The Kratky method: A Passive Hydroponic way to grow plants

If you want to try to get a bit of hydroponic growing happening but don’t know where to start, then the Kratky method is for you. It’s the sort of passive hydroponics that are an excellent starting point for beginners. It’s also an easy, “set and forget” technique that veterans can use to squeeze a bit more out of every forgotten corner. It’s the easiest of all the Deep Water Culture techniques, hands down. All you need is a bucket with a hole in the lid, a sunny spot and bit of patience.

Kratky method of growing herbs
Kratky method of growing herbs

What is the Kratky Method?

The Kratky method is a simplified way of growing plants hydroponically. The process involves placing your plants in jars or containers with a nutrient dense solution of water without the use of water pumps and aeration. The plants are suspended above the water and are sealed off from open air to allow for root growth that reaches towards the water below.

The Kratky Method was developed by University of Hawaii researcher Bernard Kratky as a self-contained system. He and his colleagues experimented with cucumber plants grown in plastic trash bins in 2000 before moving on to lettuces in 2009.

It’s elegant in its simplicity. Plants in hydro need nutrient solution at their roots but they also need to breath. Most active systems supply that air with machines of one kind or another.

In this method however the plants themselves provide their oxygen in a roundabout way. Plants are placed in a sealed container of nutrient solution with their roots more or less dangling below. As the plant shoots up it uses the water in the reserve and gradually exposes the roots, allowing them a perfect balance of water and oxygen. By the time the reserve is dry it’s ready for harvest.

“Homegrown lettuce in the dead of winter or the heat of late summer? It’s possible with hydroponics. And you don’t need a fancy setup with electric pumps and a water circulation system. The Kratky method lets you do it with a grow light and an empty coffee bin. “

Robert Cook, University of Maryland Extension Master Gardener

Which types of plants grow well in Kratky hydroponics?

Lettuce

Lettuce is a perfect starter crop for those new to hydroponic gardening. It was after all one of the crops used to develop this low-maintenance technique. I’ve seen great little units build in re-used coffee containers or the like. Compact varieties are ideal to put in a small container and allow you to get the most from your growing space.

Discover  How Long Do You Soak Air Plants? A Complete Watering Guide

Basil

There’s no such thing as too much basil. You can grow kratky basil in a rig made from as little as Mason jar on a kitchen counter. I’ve even struck root off store bough basil bunches to get started. They’re unbelievably vigorous plants and delicious too.

Cucumber

If you’ve got a lot more room to play with cucumber is a great choice. They want larger containers and space to spread. Those glorious vines will also need a trellis or other support. But once they’re off and running they’ll continue to provide delicious crisp fruit with no need for extra fertilizer along the way.

Cabbage

Like lettuce cabbages thrive under the Kratky method of hydroponic cultivation. They’re good candidates for sequential plantings a few weeks apart, and growing indoors is a great way to keep them pest free too.

Peppers

I generally don’t recommend you use the Kratky method to grow heavy feeders like tomatoes and peppers. It’s just too easy to under-nourish during the critical flowering phase if you’ve locked their water and nutrient solution inside a big box.

But I make exception for peppers. If you’re gunning for truly fiery, fruity peppers you can control inputs best if you grow the plants with the Kratky method. Keeping each set of roots in its own closed environment means you can supply the right amount of nutrients to please each plant without neglecting the others.

What are the benefits of using the Kratky system?

Kratky Pothos
Kratky Pathos

Flexible

The uses for this sort of passive system is only limited by your imagination. Just about any closed container can hold plant food. Small rigs, large ones, single crop or salad tables all work off the same principle. It’s such an easy way to grow it’ll adapt to almost all situations. No matter what you want to grow there’s a way to make Kratky work for you.

Cheap

If you’re new to hydroponics the cost of startup can be daunting. While I love my Aerogarden not everyone can afford such a sophisticated system. But everyone has a right to fresh food and Kratky hydroponics are easy to set up with very little investment.

If you have access to good light, rainwater, an old tub and some plant cuttings you can grow plants with the Kratky method. There’s no running costs for pumps and filters. Once you’ve added a nutrient solution you’re essentially done. About the only real investment an electrical conductivity meter and they are increasingly affordable online.

Environmentally Friendly

Kratky is a supremely environmentally friendly type of hydroponic system. Recycled containers hold hydroponic nutrient solutions just as well as purpose made. Baskets and substrate like clay pellets can be reused time and time again. I’ve even heard of people cutting slits in Dixie cups for baskets too! It’s thrifty and puts trash to good use.

The environmental benefits don’t end there. Because the water solution is sealed it limits evaporation and saves a lot of water from waste. You only need to water once all season. Even drip irrigation systems will go through more than that.

Discover  What Should the Roots of a Healthy Snake Plant Look Like?

Lastly if you’re lucky enough to have a well lit spot you don’t have to power anything at all. Even here in the Great White North I can cut my energy input down to a high efficiency LED grow light.

