I was told the same thing just recently as what Dave says about the mulch. I've been considering blueberries, but our soil is so close to neutral that I didn't know if I wanted to put the work into adjustment or outright replacement of the soil. What is your average soil pH, Brandon?

Coffee grounds aren't that acidic. Not when you are talking about most plants and the fact that they prefer slightly acidic conditions. I say that with confidence because I have measured the pH of several batches and different brands (Folgers, Maxwell house, Starbucks). Due to all the hype out there I expected the pH to be 5.5 or lower. Not so. Never below 6. Generally, 6 to 7 isn't considered acidic in the gardening world even though it is technically acidic because so many plants prefer the 6's as ideal. When you say acidic loving plants, you are usually talking about plants that prefer below 6 (like your blueberries). I just thought I would share that. Oh, and worms don't like acidic foods as much as those closer to neutral but they thrive in coffee grounds. That's just further evidence without even taking measurements. Why did I just share that info? Because if you use coffee grounds to lower pH in soil that has lower pH than the grounds, I would think you will raise the pH, even if only temporarily. I don't know this for sure from experience, but it might be something to look into.

Contrary to popular opinion Pine Needles and Oak leave added to soil will not change that soils pH to a more acidic one. Research done by Abigail Maynhard, pHD in soil science at the New Haven Agricultural Research Station in New Haven, Connecticut showed that adding large volumes of Oak leaves or pine needles did not significantly change the pH of the soil in those test plots. After years of adding compost and shredded leaf mulch, mostly Oak leaves to my soil that tested at 5.7 pH in the 1970's now tests at 7.2 pH without adding any lime.

The best way to acidify soil I have found was with elemental sulfur. In the soil, not in the compost. If you have a high pH, pine needles or oak leaves may lower it (just like any other organic material would) but they will not make it acidic.

tj

It's been my experience that many gardeners tend to over think the soil pH thing. It is always good to know what the base pH is but in most gardens it will vary somewhat depending on location. And obviously, if your soil is skewed dramatically one way or the other, you may need to make adjustments. But otherwise, attempting to achieve a precise pH is going to lead to a lot of frustration.

Most plants have a range of soil pH they will tolerate, if not thrive in. And that range tends to be pretty wide, considering the pH scale is logarithmic with a tenfold change from one pH level to the next. As noted above, the vast majority of plants will grow happily in slightly acidic to nearly neutral soils, broadly defined as 6.0 to 7.0. If your soils test in this range, attempting to alter the pH is generally unnecessary.

Many resources will state that blueberries and other acid lovers or members of the Ericaceae need to have soils that test out at around 5.5. Some will even state that blueberries will not do well in soils with pH above 6.0. This is by no means absolute - it is perfectly possible to successfully grow blueberries, rhododendrons and azaleas, heaths and heathers, etc. at much less acidic levels - those in the 6.0-6.5 range.

Here in the PNW native soils tend to be slightly to moderately acidic - it is very unusual to find soils that test much below 6.0. Yet many species of acid loving plants are native to this area and all manner of acid lovers - rhodies and azaleas, heaths and heathers, many conifers and broadleaved evergreen shrubs grow happily here with minimum attention to pH and nutrient availability. And we also have some of the largest commercial growing operations in the country for blueberries and cranberries.

So what this boils down to is it is not a requirement to have soils with a pH of 5.5 or lower to be able to grow these plants and grow them well. If your soil tests as slightly to moderately acidic, these plants should do just fine. While it may be considered heresay on this forum, this is a case where incorporating peat into the planting hole is well-advised and recommended by the largest producer of blueberry plants in the country, Fall Creek Nursery in Oregon. Not only will it provide for good blueberry planting conditions for virtually any soils but it will help to retain soil moisture which is essential for these plants. Fertilizing occasionally with a product formulated for acid lovers can help to maintain correct levels - most of these contain acidifiers and also provide most of the trace elements that are less available in less than ideally acidic soil. Or mulch with cottonseed hulls or topdress with cottonseed meal or peat and then mulch with bark or pine straw. An occasional application of elemental sulfur can help as well but don't overdo as sulfur can cause damage to plants if applied heavily or frequently.

Even when folks use acidic materials to make compost, it is my understanding that it comes out between 6.0 and 6.5 pH.

The Cornell Composting site may have info in that area.