Brief evaluation of this year’s tomato Kratky experiment

An update after a long pause. I received a few questions asking me about the progress of my Kratky experiment, and want to apologize for having taken so long to respond.

So here it is in a nuthsell: Despite the mysterious leaf disease, the Kratky tomatoes (grown inside) finally did produce a crop in July. In Late August, when even the last tomatos ripened, I’ve taken the Kratky set-up down till the next growing season. Overall, the experiment was successful and I intend to try it again.


The positives: The tomatos in the Kratky set-up ripened significantly faster than those left in soil on the terrace. In fact some of the tomatos grown conventionally outside have not been harvested till the time of writing this post i.e. October. That is largely due to the fact that I live in a climate which is relatively cold with lots of rain, not ideal for growing tomatos outside. So behind windows with good sun exposure (south-east in my case), one can get fruit with the Kratky method very quickly. In colder periods, I added/changed water about once in two weeks, in the hot spells as the tomatos were ripening, they were able to drink up the whole 8l container in a week! Even that is comfortable compared to the outside soil containers, that needed watering every day.


The negatives: In the end, I haven’t found out what exactly was the cause of the leaf spots. However, I suspect it was some sort of a fungal disease, possible aggravated by lack of air circulation and damp air inside my flat. The plants outside ripened slowly, but suffered no leaf disease at all. Also, the outside plants produced more fruit, probably because of better pollination thanks to wind and insect pollinators, both lacking inside behind the window.

I’ll conclude this post with a photo of a few tomatos from this year’s Kratky experiment (the greens are from the terrace).


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Kratky method update: tomatoes have survived their first disease (at least for now)

Just returned to base after several weeks of absence and checked my Kratky inspired non-circulating tomato system. The first photo on the right shows how the system looked before I left.Image

There were several legitimate reasons to be worried. A few days before departure, I discovered strangely discoloured spots on the leaves (see below). ImageThen, most worryingly, I found out that the roots lost most of their finest hairs, and instead were covered in slime, seemingly dissolving into the water, in the process creating an ugly looking whitish film on the surface. In other words, it seemed the roots are slowly dying, and possibly are already beyond repair.

From a quick online search, it seemed the tomatoes suffer from a bacterial infection of the roots. However, I couldn’t exclude the possibility that somehow, the growing method itself is at fault, not providing the plants with enough oxygen (as it is a passive system with no water movement).

As first aid, I discarded one plant that was affected the most, changed the whole nutrient solution, and cut off all the diseased leaves. Even so, I was resigned to finding the plants dead (or close) upon my return two weeks later.

Fortunately, it turns out that the change of water and drastic pruning helped – at least for now. Yesterday I have found the plants not just alive, but healthier, and bigger than before, plus starting to flower. The roots have mysteriously recovered, and re-grown, and almost all the water in the container was consumed or evaporated during the heat-wave (only about 3cm were left at the bottom), requiring an immediate re-fill. Image

As is apparent from the photo taken a moment ago, the tomato plants are attached (using strings) to an improvised support system built from IVAR Ikea elements, and a few horizontal straight wooden sticks. I also acquired a small and cheap USB ventilator to keep the plants cooler during hot days and to make sure the flowers move in the breeze (without movement, they might not pollinate and bear fruit).

So it seems that so far so good, but I don’t think I’m out of the woods completely. A few leaves are still sick, the infection can return at any time, and I don’t know how the plants will react to the nutrient solution re-fill, due to which roots previously out of the water will be immersed again. Since I’m not sure what caused the problem in the first place, I’m equally in the dark about preventing its return in the future.

So while I’m prepared for the worst, I’m still hoping for the best.

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Keeping it simple: Salad grown using non-circulation hydroponics (aka the Kratky method)

I used to think that hydroponics needs a lot of hardware, such as tubes, air-stones, multiple containers, and the like, and of course electricity to power the pumps moving water or air or both. To my delight, it turns none of this is strictly necessary. In fact the only thing you need to grow certain plants, including salad greens, is water, nutrients, support for the plant, and most importantly for this non-circulation method, a space filled with damp air between the water-level and the container cover, from where hanging roots can absorb oxygen. If the plants’ roots were completely submerged in water, chances are growth would be limited, the plant would be weak, and might even die altogether, effectively ‘drowning’.

This particular set-up consists of a single 11 liter  Samla box from Ikea with a corresponding lid (less than 2 EUR altogether), into which I drilled 5 holes to house 5cm net-cups (see photos). I used the remaining bits of plastic cut out from the lid (as well as a few yogurt bottle lids) to block light from reaching the surface of the substrate to prevent algae growth (the algii like to ‘steal’ nutrients from the crops). As fertilizer, I use the GHE Flora Series hydroponic nutrients, which consists of MICRO, GRO and BLOOM elements, out of which I only use the first two, since flowering or fruiting is neither required, nor desired in salad greens, unless you want to collect seeds for next season).

Then I re-planted small seedlings with a single set of leaves into 4cm rockwool cubes. In turn, I placed the rockwool cubes into the net-cups, with about half of the cups submerged in the nutrient solution. Unlike in my previous experiments, this time the size of the container (11l) should be sufficient to ensure that no further adding of water or nutrients will be necessary (over 2l per plant should be enough, especially in this year’s cold weather). As the water level drops and the air-pocket gets bigger, roots grow longer, thus still reaching into the water-nutrient solution.