How to set up a Kratky Hydroponic System:

You will need:

  • Plastic container or tub with lid.
  • Mesh basket
  • Growing medium
  • Nutrient solution
  • Water
  • Seedling or rooted cutting
  • EC/pH meter (optional)

Step One

Start by preparing your medium. If you’ve opted to use clay pellets, soak in clean water overnight. Rinse coir to clear any extra salts.

While your medium is soaking prepare your container. Opaque containers are best as they prevent algae in the roots. Wash and rinse thoroughly and allow to dry.

Cut a hole in your lid. It must be cut to fit your basket so that it sits firmly but allows it to hang comfortably below.

Step Two

Once your medium is ready to go, mix up your solution.

For beginners, a commercial nutrient solution blends designed for leafy greens is good. Always mix the nutrients according to instructions. Tap water is generally fine but if you’re concerned distilled water is okay too.

Just be sure to follow the instructions. The specific amount of water listed on the label should give you a good pH and the right nutrient concentration.

If you want to use a more general purpose liquid fertilizer check the pH and electrical conductivity before you add plants. An electric EC and pH meter won’t be hard to find online and they’ll help you keep a close eye on any future hydro experiments too.

Once the solution is prepared fill the container leaving the depth of the basket clear at the top, and pop the lid in place.

Step Three

Plant your seedling in the moist medium. Ensure the roots are well distributed inside.

Step Four

Place your basket in the lid so the bottom is just touching the solution. At most it should not be submerged no more than a quarter of an inch.

Step Five

Place your newly built Kratky rig in a well lit area. If you’ve opted to grow away from natural light position your grow light too.

What is the Best Growing Medium for the Kratky method?

I love clay pebbles for Kratky rigs. They provide great support to plants and keep them both hydrated and well aerated. Clay pebbles don’t rot and drop debris into your tank. Once you harvest your vegetables you can wash and reuse them for the next round too. There’s a lot to recommend them!

That said clay pebbles can be a bit expensive in some areas. Coco coir or perlite work well too.

Vine of pathos growing from a kratky jar
Vine of pathos growing from a Kratky jar

What are the disadvantages of the Kratky hydroponic method?

Limits to size

While Kratky is a flexible method, you do have a hard upper limit for size. It really isn’t practical to try and manage huge tubs of water. My back is sore just thinking about it. Not to mention the hazards of having that kind of weight on structures like decks or balconies. Ebb and flow or drip irrigation is better for truly expansive systems.

Discover  How to Choose the Best Soil and Container for Your Money Tree

Limits to time frame

Kratky is best for shorter lifespan crops that are harvested at the end of the growing season. Long-lived types of plants will drop the water level in the reservoir down to nothing over the course of their lives. Crops like hydroponic blueberries are going to run out of water or nutrients long before they’re ready to harvest.

Root Problems

A closed dark tub filled with motionless water and nutrients is a paradise to root diseases like Pythium and Phytopthora . While there’s no greater risk of disease in simple hydroponic rigs like these it does make it far harder to spot and treat root problems.

Can I Top Up My Kratky Nutrient Solution?

It’s perfectly fine to refill your reservoir if your plant empties it before the growing season is done.

Warm weather makes for thirsty plants that substantially drop the water level in the tank. You may also have just misjudged how much you needed or wound up with a real grower of a plant stripping the nutrient level.

If you do refill you need to be aware of the oxygen needs of the root system. You can’t just fill the reservoir to the top as you did at the start. Aim to cover about half of the total root mass. This will keep the nutrient level just right while providing roots the air they need to thrive.

You also need to really check the EC and PH. High temperatures can also cause your solution to become too concentrated. It pays to test before you close that lid again.

Is Kratky similar to Deep Water Culture (DWC)?

Kratky is indeed a Deep Water Culture hydroponic method. Generally when folks talk about Deep Water Culture they mean more complex builds with filtration and aeration systems. These are ‘active’ hydroponic systems.

Kratky setups are a passive hydroponic system. Also called non-circulating hydroponic systems, they don’t require pumps, filters or air stones. The simple system exploits the way plants exhale water taken from the roots into the air. As the water level drops it provides oxygen to the root zone that only increases as the entire plant gets larger.

Final thoughts

I love a completely passive system and the Kratky is the easiest to set up and use. It provides everything that my plants will need over their lifespan right at the start. Once they’re going I don’t need to check much at all and I can leave them alone until they’re ready to harvest. It’s “set and forget” at its finest. I’ve had great success with leafy greens and might just branch out into trickier crops like hydroponic strawberries. Experimenting is half the fun even with the most basic hydroponic techniques.

Brock

Brock is the head gardener and writer behind Bigger Garden. Every year you can expect to see something new in his raised beds, from purple broccoli to cotton candy peppers.

Recent Posts