Feed directly, or pre-water first?

[Ray]

I know this has been discussed, and I stand by my recommendation to NOT pre-water, but I was challenged on that by someone who had “275+ppm” mineral-laden tap water, so I thought I’d share my logic:

When using non-purified water supplies, I think the concept still applies - maybe even more so. In my mind, there are two processes to deal with: saturation and ion capture, and both have limits.

Scenario 1 - one watering with pure water and fertilizer: the roots become saturated with the solution and as many nutrient ions as possible are captured by the available sites.

Scenario 2 - initial, plain, pure water irrigation, followed up with fertilizer solution: the roots become saturated, reducing the absorption of the fertilizer solution, so fewer ions are captured.

Scenario 3 - one watering with “275+ ppm” water and fertilizer: the roots become saturated with the solution and as many dissolved mineral- and nutrient ions as possible are captured. Yes, it will be less nutrition, as the dissolved mineral in the water will occupy some of the “capture sites”.

Scenario 4 - initial, “275+ ppm” water irrigation, followed up with fertilizer solution made with the same water: the roots become saturated and capture as many of the dissolved mineral ions as possible with the first watering, reducing both the absorption of the fertilizer solution at the second, which already allows fewer ions to be captured, but the sites available to capture more are already occupied, so even fewer nutrient ions can be captured.

[WaterWitchin]

Makes perfectly good sense to me, Bill. I'm not of the pre-watering crowd regardless of whether using pure water or tap water.

[tmoney]

Originally Posted by WaterWitchin

Makes perfectly good sense to me, Bill. I'm not of the pre-watering crowd regardless of whether using pure water or tap water.

all that does make sense, except for where you called him bill. not to change the subject, but what am i missing? i thought your name was ray??

[WaterWitchin]

You're just a newer member... it's my nickname for Ray. Bill Nye, Science Guy...

[Shadeflower]

I'm with you Ray, orchids absorb all they can as fast as possible and become saturated.

We know how little fertilizer orchids need because we do not pre-soak our roots so nothig gets wasted.

I always wonder, honestly, how people get away with fertilizing theirs much stronger but if they load their roots with plain water first and then top it off with really heavily fertilized water then all that fertilizer will just run off into the drain and thus not burn any roots!

So if it prevents these growers burning their roots then by all means let them soak the roots with plain water first so the orchids can only absorb tiny amounts of fertilizer afterwards

[SADE2020]

Beside the saturation and absorption, I have to disagree in maybe another scenario:

If the roots are completely dry and are in the sun or with a lot of heat (vandas, catts, some dend) the tender tips of the new roots can burn when the fertilizer is applied without first moistening the plant.

[Ray]

Originally Posted by SADE2020

Beside the saturation and absorption, I have to disagree in maybe another scenario:

If the roots are completely dry and are in the sun or with a lot of heat (vandas, catts, some dend) the tender tips of the new roots can burn when the fertilizer is applied without first moistening the plant.

Not if it's a dilute solution (which is also my preference).

[Roberta]

Originally Posted by SADE2020

Beside the saturation and absorption, I have to disagree in maybe another scenario:

If the roots are completely dry and are in the sun or with a lot of heat (vandas, catts, some dend) the tender tips of the new roots can burn when the fertilizer is applied without first moistening the plant.

I'm thinking that if root burn is an issue, the fertilizer is too strong. In nature, the first little bit of rain washes the "stuff" down from the canopy, so that is the best time for the orchid to grab it - most efficient when it's dry to start with. But that does seem to relate most to epiphytic plants growing bare-root (mounted or in trees). For a plant sitting in a pot, there is more time for it to absorb fertilizer, since it doesn't wash away quickly as it does for a mostly-bare-root plant.

Another instance where, I think, advice needs to seen in context.

[estación seca]

The people who have written above understand this, but for people learning about fertilizer: Watering every time with a relatively dilute fertilizer solution instead of plain water makes a lot of sense.