About a week after the first plants, I added a slightly older  Crebiata Catalogne salad plant (previously kept in the tomato container) to the same set-up. This wasn’t the wisest thing to do, since ideally, all plants in a Kratky system should be of roughly equal size and age to let them compete for ‘resources’ in a level playing field. Otherwise the strongest plant usually establishes the strongest roots and over-grows the others. In my case, this ‘alpha’ plant was the newly re-planted Crebiata Catalogne (in the centre) , which already had a strong root-ball at the moment it was introduced among the smaller and weaker seedlings.


Notwithstanding, about 3 weeks later, the whole ‘salad plot’ looks almost ready for the first harvest:


Next time, I will try to plant everything at once, and stick to placing a single variety (or very similar varieties) into the same space.

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Avocados are easy to grow from seed using this simple method. Just arm yourself with lots of patience.

The fact that avocado is easy to grow from seed is well known and sufficiently documented online, but I still couldn’t resist adding my own version. To suspend the seed so that it’s bottom touches water, most people use toothpicks, while I opted for a pair of unused gift miniature party forks that I frankly didn’t know what to do with.







After what seemed like forever (about 3 months), the avocado on the right suddenly came to life, it split in two, and sprouted two roots and a little green shoot (see photo on the right). If it survives, I might later re-plant it into a regular pot and give it as a present to a friend.

Although the seedling probably uses nutrients stored in the seed, I’ve added a tiny amount of hydroponic nutrient into the water to make it grow faster.

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Hydroponic Tomatoes grown using the Kratky Method in a plastic balcony container

About three weeks ago, I started a few tomato seeds, and a single salad seed on a damp paper tissue. A couple of days after sprouting, I re-planted them into a non-circulation hydroponic set-up based on the principles described by Professor Kratky from the University of Hawaii, often referred to as the Kratky Method.


The set-up consists of an 80cm balcony planter without holes (the kind where you’re supposed to drill drainage holes yourself if you want to use them for soil gardening) filled with nutrient solution. As top cover, I used 2 half length (40cm) trays meant to be put under 40cm planters of the same type. The trays are a few milimeters longer than the planter, so for perfect fit, they needed to be shortened by s few milimetres with a saw.


Openings of 5cm in diameter were cut-out in the trays to house 6 net-pods with rock-wool and the plants. At the start, about half of the net-pods should be immersed in water. Later, water level drops as roots get bigger.

While making the holes, the trays cracked in a few places, so the result is not very aesthetic, but the whole thing still holds together. When filled with water, the container becomes a bit wider due to the pressure of water against the sides, which is why I tied a nylon string around the center of the pot. Overall, there are about 2 litres of water-nutrient per plant.

So far, the tomatoes have been doing really well in the this set-up, being at least twice as big as plants from the same batch (sprouted at the same time) that I placed into soil on the balcony (left image below).

Potential problems and obstacles I see in the near future

Two liters of nutrient solution per plant is probably not enough to bring tomatoes to fruit without re-filling, so some topping-up will be necessary. Another challenge I’ll soon have to face will be providing a trellis the tomatoes can climb on. Further, I am not sure if the space left for roots in the hydroponic set-up is big enough for six plant in an 80cm pot.


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Thai basilic thrives in a non-circulation hydroponic set-up, shown side-by-side with a soil-grown specimen

This side-by-side comparison of a soil-grown and hydroponically grown basil isn’t meant to be a proof that hydroponics always gives better results than growing in soil. The pot with the soil-grown plant (the one on the right) is simply too small to offer ideal growing conditions, which makes the comparison unfair.

However, the sheer difference (notice the huge leaves of the hydroponically grown basil) between the two plants is striking, especially taking into consideration that the hydroponic plant was started as a cutting from the plant on the right, although now, they’ve come to look almost as two different varieties.


At the very least, it suggests that it is possible to grow a healthy looking plant without soil, i.e. hydroponically, but also that one can do so without any pipes, pumps, electricity, moving water, aeration or other features considered indispensable by many hydroponic growers.

In fact, the only requirements are: a non-transparent vessel (to prevent the growth of algi) filled with a full hydroponic nutrient solution, a net-cup with a non-soil substrate such as rockwool, and a gradually forming humid-air space between the bottom of the net-cup and the water-nutrient surface allowing air-exposed roots to absorb oxygen.

Maintenance is needed only if and when nutrient solution risks evaporating almost completely before the plant is harvested.  In other words, the bigger the vessel and the shorter the life-span of the plant, the less maintenance we need.

In this case, since the thai basil is grown in a glass of merely 500ml, topping up nutrient (or replacing the whole solution) once every few weeks is unavoidable.

With bigger containers though, this problem can be reduced to minimum. I’m not saying that every plant can be successfully grown using this ultra-simple non-circulation method, but thai basilic certainly can.


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Outrageous VHS tape planters

Yes. That’s correct. I really mean those prehistoric clunky VHS video tapes. Walking along an otherwise unremarkable busy street today, I suddenly spotted these wonderfully quirky planters made entirely from old video tapes glued together. Not exactly my aesthetic style, but I appreciate the intent of transforming something old and relatively useless into a new object, especially when it’s used to grow plants!Image

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