Specialty Gardening: Container Soils: Water Movement and Retention II, 1 by tapla

tapla wrote:
I'll try again. ;o)

Melissa - I use either pine or fir bark in all my houseplant soils (no peat at all) so I know that it works well. If you feel the product you have is too small, keep looking for something like in the pic I'll supply at the bottom, or if you have a friend with a chipper, perhaps you could beg him/her to process it to a little finer mesh for you?

I don't often start seeds, but for the few that I do, I use Turface, straight from the bag. Since I always screen my components for bonsai soil, I always have plenty of Turface fines on hand & I cover the seeds with that. It's really hard to beat the jiffy sterile seed starting blends of peat & vermiculite though. They work well, even if they do collapse quickly.

I'll talk a little about EC (electrical conductivity) and TDS (total dissolved solids). They're a measure of what is dissolved in our soil water, so a high level of salt in coir would contribute to elevated levels. I'll explain why this is bad.

Plants take up water best when there are no ions in it - nothing dissolved - no fertilizer - just distilled water. But we cannot do that, or they will starve. We need to add nutrients. There is a fairly narrow band of TDS and EC that is ideal for plants, and it varies by light intensity, temperature, growth rate, and where the plant is in the growth cycle. On the flip side of the coin, if the level of TDS and EC is too high, the plant cannot absorb either water or nutrients, so it could starve or die of thirst in a sea of plenty.

We generally consider the TDS and EC to be an indicator of nutrient levels, but accumulating salts from fertilizers & irrigation water, play an important part, as would latent salts in a coir product (for example). If you want to fertilize at a solution strength of 1,500 ppm, and there is already 700 ppm of accumulated salts in the soil, that means you would only be able to add a solution containing 800 ppm or you would exceed your self-imposed solution strength and possibly create problems in the plants ability to absorb water & nutrients.

I'm not trying to impress you with numbers - pay no attention to them except to help you realize that there is a "ZONE" we hope we can stay in through educated guessing so our plants are at least somewhere between starved & burned up. ;o)

When TDS and EC levels get extremely high, water can be "pulled" from plant cells in exactly the same way that moisture is pulled from ham and bacon. The scientific term for this is plasmolysis, but you and I know it commonly as fertilizer burn.

Ok - now we know there is a zone. We also need to realize that it's important to maintain the right mix of elements and stay within that zone. Why is this important? Well, if you're using the popular 10-52-10 "bloom boosting" blend that's oft touted, you're prolly applying around 30 times more P than the plant can possibly use (in relation to N). You could be fertilizing at the correct zone of TDS & EC, but the extremely high levels of P would automatically guarantee a N deficiency.

I'm going to stop here so you can catch up & absorb this - it's important to understand. I'll leave a pic for Melissa see if there are any questions.

Al

This message was edited Jan 25, 2008 8:58 PM

This message was edited Jan 25, 2008 9:02 PM