Hydro-conversion, Hydroculture How Toos

These Ficus benjamina trees are growing in expanded clay pebbles (aka hydroculture). The planters are bottom sections of recycled pop bottles. They are what would normally be the reservoir section of the pop bottle planters. They could just as well be housed in any other recycled plastic container. My preference, however, is clear plastic so I can see exactly what is going on. 

With hydroculture, there is no need for a wick and reservoir. The pebbles provide all the structure that is needed. The pebbles are porous and provide good capillary action. There is also enough space between them to create a sufficient supply of water (and oxygen) in the planter. 

Incidentally, these little Ficus trees are in recovery from near death when they were in temporary storage last year. Sometimes it's easier to grow a new plant versus reviving one that has gone through trauma. It can take a long time to recover. These little trees are now on their way to full recovery. I'll post photos of them again somewhere down the road. 

Pop Bottle Planters - In my experience, it works better to use just the recycled pop bottle bottoms when planting in expanded clay pebbles. The neck of the bottle is too narrow to get good wicking action when using pebbles. 

Residual soil or coir on root system – I spend the time to diligently remove all of the soil mix before installing the plant in clay pebbles. The reason is to avoid root rot caused by decaying organic material. I have not tested this to determine if a small amount of residual soil mix will cause a problem down the road. It is yet another test project. 

Replenishment of oxygen – The pebbles being porous will store oxygen when dry and water when wet. Hydroculture is a simple form of hydroponics that does not use an air pump. Oxygen is re-supplied by a simple water replenishment and depletion system. You might think of it as a “rise and fall “ or “ebb and flow” system. 

Preparation of pebbles before planting – There is a significant amount of pebble dust in a bag of pebbles. It is a good idea to wash and drain them several times before planting. Use a colander or strainer for smaller quantities. 

Adding water in a commercially available hydroculture planter – Commercially available hydroculture planters have a water level indicator with a float that shows the status of the water level (i.e. full, empty). Add water until the floating indicator shows full. Add water when indicated by the float. 

Adding water on a fixed schedule using a homemade pipette tube – Although you will find widespread advice to the contrary, I water on a fixed schedule. Because of many small plants with limited container capacity, it is currently every 7 days. 

Most of us do not have time or motivation to be daily plant nannies. I have been maintaining plants on a fixed schedule both professionally and as an avocation for over 30 years. It works! 

Once you gain some experience with this method you can use if for any size planter. This explanation will apply to the small size planters in the photo. 

Start with no water in the container. The pebbles, however, should be moist.  

Estimate how much water you think the plant will use in a week. For this small planter, lets add 7 ounces of water. Make a note of the amount of water added. Observe the water level go down using the pipette or observe through the clear wall of the planter. The pipette is the most accurate method. 

When the water level goes down to empty (as confirmed with the pipette) you can easily calculate the water used per day. This water consumption rate is primarily a function of the light level, plant species and plant size. 

Once you know the daily water consumption, you can add enough water to last 1, 2 or 3 weeks if there is enough planter capacity. With small planters like these, it will be more like 7 to 14 days at the most. 

You will find that over time the plants will use more, or less water due to varying amounts of light due to weather or seasonal change. Simply adjust the amount of water added (up or down) based on the water consumption during the prior period. 

Residual water – a safety margin – Even after the pipette indicates the planter is empty; there is about 3 days worth of moisture in the pebbles. 

Plant is not using water, or a very small amount - Note that if the plant is not using water, the light is too low. The plant is now communicating with you. It’s all about light and water relationships. This is the key to maintaining healthy plants. 

Comments

[Tarek]

Bob, this is fantastic info, thanks so much!

One last question - do the ficus need additional nutrients once they're in the pebbles?

[Greenscaper]

Oops! Good catch Tarek. I'll update the post to include the fact that I use a constant feed method. In hydroponics they don't talk about water, it's the "nutrient solution". I've been using Dyna-gro Foliage and Dyna-gro Bloom for many years at an application rate of 1/2 teaspoon/gallon. I use this for plants in soil mix also.

[anomynous]

Thanks for the info. It's funny, when I went to a hydroponics store near me to buy Hydrotron, I was told that they would never work for this purpose as they are not porous enough and the clay would dry out way too fast. Do you suppose they were just saying that because they grow everything under HID lighting?

[Greenscaper Bob]

In my experience hydroponics retailers no little about these methods (or maybe don't want to know about them). Their objective is to sell equipment! Unfortunately, they are more interested in talking to you if they know you are growing marijuana rather than vegetables. It will take a while but an item like clay pebbles will become mainstream and available at retailers other than hydroponics stores.

[Nisha]

Hello,
I discovered your blog by chance and have been fascinated - hydroponics, hydroculture, SIPs - this is all new to me but you have made me a believer and I can't wait to get started! I had a few questions though: does hydroculture work for outdoor plants or is this primarily an indoor plants methodology?
do you have any tips on converting existing standard containers in my patio (the ones I have are the plastic terra-cotta lookalikes commonly available in Home depot etc)to the Sub irrigation system? I have tried to piece it together from your blog but am still a little confused.
thanks for your help and your writing.. keep up and good luck!

[littlefish]

nisha, i've done this exact thing using bob's SIP method. key is to find a watertight container that can fit under your plastic pot to act as a reservoir. you can use another same size plastic pot for this purpose if you can make it watertight (try styrofoam pellets and 100% silicone caulk to fill the drainage holes). then put something in the bottom 1/2 of the watertight bottom pot (e.g. a layer of clean gravel for instance) to raise the inside pot and provide a reservoir underneath. then, string a wick through the drainage holes of the inside pot, put the wicked pot inside the watertight pot and voila.

-make sure that the wick is buried in the gravel and does not lie on top of the layer.
- drill a hole or 2 about 2/3 of the way up the watertight container to act as an excess water drain and air hole.

[Peter Kesel]

Good cultural story. I read & appreciate it.

[Esljobsworld]

Woah thanks for the information especially on how to calculate the water levels.