originally from: Hydroponics for Beginners: Start growing your plants now
Which hydroponic system is the most cost-effective?
The most cost-effective system for hydroponics, hands down, is the Kratky method. The Kratky system is named after the professor from the University of Hawaii who pioneered it, A. B. Kratky.
The Kratky method is incredibly simple because you don’t need any special equipment or pumps. You just need a sufficient amount of water and nutrient solution, and it’s set and forget.
The Kratky method works by providing the plant all the water and nutrients it will need from the beginning of its life to harvest in the first go.
At first, the water level will be high and the bottom of your holder will be submerged in it. As the plant roots grow and the plant uses up the water, the water level drops, and the roots keep extending downwards into the lowering water level.
The advantage of this is that the oxygen that you’d otherwise need to bubble into the water using an air pump gets there because of the increasing gap between the plant and the water level.
The atmosphere is automatically refilling the oxygen for you!
You’d need a roughly one-gallon bucket to grow a single lettuce plant.
Of course, this is for growing on a small scale. If you wish to grow a lot more things, then you’ll need a lot more space for growing using the Kratky method. For 20 plants, you would need 20 buckets, or at the very least, 20 gallons of storage space and enough surface area on your container to fit 20 plants.
20 gallons is still manageable, but what about 100 plants? If you’re planning to grow on a commercial scale, you’d need a bigger and more complex system, especially if you’re tight on space.
Since we are growing hydroponically, it’s no big deal if the plants are crowded a little – there are more than enough nutrients and more than enough water to go around.
Setting up a Kratky grow is incredibly easy.
First things first, you’ll have to germinate your seeds. You can germinate in rockwool cubes, coir bundles, or even thick cotton swabs. Anything soft and porous that your plant roots can penetrate into will work.
To germinate, thoroughly wet your growing medium – e.g. the rockwool.
Then poke a tiny hole in the top and drop some seeds into the hole. It’s a good idea to drop multiple seeds in a single cube to “guarantee” that at least one will germinate.
Keep the seeds in a humid place and make sure the medium does not dry out. It does not need to be soaking wet – indeed, it shouldn’t – but it should be damp at all times and not dry out.
Until the first shoots pop out, you don’t need light either, so you can store them in a closet or something too. To lock the humidity in, put a plastic cover on top of the rockwool cubes.
In one to three days, you’ll see shoots come out. Once the shoots are out, make sure they have very good exposure to light. You can use grow lights like an LED bulb or a T5 tube light, or if you have a sunny window, the windowsill will do fine, too.
South-facing windows will generally receive consistent sunlight in the Northern hemisphere, especially during winter months.
It will take about 10-14 days for the germinated seed to develop its first set of true leaves(proper leaves with visible veins).
While you’re waiting for the seeds to germinate, it’s time to set up your growing bucket.
Since we’re building a cheap setup, you can really use any bucket you can find. Use a bucket you have lying around, or go pick one up from Walmart or Target.
You can even use a large shoebox or plastic container, as long as the vessel you choose has a removable lid.
Ideally, you want at least one gallon of capacity for one head of lettuce, but if you can’t find something big enough, use something smaller and bear in mind you will have to refill it once the water level drops too low.
Next, cut a hole in the lid a little smaller than the widest part of your net cup. This will ensure that the net cup won’t fall in all the way.
The best way to do this is to use a box cutter or knife and cut a smaller circle than you need, then start lightly trimming away to get the right size.
If you’re going to grow your plant outside, you want to try to have as little sunlight penetrate the inside of the bucket as possible. This is to inhibit the growth of algae and other bacteria.
So if your bucket or vessel is transparent or clear, cover it with some dark paper or give it a coat of dark spray paint.
If you’re growing inside on a windowsill or using lights, you won’t have this issue.
With your lid and bucket ready, it’s time to transplant the seeds once they’ve germinated and sprouted leaves.
Once your seedlings have two to three true leaves, they’re ready to be transplanted.
When the seedling first sprouts, it will form two or three leaf-like structures – these aren’t leaves, but the nutrient stores the plant will use in the early days of its life.
True leaves are unmistakable – they have proper, visible veins.
Take a net cup, and drop some growing media such as hydroton in the bottom of the cup. One layer is more than enough. Pick up your seedling still inside the Rockwool or coir you planted it in and place it in the net cup on the hydroton.
Get some more hydroton and fill up the gaps between the Rockwool and the net cup, and drop some more hydroton in until the Rockwool is about covered – but make sure your leaves are still out!
Be careful when dropping the hydroton in as the plants are still extremely fragile and you don’t want to break them.
Fill up your bucket with water up to a level where the last ¾ of an inch to 1 inch of the net cup would be submerged in the water after it’s placed in the hole.
Make a note of how much water you’ve poured since you’ll need that to calculate the amount of nutrient solution to put in.
This will vary from manufacturer to manufacturer so it’s best to read the instructions and see the correct proportions.
If you want to be extra cautious, use a pH meter to make sure the water is slightly acidic – around 6.0 is an ideal range for lettuce, spinach, and greens.
With your bucket containing the solution and your plant in the net cup, it’s time to combine the two. Place the net cup inside the hole you cut out.
Your Kratky setup is now complete. Periodically keep checking the water level to make sure it doesn’t drop too far down.
Plants need some time to grow!
Depending on the nature of the plant, that can be anywhere between a few weeks to a few months to a few years.
