than those grown in soils because soils are affected by water runoffs, pests, pollution, and other changes in the soil and atmosphere. The plants’ roots also spend so much energy digging into soil to look for moisture and nutrients. With hydroponics, the water and nutrients are directly delivered to the roots under clean and controlled environment – thus, their energy can be redirected into producing leaves, flowers, fruits and vegetables. Where water is scarce, it is favorable to grow crops using hydroponics rather than subjecting the plants to the harsh soil conditons.

I was highly encouraged to do hydroponics by pictures of successful harvests from plants that were hydroponically grown in the groups. So I gathered more information about it by watching videos on Youtube and read articles that discuss the different types of hydroponics system. For a few days, I absorbed information like sponge; imagined how each hydroponics system would fit in my condo unit; and strategized on how I would need to adjust my furnitures to accommodate the plants.

An efficient hydroponics set-up should be able to satisfy the following requirements for plants to grow according to How-To Hydroponics by Keith Roberts:

1) Provide roots with a fresh, well balanced supply of water and nutrients;

2) Maintain a high level of gas exchange between nutrient solution and roots;

3) Protect against root dehydration and immediate crop failure in the event of a pump failure or power outage.

In the picture is my pechay plant showing healthy white root underneath the net pot. The white roots is a good sign that the plant is going to thrive. This pechay was grown from kitchen scrap whereas, the rest of my plants were germinated from seeds.

There are generally two types of Hydroponic Systems – active and passive. An active system includes a water pump that is used to re-circulate the nutrient solution from a reservoir while a passive system relies on capillary action, absorption, and/or the force of gravity to replenish roots with nutrient.

Kratky, the system that I’ve chosen to do for now, is a type of passive hydroponics system. It is easiest to set-up by beginners like me because it requires less material; allows grower to use just any jar available around; and does not require electricity to run.

These are the basic materials you would need to set-up Kratky at home: growing medium for seeds, nutrient solution, jar, seeds, sunlight/grow light and water.

(If you would like to read about the grow lights I used for my Kratky system, you can read about it here.)

Growing Medium

Growing medium are spongy/porous or loose materials where you germinate your seeds until they grow into stable seedlings and ready to be transferred in hydroponic box or jar. Ideally, you’d need to see at least two set of true leaves (~2 weeks from sprouting) before you transfer your seedling into your hydroponic jar in order for the plants to survive. For those two weeks, you need to keep the medium damp with water or the nutrient solution, also known as nutsol. There are so many types of growing mediums out there, the simplest would be damp tissue or brown paper to more complicated and pricey ones such as flexiplugs and rock wool. Do take note that the rate at which your seeds grow, or germination rate, will also depend on the quality of seeds you are planting. I sourced my seeds from kitchen scraps, some were given by Bureau of Plant Industry; while others came from my supplier of hydroponics supplies.

Pro Tip: To preserve your seeds’ germination rate high, store your unused seed packets in the refrigerator.

For growing medium, I am currently using rock wool, flexiplug, hydrotons, and hortifoam. The reason I’m using all four types all at once is because I’m currently determining which one will suit me based on budget and germination success rate. So far, I’ver germinated seeds in all these media. According to my urban gardener friends, coco peat or cocoir is also a great growing medium for seeds. I wanted to try it too but I couldn’t find any supplier near me. Below are photos of my growing medium:

These are hortifoam where I’ve planted seeds of basil, kalonji, lettuce and pechay.
Rock wool is my first growing medium. Rock wools are finely spun rocks with high absorption rate thus, growers tend to favor these material over any other growing media. In the picture are my two-weeks old lettuce and basil. Since my window is facing east, I expose my young plants to the sun from 6 to 10 AM.
In the picture is my newly acquired flexiplug where a cluster of basil has germinated. Flexiplugs are imported from US and consist of a mix of cocopeat and sphagnum moss. These plugs need to be handled carefully as they are soft and easily flatten when pinched. Flexiplugs are fairly new and currently becoming a new favorite among growers.

Germinate the seeds in slightly damp medium away from the light for two days then gradually expose the seeds to the light. After two weeks, the seedling can be transferred into the net pots over the solution. For cuttings, I used hydrotons as growing medium. Hydrotons are the rust orange balls around the flexiplugs in the photo above. These are made up of clay and formed into balls. Hydrotons are a little expensive but may be substituted with cheaper pumice stones, fine-size pebbles, or cocopeat. If you’re using the latter, you would need a mesh to catch the cocopeat at the bottom of net pot. The reason I love using hydrotons and pumice is because they are porous. You would need air to circulate around the roots of your plant and porous materials like hydrotons and pumice are just perfect for that. Hydrotons also effectively block off the light and the reason for that will be discussed in more details below.

