Flushing with each watering - is monthly flush needed?

[JeffreyR]

As Ray currently suggests, I am filling the pot with 25ppm fertilizer with each watering and allowing it to flush out of the 2 low drain holes.

I see messages suggesting that a monthly flush with pure water (no fertilizer) is needed. But I don't believe that I've seen that on Ray's how-to.

Is the monthly flush recommended in all cases? Or just for those who don't fertilize / flush with every watering?

Thanks again

[Orchid Whisperer]

The answer that is probably the safest, general answer is "yes". Do a monthly flushing.

This is especially true if you use tap water with significant total dissolved solids. If your tap water is 100 ppm (+ or - 50 ppm), you can probably do a monthly flush and that should be good. This assumes your plants live indoors and are not receiving direct rainfall. Your water utility can provide information on tap water TDS, and may even have that information on their website.

If you have water higher in TDS than the above range, I would flush more often, with higher quality water (rain, distilled, de-ionized, reverse osmosis) if possible.

I greatly reduce the amount of flushing that I do by growing outdoors in warm months, and watering with captured rain water when growing indoors in cold months. I also greatly reduce fertilizer in winter.

[JeffreyR]

Thanks.

The water authority tells me that my hardness (not quite the same as TDS, but close enough?) is usually in the range of 85-120 ppm, with some seasonal fluctuations.

I also run the water through 2 filters... activated carbon/filter down to 20 microns, followed by a finer carbon/lead-out filter that removes lead and filters down to 0.5 micron. Our water is pretty good, so this is mainly for taste. I'm assuming (hoping) that this does not affect TDS in either direction?

With that 85-120 hardness in mind, I'll continue to water/flush with the filtered water and fertilizer at 25 ppm N, and do a monthly flush with distilled or RO water.

Sound right?

[Ray]

Water with 25 ppm N is mighty close to plain water, so a monthly flush with plain water isn't necessary. It certainly can't hurt anything.

Hardness is NOT the same as TDS, but may be close. Hardness, usually expressed as ppm (mg/L) CaCO3, is the calcium-, magnesium-, and iron carbonate content, but there can be other ions in solution to add to that.

You are correct that your filtration is doing nothing to reduce that.

At its highest, your water quality is close to the upper end of the levels most professional nurserymen prefer. It's not "fatal" to use it, but if you have a ready source of RO water, your plant would do better if you use that routinely.

[claypot]

I fertilize every watering and never flush. With +/- 700 plants that has worked fine for me, but bear in mind that orchids are very weak feeders so "weakly weekly" is my motto.

[JeffreyR]

Sorry for the change, but I've got an update on the water here. "The guy" from the water authority called and let me know the real deal, rather than what is posted on a many-years-old map. The map assumes that they are running their wells as well as surface water. For the past few years, they've only used the wells in emergencies when demand is incredibly high.

The hardness of my water is in the range of 70-80 ppm, not 85-120. And the TDS, which I did not have before, is around 150.

Does this lowered hardness and possibly increased TDS change anything re recommendations?

Thanks for your patience.

[Orchid Whisperer]

The 150 ppm TDS is probably ok for many orchids. The 70-80 ppm hardness indicates moderate hardness, also Ok (you probably will have adequate calcium and magnesium, which many orchids need, and won't need to supplement).

If the utility is not getting water from wells, they are getting it from the river. Unlikely that river water intakes are right at Philadelphia, probably upstream where the bad TDS components (like sodium) are most likely low. IMO, I think your water supply is fine, but I would still flush monthly.

[JeffreyR]

I'm in Montgomery county, where our water is considerably cleaner than in the city of Philadelphia. It is surface water, as you suggested.

Thanks for the guidance.

[richardb]

I really wonder why people get so worried about such things as TDS. I have grown successfully since the 1980's and never bothered. When I was in Colombia looking around the natural habitats I never saw the Almighty measuring TDS of precipitation and juices running down rain forest trees before letting it rain. But what a stunning display everywhere. Orchids are plants. They take what they want and ignore what they don't want - be sensible just don't offer them anything toxic. Enjoy your plants and don't over complicate things. Keep it simple because that is what orchids like best.

[Roberta]

Well, if the TDS is in the 600-900 ppm range as it is in some localities near me, it can be a problem. But I don't think that's an issue for the OP.