Are you ready for a little visualization experiment? Close your eyes… and imagine a hydroponic garden… What do you see? Maybe you see grow tanks, pipes, but what about the planting? Which plants did you visualize? Were they strawberries? Lettuce? Tomatoes?
I bet that you saw lots of plants, lots of green leaves… But I also bet that you did not see any big trees, did you? What we picture when we talk about hydroponic gardens are small plants in most cases.
Why is it so? Maybe because we believe, or rather assume that tees cannot be grown hydroponically.
In fact, when we imagine where our apples and pears come from, we always think about a fruit garden under a blue sky. But is it really true that trees cannot grow in a hydroponic garden?
Can Trees Grow In Hydroponic Gardens?
The straightforward answer is yes. But… Not all trees are easy to grow hydroponically. Shall we see why?
These are mainly technical problems… “But is there a botanical obstacle as well,” you may ask? Just bear with me…
Hydroponic Trees – The Big Problem: The Roots
If you want to understand why big trees are just not suitable for hydroponic gardening, you need to understand how roots work.
Roots can have a primary growth and a secondary growth. The primary growth is the phase when roots grow in length.
But there is an issue with secondary growth in many large plants; this is when roots thicken, and in this process, especially big perennials go through a transformation of the outer layer of the roots called “cork cambium”.
And cork cambium is our problem; this is the formation of a hard layer in the periderm (the outer “skin” of roots, stems and so forth).
This is an excellent defense for the plant against the weather, too much heat, even humidity. But, unfortunately, if it is immersed in water all the time, it may rot.
In simple words, it’s like putting a tree trunk in water.
The Solution To The Big Problem
Is there a hydroponic solution to this natural obstacle to growing trees hydroponically? Well, more than a full blown solution, there is a choice: some hydroponic systems and techniques are not suitable for trees.
The good news, though, is that some hydroponic systems and techniques are better suited for trees.
I can hear your question now: “Which hydroponic systems are good for trees?” I am sorry but you will have to wait a short while for the answer.
Let’s get our priorities straight; first the real protagonists, the trees, then the best hydroponic methods to grow them…
Which Trees Are Not Suitable For Hydroponic Gardening?
Isn’t it better to know which trees you cannot grow hydroponically before you jump ahead with your plans? Of course it is, and you cannot grow a large size adult tree hydroponically.
Think about it, this excludes the vast majority of trees; no big cherry blossoms in spring in your hydroponic garden, I’m sorry.
Nor will you have a hydroponic fir tree in your garden as a “novelty feature or item”, I’m afraid.
In fact, the same root growth we talked about before posits an insurmountable problem: the secondary growth roots will literally strangle the primary growth roots.
When they thicken, they just squeeze the other roots, preventing them from growing, and from finding water and nutrients.
How Large Can A Hydroponic Tree Be?
The biggest hydroponic trees you can see around the world hardly reach 10 to 15 feet tall.
That may seem a lot at first glance, but for a tree, it means being on the short side. And this includes fast growing trees like papayas.
The largest decorative tree grown hydroponically is allegedly a Ficus in Chico, a town not far from Sacramento in California. This tree is 30 years old as we speak and its branches are about 13 feet wide.
Which Trees Can Be Grown Hydroponically?
No oaks, no pine trees and no baobabs then… So, which trees can you grow in your hydroponic garden?
The list is growing, as more and more people experiment with new species, and there are even reports of baby redwood trees being grown hydroponically.
In any case, I think you will be surprised. Here are the best possible trees to grow in a hydroponic system:
Hydroponic Dwarf Trees
You will be surprised at the inventiveness of hydroponic gardeners and growers – and at their stubbornness too; faced with the compelling desire to grow everything with their favorite gardening method, and faced with the problem of size, many have taken to growing dwarf varieties to prove that everything is possible.
And to a fair extent, they are succeeding…
Dwarf fruit trees have a high yield for their size, and they have turned out to be a valid alternative to large trees indeed.
You won’t be feasting on cherries for a whole season, but you can still put them on your table.
How Successful Is Hydroponic Tree-Growing?
So far, if we compare the great success of hydroponics with fruit vegetables, leaf vegetables and even root vegetable that at first were a pretty harsh problem to solve, growing trees has not fared as well.
On the whole, if we were theater or movie critics, we would say that hydroponic tree growing has received “mixed reviews” – and maybe this is the best description of the current picture.
While there are enthusiasts who keep experimenting and notching up small successes, the general consensus is that this has not been, on the whole, a very successful story.
