How locally can pH be altered?

Saint Louis, MO(Zone 6a)

I've never seen anything about this in discussions of methods to raise and lower soil pH and so on.
Yet it must be an issue for just about any home gardener who isn't dealing with a single crop in a large space.

Maybe everyone else just knows, but if so, please enlighten me!

Here's an example:

I've inherited a perennial bed that has azaleas mixed in with other plants that like a fairly akaline soil.
The azaleas are clearly in need of a more acidified soil.

One day I may disentangle all these plants with contrary needs.
But for now, what I wonder is:

if I amend the soil to, say, the drip line of the azaleas,

how much am I going to affect the pH in the soil *beyond* the drip line (and how far beyond).

Everything that discusses altering pH (whether up or down) always seems to discuss it as if the plant you're doing the amending for was the only one in its own little universe, or surrounded solely by its own kind.
But life in the garden just isn't like that...
any insights much appreciated!

Stanford, CA(Zone 9b)

I treat my hydrangeas so the soil is quite acid. I like them blue so I treat them and it doesn't seem to bother the plants ariound them. I actually have neutral to acid soil everywhere. I have to treat my acid lovers like citrus, azaleas,etc. several times a year to keep the acid up. When you're talking about acid soil - Azaleas only need a slightly acid soil - so if your soil treatment affects the surrounding area and you're only treating to the dripline it shouldn't be a problem. The other possibility is to underplant them with a more acid loving ground cover, Ajuga works very well here. Creeping mint is another favorite of mine. It's not invasive and looks like moss. Then you don't have to be so careful. If you already have alkaline soil, it's going to be really hard to make it too acid. Just be sure to treat with a good azalea food that has trace nutrients along with whatever else you're doing.

What alkaline loving plants are we talking about anyway?

Waxhaw (Charlotte), NC(Zone 7b)

You can change pH on a per-bush basis. that is perfectly fine.

Saint Louis, MO(Zone 6a)

doss and kdj,

thank you for the replies.
doss, I wasn't thinking so much about this one particular spot (I described that one - which does exist - just as an example to make the question clear). It has just struck me as an interesting aspect of soil amendment (about how soil responds to amendments really), and it's always seemed surprising that it doesn't get discussed even in otherwise quite comprehensive discussions of how we may impact the soil (for better and worse) by the things we do (and don't do!).

kdj, you're saying that steps taken to acidify will remain very localized then? That's how I've gone about it, more or less by default, the few times I have really tried to affect pH, and it has seemed to work. I just wonder how that works, chemically speaking, since so many things will leach through soils and spread and so on. I suppose it may be mainly a matter of not overdosing for the area you're trying to acidify. And perhaps it's just as simple as that, and *that's* why nobody discusses it?!

Stanford, CA(Zone 9b)


I actually never thought about whether or not it would work either. It's good to puzzle over. I've come up with some ideas. One clue is that I can grow almost anything just at the dripline of my English Walnut tree. Anything closer than that has to be something that grows under English Walnuts which are pretty toxic.

I use acid fertilizer and regular fertilizer right next to each other. There is no question that I carry them around at the same time and treat each plant with what it needs. I feed plants at different times too. Bulbs early, Camellias just after bloom, lots of other things once a month with liquid fertilizer once a month. Twice I just can't manage. Even Bearded Iris rebloomers get food about a month after each bloom until fall.

I just make sure that I don't put high nitrogen fertilizer near blooming plants like Iris or vines or roses. That's the one thing that's a no-no if you want good bloom. You'll have lots of green growth though. :-) I think that I give a wider berth to them. On the other hand, the Iris in the photo is only a foot from the lawn which gets a really high nitrogen food. And it never stops blooming. It's blooming now.

It's a perfect example of what you're talking about.

I feed the Japanese maples special food to keep them from getting root-rot and hydrangea food plus "blue" adjustment for the hydrangeas. And the clematis get a timed release food as do the Dahlias. They need a lot. Then there's citrus........You should see my cupboard. Some people might think that I'm crazy but my garden sure looks great in the summer time. Can't wait to see that new Hydrangea on my fence. It should be here any day now. And I love the idea of Hydrangea trees. Never heard of it. I think that I've lost my train of chemical thought.

I don't feed overenthusiastic plants like the Morning Glorys. Why get myself into even more trouble? (LOL)

You got more than you paid for. Hope that it's not too overwhelming. But you see I do believe in local plantfood like you do and now I know why. It's funny how we just "do" things without thinking. Thanks.

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Saint Louis, MO(Zone 6a)

hello doss,

thanks for all that "food for thought"! I suppose you're exactly right and thinking about it as a form of fertilizing is the right model. It has just seemed curious to me that a garden could, in effect, be a honeycomb of ultra-micro pH zones that don't "leak" into one another. But if we think about fertilizing, it immediately becomes clear that fertilizing one half of my field will not do the job for the other half...

another spectacular photo from your spectacular gardens. What is the multi-stem maple in the background? And the green-so-green succulent looking plant in the foreground? (it looks almost like a big aloe by its form, but I think I can see that the surface texture is quite different).

Stanford, CA(Zone 9b)

I wish I knew what it was. I should ask at our Japanese Maple specialist. It has fabulous red seed pods. Here's a close up of it a month ago. It's a very hardy cultivar - full sun and wind don't bother it. The tree is about 20 years old. It's the first one to leaf out in the spring.

The bright green thing is a "foxtail fern". I only know it by that name. It grows anywhere. Shade, sun, you name it. And it it's a bright spot where ever it's planted. I'll look for a closer photo of the fern.

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Stanford, CA(Zone 9b)

I thought that you might want a photo of the whole tree. My hands shake so I really need to use a tripod and I didn't here. That'll teach me.

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Stanford, CA(Zone 9b)

That's hysterical. It's a photo of an Hydrangea in February. Here's the fern - which I believe is a misnomer.

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Stanford, CA(Zone 9b)

Here's the tree at the end of February.

As far as Ph. I've heard that changing the foliar ph can get rid of powdery mildew. Ever hear of it?

Thumbnail by doss
Saint Louis, MO(Zone 6a)


I just thought you were showing me a "puppy" shot of your tree, till I noticed the leaves! Nice hydrangea though. What kind is it?

foxtail fern - PlantFiles to the rescue once again (what an amazing resource being built collectively): Foxtail Fern 'Meyersii' (Asparagus densiflorus)
It's lovely.

As is the maple, whatever it may be. Do you ever put your photos into PlantFiles? That one with the seed pods would be a nice addition if/when you identify the cultivar. I really appreciate photos that show various details of the plant, plus ones like your last shot here, that show the whole. So often a catalog will only show a plant in its most spectacular phase, or show only its bloom, etc., when what you really want to know is how it's going to look the rest of the year. PlantFiles is so good for that (among other virtues).

altering foliar pH to deal with powdery mildew? I haven't heard of that, but want to! Powdery mildew does seem to thrive here. Altering pH down I'm guessing? A foliar iron sprays for example?

Stanford, CA(Zone 9b)

I can't find the website of the people who told me about the ph adjustment and they didn't send me a bill with the products I bought there.

But you might laugh. I found a site that said when you feed Clematis you should feed 50 square feet around them. At least!

Duh! I just called another website and they said that you use a product called Ph-up. And you get the diluted water to 8 or 9 and put it on your plants. Evidently mildew can't live in that much Ph. There's a measuring device that measures the ph of the water.

I asked him about fertilizing by plant and he said it's the only way to do it.

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