EC and Potting Soil

[Alex]

Hi,

I would like to know what the correct EC is for the potting soil of various plants.

Is there any website that has this information?

Thanks

[David E. Ross]

What is "EC"?

[David Hare-Scott]

Electrical Conductivity. Used as a measure of dissolved salts.

David

[Alex]

Right. Most descriptions for plants say 'use a light mix' or something like that - I want to be precise and know exactly what my plants are going to need, and what they're getting, which is why I measure runoff with an EC meter.

However, it is difficult to find the correct EC (or ppm/parts per millions) for plants online.

So I am wondering if someone has come a across a website or a book which gives you good information over what to use.

Alex

[David Hare-Scott]

I don't think this will work.

I don't think this will help much, if at all.

I am not sure that there is a "correct" EC for each plant. A given EC is the result of the agregate of the dissolved salts in the sample but depending on the combination of cations and anions that make it up it could be suitable or unsuitable for a growing medium. For example an EC of "X" might be made up of a good balance of salts supplying all the major and minor elements or the result of just sodium chloride. Also the presence of certain quantities of soluble minerals is not a good indication of solid medium fertility as some quite adequate nutrients may be available as partly soluble compounds which contribute little to the EC reading. Likewise an EC in the "correct" range will not tell you if some trace elements are missing.

My understanding is that EC is used to estimate when excessive salts might be present. The higher the EC the fewer types of plants that will grow in it assuming that the correct elements are present. Thus it can assist in saying if medium is unsuitable (the EC is too high for the plant to tolerate) but cannot say if it is suitable (the correct balance of nutrients are available). For example plants adapted to growing in salt pans etc can tolerate a much higher EC than others.

The reason I have qualified what I have said here is that I don't use EC in growing and I am speaking from theory. Do you have a reference that says that EC can be used the way that you describe?

David

[Phisherman]

So from a given number you are measuring ion concentrations, and that alone doesn't tell you much.

I have a west-coast pad cactus which its mother plant happily lived and flowered on a salty beach of Pales Verdes. It has been living with me for 20 years, grows new pads each year, never flowered. :(

[Alex]

The reason I think using EC as a measure of required nutrient strenght or flushing, is that

1) Short of soil testing, you can use runoff as an indication of what is going on in your soil 2) EC is much more precise a measure than the usual 'use 2 ml per liter' when it comes to nutrient solution 3) EC is very important in hydroponics, so why shouldn't it be in soil or oranic growing media?

It cannot tell you how much of a specific nutrient is available/missing, but it can give you clues about how much to use.

So I just have to wonder - what is the optimal EC for soil of various plants?

I haven't found a lot of literature dealing with this.

Alex

[David Hare-Scott]

No you can use it as an indication of what is running off, that doesn't tell you what is left. Soils have a huge variation in ability to bind ions. I could give you four pots with quite different EC and this would tell you little.

A: high EC due to NaCl = very bad for growing B low EC due to low minerals in all forms = bad for growing C high EC due to runoff of a soluble balanced mix of nutrients = could be good or bad for growing depending on what is left, very wasteful anyway D low-medium EC due to little runoff of soluble ions but adequate bound nutrients = good for growing

I cannot see how this helps, are you talking about measuring fertiliser solutions? Why? If you really want to get accurate measure of solutes then weigh them. I doubt that you need such accuracy.

Because in hydropnics all your nutrients are in solution in real soil they are not, this is key idea which you seem to have missed. Also hydro solutions are less stable than real soil so they need closer monitoring.

Maybe. I doubt it.

I don't see how the concept of a particular EC for a given plant is meaningful much less useful.

That could be because it is not used in that way in practice.

Overall I suspect you are heading a blind alley. I suggest that you learn to build good soil and how to monitor the health of the soil by what it produces which is far simpler in the end. Soil is a very complex medium and we don't yet understand all its working in detail so trying to model the system by measuring just one aspect is pointless in my view.

Once more let me say that I have not gone down this path myself so I am not speaking from experience but I have given reasons why I am doubtful.

David