Thanks for your response. Apparently the soil test labs I mentioned in the original post think the pH needs to be raised. For a pH in the 6.0-6.2 range, the university's soil lab recommended that I add 9-10 lbs. per 100 square feet. And I specifically indicated this was for flower gardens. I have a few sections whose pH is much lower (5.7); 17 lbs. per 100 square feet was recommended.

This was also strange: As stated, lime recommendation for 6.2 was 9-10 lbs. At a pH one tenth of a point higher (6.3), recommendation drops to 0.

What is growing? Hostas, butterfly weed, agastache, blackeyed susans, salvia, Russian sage, several and more Japanese maples, many different cone flower cultivars, lavender, roses, butterfly bush, Joe Pye Weed, etc.

what isnt growing ...

pH is an exponential function ... so it takes A LOT to change it a very small amount .... hence you noted comment ...

as to pine needles ... i like to sum it up this way .. if you put a hundred foot pile there.. for a million years.. you MIGHT change the pH ... im sure thats an exaggeration ... but it sums up my feelings on the effect they might have...

where are you ... there are so few areas where this dramatic of a response is needed ... have you visited a high end nursery.. and asked their opinion as to whether this is common in your area .. or called your local Ag or extension office????

ken

Organic matter, whether pine needles, pine bark, etc. doesn't change the pH to make the soil more acidic. Soil pH is mostly a function of the minerals/inorganic materials in the soil.

I add wood ash which is similar in effect to lime (but in my case free since we have wood stoves) to my veggie garden and occasionally to the lawn, but I don't add anything to the ornamental beds to alter pH. I just plant things that like my pH. There are a few plants that prefer limier/higher pH soil, but there is an incredible range of plants that prefer mildly acidic soil. I have done well even with plants that supposedly like closer to neutral soil such as lilacs and clematis.

Thanks for the responses. Ken: am in zone 7a-6b in the foothills of the Appalachians (Roanoke, VA). And the cooperative extension agent confirmed that I should add the lime to move the pH up to about 6.5. She did recommend, however, that I not till in more than 5 pounds per 100 square feet of lime at a time, waiting about six months between applications. So far, I've only tilled in 5 pounds per 100 square feet. Based on the responses, maybe I should plan on another soil test in early fall.

So, given where I am right now, what would be the ideal (or ideal range) pH for my plants?

Most plants are more than happy within the 5.5 to 7.0 range. Are your plants not doing well? If your plants are happy then the expression "If it ain't broke don't fix it." springs to mind. Here is a link PH

I will also add my 2 cents to the discussion that your pH need no adjusting. The vast majority of plants prefer a soil that is on the acidic side of the scale and yours is just about right where it needs to be!! In addition to most plants preferring an acidic soil, most plants will tolerate quite a wide range of soil pH as well.

Despite what your cooperative extension agent says (and as a professional horticulturist, I question the validity of that advice), raising it a few tenths of a point is not going to make any significant difference in what you can grow or how well it will grow. It is pretty much a waste of time.

FWIW, soils in the PNW tend to have a very similar range of pH as yours and there is seldom ever a need to lime. Maybe the lawn now and again if on the lower range of the listing. In fact, in many cases, folks want to make their soil even more acidic to best accommodate ericaceous plants, like blueberries, heaths and heathers and rhododendrons.

I would also like to reinforce Babs' statement that bark mulches, wood chips or pine straw do not contribute in any significant way to making a soil acidic or an acidic soil more acidic. You would need dumpster loads full to have any kind of measurable effect.

Even though you rcooperative extension agent is supposedly giving you advice for ornamentals, it really is more applicable to lawn and veggies which do prefer soils only slightly to the acid side of neutral. As someone with more than 35 years of growing extensive gardens in my native acid soils, you will be fine with what you have. GG48 is a horticultural pro with at least as much time growing in acid conditions and is giving the same advice and perennial.all is also a pro with much experience; really, you don't need the lime.

Just to add, from my own and my parents' experience over the past 50 years, most everything planted in my garden beds thrives in my southern New England, slightly acidic soil and has done so since they began gardening here when I was age 12. I'm nearly age 70 now and the garden beds have thrived all these years. I edge the beds and move things but don't fertilize. I have 50+ year old established peonies, various ornamental grasses, and established magnolia, a few dozen daylilies, a few dozen established hostas, ephemerals, established perennial phlox...the list goes on. My soil is healthy; I don't use chemicals like Preen or other non-organic fertilizers. I have used organic seaweed extract and organic fish emulsion on occasion. Look around; the planet generally knows what to do and takes care of itself.