Net Pots

Net cup or pot is necessary for any hydroponic system.

You would need net pots to hold the plant over the solution. Net pots vary in diameter, with smallest at 1.75 inch to as big as 12 inches. I use 2 inch net pots for most of my plants but I plan to transfer my tomato and bell pepper to 3 inch net pots when they grow bigger. If you can’t find any supplier near you who sell net pots, you can substitute with plastic cups, yoghurt cups, and styro cups. Cut a few slits on the side and base of the cups for the roots to reach the solution when they grow longer and for the nutrient solution to reach the growing medium. The cups should also fit the mouth of your hydroponic box or jars.

Here’s a makeshift net pot I made out of empty yoghurt cup containing a flexiplug, hydroton balls, and my 2-days old mustard seedlings.
I used a 2-inch net pot to contain this pechay bulb from kitchen scrap and some hydrotons as growing medium.

Hydroponics Box and Jars

Due to community quarantines and lockdowns, I had a difficult time sourcing the materials I would need for my Kratky set-up. It took me a while to search for suppliers that still deliver despite the quarantine and I’m lucky to have discovered CRS Hydroponics Enterprises – where I got my nutsol, net pots, seeds, and growing media from. For my hydro box and jars, I’ve simply used the empty jars, containers, and ice cream tubs I have at home. Kratky hydroponics system allows for creativity and resourcefulness.

I’ve used different containers to grow my plants. I intend to do hydroponics as cheap as possible and environment-friendly. Good thing I haven’t thrown away my empty ice cream tubs and glass jars because I was able to plant all my seedlings in them.

For the ice cream tubs, I cut away roughly circular holes on the cover that would fit the net pots using my ever reliable Leatherman multi-tool. I also painted some of the tubs white using the leftover white acrylic spray I had lying around. Painting the tubs white helps turn these containers opaque to minimize or completely obliterate light. I have morning light as my window is facing east so I have to ensure none of the light gets inside my hydro boxes and jars. The last thing you’d want is for the light to enter your containers as this will encourage algal growth inside. If algal growth is left unchecked, it will result to root rot and plant death due to competition in the nutrients. You’d know you have algal growth in your box if the water starts smelling like drainage canal.

Using acrylic spray, I painted these ice cream tubs white to ensure that none of the light pass through. Light will result to algal growth inside which can result to root rot.

When transferring the seedling, it is ideal to include the growing medium in the net pot because isolating the seedling from its growing medium such as rock wool can potentially damage the roots of your plant especially if you are a beginner like me. So what I did in order to lessen the impact of transferring the plants was to put the seeds in the growing medium and put it inside the net pots. I then sprayed water on the medium every morning and afternoon to ensure these don’t dry out in the summer heat. I then inserted the net pots in my fabricated hydro jars and boxes containing nutsol.

When my acrylic spray had ran out, I wrapped my glass and plastic jars with aluminum foil or duct tape and then wrapped with my old socks for aesthetic purpose. Below are photos of the containers I’ve used for my Kratky.

I used this 1-L container and cut two holes on the side to accommodate two plants. I haven’t added foil around it to show you how the net pots look inside with the nutrient solution. I also realized that the solution was too much and was drowning my rock wool and plant so I poured out some by opening the cap and tilting the jug carefully.
Inside this canvass potato bag is a glass jar containing half-strength nutrient solution (this means diluted by 50% more water) and cuttings of sweet potato from kitchen scraps. The canvass bag has strings that I have tightened around the jar’s mouth to ensure less light goes in. Then I tied paracord around the handle and hung the plant on my window grill using a S-hook.
For my string bean, I re-used a 1-L milk carton, cut around a hole beside the cap and inserted my net cup containing the seedling and rock wool. The cap can then be opened to peek through when assessing the level of the nutsol and also for refiling when the solution becomes too low.
The PET container on the left was painted white using acrylic while the liquid soap jug on the right was covered with aluminum foil. Both containers contain pechay cutings from kitchen scraps and then covered with my old Mr. Froggy socks for aesthetics and also to ensure none of the light goes inside the containers.
These are my two weeks old pechay grown from seeds. I also used old socks to cover these glass containers.

