my pH is too high

18 years ago

I keep reading that the soil in the northwest is usually acid because of our plentiful rain. However, I just went out and used my pH meter to test my garden soil. I live in Tacoma, and we don't get as much rain here as many other areas nearby. The lowest reading I got was 7.1 and the highest was about 7.5. I did test a few indoor pots and got some really low readings, so I assume my meter is working ok.

I made a list of the plants I have that would like a lower (more acid) pH, but what is the best way to treat them, especially since I should probably try to treat large areas of my garden. I have read that in general, a flower garden should have a pH between 6 and 7. That would mean I should lower the whole garden by about l point except for the lime lovers. Do I really need to do this? And if so, what is the best way?

Daphne

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Comments (2)

reg_pnw7
18 years ago
NO you don't need to lower your pH. Aside from my doubts as to the accuracy of your meter, a pH of 7.5 or less will be fine for anything except the real acid lovers. Your hydrangeas will be pink. Your rhodies and azaleas will be chlorotic and need acid fertilizer. Don't bother with blueberries. Other than that ... I used to garden in extreme alkaline conditions, much higher pH than you're talking about, and the irrigation water was off the scale (over 8.0) with alkalinity. Most plants will still be fine except for the ones mentioned.

Something's making your soil alkaline. Is there a lot of concrete or brick rubble buried in the soil? did it used to be an industrial area? Find out if you're on a soil type that is naturally alkaline, the WSU Co Op Extension people should know, and the Master Gardeners are connected with them so they can find out for you. While you're at it, have them test the pH for you, their tests will be more accurate than a consumer-brand pH meter.

You could just apply gypsum routinely every year, like everyone esle is applying lime routinely every year, but there's no need to obsess over getting the 'perfect' pH. No one has the perfect pH and yet plants manage to grow anyway.

Over time, whatever's been done to the soil in the past to make it alkaline, the rainfall will acidify it. I'd just use an acid fertilizer and not worry beyond that.

I haven't measured the pH in my new garden, haven't seen any reason to worry about it, but my old garden in NW Thurston Co. was a rock solid 6.5 to 6.8 - not terribly acid, nothing like the pHs of 6 and 5 that other people report. Not acid enough to grow blueberries but the rhodies were ok. So not every soil in PNW is acid. But so long as the plants seem healthy there's no real reason to worry about fine points of pH.
gardengal48 (PNW Z8/9)
18 years ago
Gypsum has no effect on soil pH. Amending the soil with acidic soil amendments (cottonseed meal, peat moss) can help but I'd agree that pH is not as critical to plant growth as many believe. Most plants are tolerant to a wide range of pH levels. I'd also agree that home soil test kits often produce less than accurate results and if you apply compost regularly and do not test deeply enough, it can skew the results (finished compost is pretty much neutral in pH). You may want to group the ericaceous plants and other acid-lovers together if you don't wish to go to the effort of amending the entire garden. BTW, I grow blueberries just fine in a pH of 6.5 with an annual topdressing of cottonseed meal.
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my pH is too high

Comments (2)

reg_pnw7

gardengal48 (PNW Z8/9)

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