But we never know… Remember, as we said, long ago (or so it seems) even root vegetables, especially deep root ones, were thought of as “not suitable for hydroponics”, and this field is very innovative by nature and growing fast.
Which Hydroponic Systems Are Not Good For Trees?
I know, I kept you waiting, but here we are finally! Let’s start with hydroponic systems that, as a rule of thumb, are not suitable for trees.
The Kratky Method
The most basic hydroponic system is the Kratky method; it simply consists of a vessel capable of keeping the areal part of the plant above water while its roots grow in the nutrient solution.
Sure you must have seen sweet potatoes growing out of jugs and vases… That method!
Needless to say, a tree will not fit in a jug, but even if you had a big, massive vessel, there would still be the problem with the woody roots that we have already seen.
Having said this, some people do use this simple method for growing saplings of bigger trees. I haven’t seen anyone successfully grow a whole adult tree with the Kratky method yet though.
The Deep Water Culture (DWC) System
This hydroponic method, where the roots are constantly in water (with or without a growing medium like expanded clay) is a “classic” method, but for hydroponic growers (or “gardeners” as I still like to call them) it often is a bit like an “oldie”.
It’s no longer used as much as it used to but it brings back memories…
For the same reasons as before, deep water culture is not really good for trees.
What is more, you need an air pump to oxygenate the water, and it is quite hard to have homogeneous oxygenation when the root system is very developed.
Just imagine trying to get the air to the central roots bypassing all the other ones. And remember that there’s the problem with the density of the roots with hydroponic trees already.
The Wick System
This is slightly more suitable than DWC. Why? Put simply, because the nutrient solution travels through what is known as “capillary action” (a bit like in a sponge) from the reservoir (or sump tank) to the grow tank where you have a grow medium, there is a more limited amount of nutrient solution in the grow tank at any time.
Basically, the plant “sucks” the nutrient solution from the reservoir through the wicks, a bit like you do with a straw when you drink a cocktail on a beach.
Here too, however, there is another problem… The reservoir usually goes under the grow tank for practical reasons: you want the excess nutrient solution to escape through a hole back into the reservoir.
And here’s the rub… You would need to grow a big tree in a big grow tank on top of the sump tank itself… I can see you scratching your head…
A Promising System
There is a fairly recent study that shows that even the nutrient film technique (if you are an acronym lover, “NFT” for you) can be used for trees successfully.
This was done in Trinidad with research from the University of West Indies; they tested NFT on a whole garden (25 x 60 feet in size) with many plants, including trees and, apparently, it worked.
But I see some problems here… To start with, the experiment was meant to look at overall production with mixed garden.
Second, they had a large structure. Third, I still find that the nutrient film technique has a problem with the root system of trees.
Why? The NFT is a system where you have a thin film of nutrient solution flowing down a gently sloping tray.
This way, only the very bottom of your grow tank has the nutrient solution. For small plants, this is fine, because they will push the roots down to the nutrient film and then grow horizontally along it. They end up looking a bit like mops in the end.
But think about a root system with large, woody roots and then younger roots spreading from them. How would that adapt to this type of growth?
And how could you do this on a small-scale garden?
Which Hydroponic Systems Are Good For Growing Trees?
Three down, one floating – sorry about the pun… Let us see the ones that do work now!
Did I tell you this is a chart, like the Billboard Hot 100, and we have now reached the top 3? So, who’s on the podium?
Ebb And Flow System
This is a system where you have a water pump that fills your grow tank with nutrient solution for short periods of time (up to 15 minutes) several times a day, and on some occasions also once or twice at night – if it’s hot and dry for example.
Then, the pump reverses and it sucks the nutrient solution up to send it back into the reservoir.
Excellent for many reasons (aeration, good humidity levels, no stagnation of the nutrient solution etc.). It is actually a favorite with deep root vegetable growers. And it has been found to work also with trees.
However, this system has some disadvantages:
Still, don’t lose hope; we are getting to two systems you can fully trust now…
Finally, we get to a system you can use safely; tried and tested with plants and trees alike, the Drip System is so far the best so far for growing trees.
In case you don’t know how it works, have you ever seen water pipes stretching out in crop fields? It is virtually the same, only the pipes drip (with a simple hole or nozzle) on plants that live in grow trays with a growing medium (expanded clay etc.) that makes sure that:
As you can see, this system allows you to send little but constant quantities to your tree and then, thanks to the capillary action of the growing medium, it will reach all the root system and stay inside the medium there to be absorbed when the tree needs it.
At the same time, it will keep your tree’s “feet” comparatively dry.