Nutrient Solution

I am currently using Master Blend for nutrient solution although I have also bought Veggie Sol and Snap to try too for future comparison. I got my Master Blend and Veggie Sol sets from CRS Hydroponics Enterprises while the Snap hydroponics solution A and B I got from Green Grow Cycle. Both sellers have their official pages on Facebook. Veggie Sol and Master Blend sets come with Calcium Nitrite and Magnesium Sulfate. There are other brands of nutsol out there such as Yamasaki and Zennor but for now, I plan to use these three brands until they run out. After that, I might try Zennor and Yamasaki as these are inexpensive and readily available locally.

Master Blend was highly recommended by growers I’ve watched on Youtube and those at international Facebook groups I’ve joined. Snap solution, developed by agriculturist at UP Los Banos, is locally produced and commonly used by local growers. I plan to use Veggie Sol when some of my plants start showing flowers and fruits alongside Snap solution for comparison. I will write a more detailed review of these nutrient solutions in the coming months.

A set of the Master Blend can make 19 liters worth of nutsol. The set comes with instruction on how to prepare it. To make the solution, prepare 19 liters of water in a bucket. The nutsol set has 3 sachets – 1 sachet each of Master Blend powder, calcium nitrite and magnesium sulfate (Epsom salt). Each sachet of nutrient needs to be dissolved in separate containers with water taken out of the 19-L volume of water so that means you should have three separate solution. Leave each solution for 5 minutes. Then add each solution into the bucket of water and mix thoroughly. The mixture is now ready for your Kratky system.

I have these three types of nutrient solution in my stash. I’m planning to test each one and then write about my comparison in the coming months.

When the seeds started sprouting, I gradually exposed the young seedling to the sun and wait for them to grow more leaves. I put my plants on the top of our aircon unit as we don’t have balcony. To maximize the limited space on my aircon, I take the net pots out of the jars and boxes and put them in plastic containers to expose to the sun every morning. Once they start showing longer roots that are visible underneath the rock wool and net pot, I put the net pot inside smaller jars and fence them beside the window as in photo below. I only expose my plants from 6 to 10 AM as it gets too hot beyond 10 AM. The one thing I also avoid, as advised by growers in my groups, is the solution getting too hot as this can kill the plant. I plan to buy thermometer and pH meter to measure temperature and pH of the solution. The ideal pH in which most plants grow is between 6 and 7. I heard that if using Snap solution, there is no need to measure pH. This is possibly the main reason why local growers prefer it over other nutsol brands.

When my seedlings were smaller, I put the net pots in microwavable plastic containers and put them outta my window over our aircon unit to expose to the sun from 6 to 10 AM. I spray the rock wool with water and some nutsol prior to exposure. Beside my small plants is this pot of highland “kangkong” grown in soil.
I’ve had this fence for two years now and didn’t know what to do with it until my seedlings started growing roots underneath that they needed to be transferred to small jars for sun bath as putting the net pots on plastic containers as in photo above might damage the young roots. Good thing my 1-L milk carton and small jars fit perfectly in this fence.

I’ll keep you posted on the status of my plants. For now I’m just excited to see them grow. I hope to harvest my lettuce and pechay in the coming weeks. If you want to try Kratky Hydroponics, feel free to send me a message below if you have questions.

Update: One of my 2 weeks old pechay has shown droopy leave and I’m worried that the Philippine summer heat is too much for it so I added these black net curtains originally designed for doors to ward off insects just to filter off the light a bit. I hope this works, honestly, since all garden supplies shops are closed right now so I can’t get a decent garden net.

Added net curtains to filter some of the sunlight off my plants.


Here’s our recent video about how we use Snap nutrient solution for our Kratky hydroponics system at home. 🙂

Since a lot of people from outside the Philippines are asking where they can possibly get some of the products mentioned here, I am including my affiliate links with Amazon below. Please take note that by buying these stuff through my affiliate links, I get a bit of commission that will help me fund this website and keep it up and running.

Kratky Hydroponics system kit
Beginner guide book

9 thoughts on “Growing Vegetables and Fruits Indoors Using Kratky Hydroponics System”

    1. Hi, Cha. If you are growing them on a roof deck under full sun, best to cover the jars with insulating materials and roof them with some netting that can filter off the sun by as much as 30-50%. If not insulated, the water will heat up and cook your plants. There are UV plastic cover that can be bought in garden supplies but even with that roofing, you’d still need insulating materials around your jars. I have a friend who has circulating/active hydroponics system without insulation and all her plants died because of the summer heat. 😦


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