If you’re growing simple, small greens, and herbs, you can start reaping the benefits almost immediately within 5 weeks after transplanting or so.
For larger, fruit-bearing plants, it will be a little longer.
While you’re waiting for your plant to mature, just be patient, keep an eye on it, and make sure it’s getting enough light and that the nutrient solution does not run out.
Aside from that, at the end of 4-5 weeks, you’ll have a nice, fresh head of lettuce or a bunch of spinach that you can harvest and enjoy.
Light setup options
If you don’t have access to a very sunny area in your house or on your porch, you’ll need to grow your plants indoors – especially if it’s very cold outside such as in the winter.
That’s the beauty of hydroponics – you can effectively grow all year round as long as you have the temperature and lighting under control.
For artificial lighting, there are LOTS of options.
The cheapest lights that you can get would be T5 fluorescent lights, CFL bulbs, or LED bulbs. LEDs will be the most cost-effective in the long run, but the bulbs are more expensive to buy.
All you need is a holder for the bulbs and some way to adjust the height of the holder.
Ideally, you’ll want to keep the light very close to the plants – about one or two inches above the plant is just right, since artificial lights are nowhere as powerful as natural sunlight.
If you don’t get the lighting correct, the plants will grow long and spindly as they stretch themselves towards the light to get all that they can to photosynthesize and grow properly.
I think the best two options are:
- Use a holder to fit 3-4 T5 tube lights and hang them from a chain
- Use a holder that will reflect most of the LED bulbs light downwards and hang that from a chain
You’ll need some mechanism to adjust the height as your plants grow bigger and bigger, and a simple chain on an S bolt works perfectly.
You can hang the fixture from the bottom of a cabinet, or use some PVC pipes to make a little holder.
What I do is use a little timer socket plugged into the outlet, and the light fixture plugs into the timer. I set my timer for about 16 hours of light per day, so the timer will automatically switch the lights on and off without me having to worry about it.
Once you have a good lighting setup, you can use it for both germinating seeds and for actually growing, too.
There are of course fully featured LED grow lights available too, but those are naturally going to be rather expensive and that would be out of the scope of this post.
The setup discussed so far still does require some accessories like net cups and hydroton. You could technically do away with both using a pool noodle instead, which you can find at a dollar store and cut up into multiple sections.
You cut the pool noodle into cross sections, then snip off a little slice of the cross-section and use it to stuff the center hole.
Then compress the sides from where you cut, and you have a growing media!
If you choose to use this method, you’ll need to make your holes just big enough so you have to slightly squeeze your pool noodle cut-outs and hold them in place with friction.
You’d grow your seedlings in a separate area, and just after they sprout, gently pull them out and place them in the pool noodle, with the roots just touching the water(no nutrient solution yet). As the roots and plant grows, slightly reduce the water level and add nutrient solution, and you’re good to go.
What can you grow in the Kratky system?
Even though the paper was published specifically with a study of varieties of lettuce, you can grow conceivably anything in the Kratky system.
I am guessing the professor chose lettuce for his study because leafy greens are the easiest things to grow.
For truly set and forget plants, I would still stick to greens you don’t need to flower such as:
- Bok choy
- Other herbs
The reason these are set and forget is that you just need a big enough container to house enough water to last the plant through its useful life.
Throughout the course of its growth the plant will take up all the water and nutrients it needs and by the end of it you can harvest the plant, throw out any remaining solution, wash up and start again.
For flowering plants(i.e. plants that produce fruits such as tomatoes, cucumbers, strawberries, etc), things get a little more complicated.
If you’re growing indoors, you’ll need to trigger flowering by:
- varying the light type
- changing the nutrient solution
There are different kinds of nutrient solutions available. Some will be general grow, where the nutrients are those required by the plants to produce leaves and grow.
Other solutions will contain higher concentrations of nutrients required by plants for flowering and blooming. These nutrients are often called “bloom”.
So once your plant has reached a desirable size, and you want it to start flowering and producing fruit, you’ll need to change out the nutrient solution to have a higher proportion of bloom than grow nutrients.
In this manner, it’s not a truly “set and forget” idea – there is going to be a bit of maintenance involved.
Call it modified Kratky.
Also, consider that fruiting plants are generally larger than leafy greens, so again, you’ll need a larger container for changing out the water less often.
Aside from this limitation, I’ve seen people grow just about anything using Kratky.
Indoors or outdoors?
Another question raised is can you use the Kratky system indoors or does it have to be outdoors?
The answer as far as I am aware of is that it can work both ways.
In fact, if the temperature and weather conditions are favorable to the plant, you’ll almost always get better results outdoors than indoors simply because there is a much stronger light source: the sun.
Indoors, you’ll have to provide your own form of sufficient lighting. It’s not hard to do, but if you can harness the sun, why choose artificial light?
One argument in favor of growing indoors is your plants will not be susceptible to pests.
Outdoors, insects, birds, and other animals will come to eat your plants. Indoors, not so much. Things will be much more in control.
You can control the pest problem by growing inside a net covering or greenhouse on your porch or backyard. This way there will still be plenty of sunlight but less direct access to animals.
One argument in favor of growing outdoors – especially if you’re growing fruiting plants – is that nature will pollinate your plants for you. Indoors, you’ll need to pollinate yourself.
However, as far as the Kratky system itself is concerned, indoors or outdoors, both will not be an issue as long as the temperature and light is sufficient.
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