Droid, where'd the pH number come from? It seems to be quite high for tap water. A pH of 7.0 is 'neutral'.

Generally, tap water is less acidic than rainwater, distilled, and RO water and the MSU formulation accomodates that.

Most orchids prefer slight acidity - pH of 6.7 +/- 0.2.

I didn't answer your question!

The 'Well Water' formulation is meant for tap water, and the 'Pure Water' formulation is for rain water, etc.

However, if your pH range is accurate (9+), you've other problems to solve first.

The data comes from the MWRA monthly water quality report, this is an extremely large water distribution system for a large portion of eastern MA. The link to the report is given below, the data quotes is from that last page, the relevant data is in the column labeled 'Carroll Water TP Fin. Water Tap (Treated)'.

Our water is soft, and has very low alkalinity, so the buffering capacity is also quite low. The PH is therefore set quite high so that during transport through the water system the PH will never drop low enough that lead and copper will leach from old pipes (an important consideration in an old city where some WATER MAINS are still made from lead). If you look at the data in the table, the pre-treated water is at a PH of 7.3, and the treated water is at ~9.5.

I might have to get both formulations and do some testing to see how far the two formulations change the PH. My primary concern is the lack of Mg and Ca in our water, so I think I will need to supplement that is one way or another.

I also found this post http://forums2.gardenweb.com/forums/load/orchids/msg0210534117581.html where tee530 designed a custom 'MSU' fert for WRMA tap water, I might have to track them down and see if they is willing to sell some of this to me :-)

Thanks,
~Droid

Here is a link that might be useful: MWRA April 2007 Water Quality Report

nice to see that some people read the old posts... :-)

Droid, IMO, you are on target. A pH of 9.3 looks high, but with the low alkalinity, it should pose no problems. (Consider the analogous relationship between temperature and heat capacity: a sheet of paper has low heat capacity, so even heated to 451F it isn't a danger to pick up; cast iron, however, is a different matter...)

I find our metro water fine for orchids. I would use the MSU RO water formulation to get the Ca and Mg up into ideal ranges. There was nothing special about the fertilizer formuation I posted a while ago, it is nearly identical to the MSU RO formulation except that I adjusted the pH of the stock to give me a final pH of 6.5 with MWRA water. You can do the same to commerical MSU formulations with nitric acid, phosphoric acid, or even vinegar, if you choose.

Before I brewed my own fert, I alternated calcium nitrate and magnesium sulfate (epsom salts, near the band-aids in the supermarket) to the watering once a month.

Happy growing! In our climate, it ain't the water and fertilizer that's going to limit your results....

I find that Dyna-Grow Protekt also changes the ph.

Tee,

Thank you for the response. One more question questions: Have you measured the PH of MWRA + MSU RO in a typical fertilizer concentration? I have some fertilizer acidifers that I use with some of my acid loving Bonsai, so I am sure I can find a proportion that works for Orchids as well.

Oh, while I have a local here... Any recommendations for a good place to look for orchids and supplies in the area?

Thanks again,
~Droid

Since the calcium and magnesium content are so very low, definitely go with the RO water formulation and adjust pH if necessary. And it may not be. With so low alkalinity (buffering capability), the pH will swing wildly either way with slight changes in dissolved solids, And worrying about the pH of the fert solution is really, truly the last thing on earth to worry about unless you live in an area - like Florida or the Southwest - where the alkalinity (calcium carbonate content) is consistently very high.

Here in NYC the water is similar, except the dissolved solids are even lower (60ppm - ish) and the MSU RO version has been working very nicely for me for a couple of years now.

One thing: you note that the dissolved solids are "mostly" some stuff including sodium. Depending on how much sodium there is exactly, it could be a problem for sensitive plants like some paphs, phrags, and many of the pleurothallids. If the sodium is too high for what you want to grow,

Droid -

Nope, never checked the pH of the commercial MSU RO with local water, but I'm with NYC on this one: likely not a problem.

As for orchids/supplies in eastern MA, Mahoney's Garden Centers occasionally have interesting plants (I picked up a Paph delenatii in bloom this spring for $20) but poor selection of supplies. Conversely, I've found Russell's to have poor orchid selection, but better in choices of bark/perlite/sphag, etc.

Neither of these places is an orchid specialist, of course. If you haven't been, it's worth it to visit the Lyman Estate greenhouses in Waltham. Not the biggest or showiest place, but parts of the greenhouse complex are well over 100 years old, and when the citrus section is in bloom, it's heavenly. Orchid section is crowded, poorly organized, and simply a delight to nose through. There is a for-sale section too, prices a bit on the high side, IMO, but some neat species that you won't see at Home Depot.

If you want to see and buy the terrestrials (and who doesn't?) get yourself out to Garden in the Woods in Framingham. Cypripedium parviflorum and pubescens are blooming now, C. kentuckiense in a week or two, and C. reginae later in June/early July. Grow these well in your backyard, and you can thumb your nose at our Floridian forum members who kick our butts on just about every other genus... :-)

"If the sodium is too high for what you want to grow, "

didn't finish that sentence. If it's too high, the only real answer is reverse osmosis, or using rainwater or another source of low-sodium content water either to dilute the tapwater or to use by itself.