“Hold on,” you are thinking, “is this not a top three? You’ve only given us two methods!” Trust me, I have not cheated… The best one is still to come…
And The Winner Is… The Best Hydroponic System For Trees…
Ok, I’ve been cruel enough today… But I can’t keep you waiting any longer. The winner of the all-time best hydroponic system for trees is… (suspense): the Dutch bucket system!
You may not find this method in most books and articles, but in my opinion, if you want to grow trees hydroponically, there is no better way to go than… go Dutch! Ok, humor aside, what is this fabulous system?
It is a drip system, but instead of growing your plants together in a grow tray or tank, you grow them individually in big black (to prevent algae growth) bins. They look like black plastic buckets, or like those bins farmers use to store water.
Only, they have a hole at the top for the trunk to grow out of, they are filled with a growing medium and there’s a pipe that brings the nutrient solution to them.
Simple And Effective, This System Has Major Advantages:
Some Tips For Growing Trees Hydroponically
Award ceremony over, let’s see some practical tips for growing trees hydroponically. You may be concerned with light, ventilation, pH, humidity etc. – and rightfully so.
These are all things you need to plan carefully if you want to grow healthy and happy trees. Plants do respond to your attention, you know?
Not all trees need the same light of course; figs will need a lot, while I have seen orange trees and papaya trees grow as bottom top layers in food forests.
So, make sure that especially if you want to grow a tree that loves the Sun, you place it where it gets it.
You can grow trees hydroponically outdoors, on balconies, terraces and even in gardens if you want – and can… But how about if you want a small tree in your home or even in your garage?
Get some LED grow lights then. If light is not enough, the fruits simply will not ripen. For a tree, I would suggest avoiding tube lights; they heat up the tree, the light is not uniform, they don’t have a timer… They even use a lot of electricity.
Get good LED grow lights with a timer and you will save on bills, give your plants the right light, for the right time and without risking that you burn the leaves. And… You just need to plug them in and set the timer.
The opposite is true too; not all trees like extremely strong, greenhouse light conditions; figs will bathe in it and thank you, but cherries, apples and pears will end up with sunburn.
So, use some shading nets if this is the case, especially in summer.
Most trees have their leafy “heads”, the canopy, in the wind. That makes them different from plants that grow in the underbrush. They like to feel the breeze, they need it to be healthy.
So, always provide excellent ventilation for hydroponic trees, or you will start with a series of problems like molds, mildew, parasites etc.
Keep in mind that hydroponic gardening very much depends on the acidity of the nutrient solution.
It even affects the EC (electric conductivity) which you use to measure if the nutrient solution needs changing…
The pH for hydroponic trees should be between 5.5 and 6.5 (some say 6.8) with an optimal pH of 6.3.
Keep a close eye on this, because the pH also affects how fast your plants will absorb the different nutrients; each nutrient changes the speed of absorption according to it; some enter faster into the roots with a low pH, other with a high one.
And you don’t want to give your trees an imbalanced “diet”, do you?
Not all trees like the same pH levels though:
So, if you have many different trees fed from the same sump tank, your best option is to check the pH daily and keep it between 6.0 and 6.5. I know, it’s a small margin.
In most cases, though, if you have just one type of trees, you have much more room for maneuver.
This goes a bit with ventilation but it does not necessarily coincide. Most plants want humidity that is between 50% and 60%.
Trees that come from dry regions (figs, bananas etc.) will stand lower humidity rates; those that come from rain forests will stand higher rates on the other hand.
In any case, careful if you grow them indoors; high or low levels of humidity are usually tolerable to plants outdoors for short periods of time, but indoors, they usually spell disease or sickness.
No Tree Is An Island
Sorry to have misquoted John Donne, but with the water theme… I just couldn’t resist! We have seen how despite what people believe, there actually are trees you can grow hydroponically.
True, not all trees will be happy as little islands in your “floating garden”, and not all floating gardens will be welcome homes for your trees.
Choose wisely and, if it looks ironic that I suggest that you use a Dutch bucket system and then say that “no tree is an island,” maybe it is not: even in a small individual home like this, plans like to keep company with others around them, trees especially…
And finally, always keep in mind that if you choose to grow a plant or tree hydroponically, well, it falls to you to be its best friend!
After many years as an academic in London, Adriano Bulla became a writer, publishing books like A History of Gardening, Organic Gardening and Elements of Garden Design; he then decided to become a gardener, following his childhood dream, and has been following his dream writing and gardening professionally in Southern Europe, where he has specialized in new and innovative organic gardening fields and techniques, like permaculture, regenerative agriculture, food forests and hydroponics.