Thanks for the info! - This is exactly what I needed to know :-)

Frances

Blueberries are not affected by cedar rusts, so that is not an issue. However, having lots of cedars in Tennessee means you likely have thin limey soils with neutral pH, which are very bad for growing blueberries. I would check the pH before planting. The years of mulch composting may have created a suitable soil, but if not, you may need to acidify the soil.

If you have hard water, that results in lime deposits in your teakettle, it will be necessary to use rainwater on your blueberry shrubs, not tap water. We have hard water, our city wells draw water from the limestone formations that lie below southern Wisconsin. Every August I am out in the yard, running tap water into a bucket, and adding vinegar to lower the pH, before watering the blueberry shrubs.

Wow! I wish I'd found this link last spring! I made the assumption that cedars ACIDIFY the soil simply because they are evergreen and I have one growing happily with a couple of pines out back. I planted a little blueberry bush about 15ft from the other cedar and happily watered all summer with hard water straight from the tap and haven't been able to figure out why it died! Ithought maybe one of my small ones 'helped' and watered it with something noxious. I definately need to study things a little more in-depth even if this bush was an impulse purchase.

The bunnies around my place used to eat blueberry the twigs in the winter. The little buggers also like to hide under my low-growing juniper, beware. I had to resort to putting chicken wire around the blueberrys in the fall to stop the chewing varmints.

How about planting blueberries close to a fir tree, and even using some of the fir tree branches to block the hot summer sun? Can I assume the ground around the fir tree(50+ years old) will be on the acid side...plenty of fir needles there.

I have an aunt that swears that i can mulch my blueberries with cedar bowes. I have never heard of this. I have heard that cedars droppings are toxic to plants. Any advice.

I don't understand how evergreen can acidify soil if they never drop their leaves. Those needles stay on the tree year round so how do they amend soil exactly?

The simple fact is that soil pH is determined primarily by the underlying soil content and secondarily, by rainfall. Plant parts or debris will have no effect. Unless you pile them up by the trailer truck load and even then, the change in pH would be pretty much insignificant.

It is also important to understand what one refers to as "cedars", which is a common name given to a number of trees that have no relationship with a true cedar, Cedrus species. Cedar-apple rust also has no relationship to any true cedar but is related to junipers, some of which are commonly called "red cedar". And cedar-apple rust or any other gymnosporangium fungi only affects the juniper host and members of the Rosaceae family. Blueberries are members of the Ericaceae so immune to these pathogens.

Also, mulching plants with any conifer needles or boughs will not create any "toxic" conditions. At the worst, they may affect the germination of seeds or seeding development but even that is not a given.

And 'evergreens' are only given that descriptor because they hold their leaves or needles through the year. But older needles or leaves will routinely be shed once they no longer fulfill a useful purpose. Just take a look under any evergreen shrub or conifer growing where garden maintenance and clean-up is not high priority and you will see all manner of shed debris. "Never dropping leaves" is a fallacy when it comes to evergreens :-) They shed their foliage just the same as any other plant.....just not all at once.

"I don't understand how evergreen can acidify soil if they never drop their leaves. Those needles stay on the tree year round so how do they amend soil exactly?"

They don't as such (see below, however...), but...trees do remove the resources from the soil around them, so it's not exactly true to say that plants and plant parts don't influence the soil pH or soil resources (same thing, really), around them. Evergreens are famous for drizzling dying needles in piles below them, although it depends on the evergreen (less than one might imagine, I've seen few that didn't, really, that were needle-based). Yes, we can argue for days about "needles" and the definition thereof, but they do age and are replaced.

The full explanation follows.

As they compost in place, they rot and generally get pretty close to neutral pH (most sources say 6-8. That seems about right from casual measurement).

That compost has a lot of free binding points for resources (you can look into CEC--cation exchange capacity--if you want). Those can't just stay empty, it's a matter of energy potential. So they'll grab onto a hydrogen ion from water, letting the oxygen go back into the air. Hydrogen ions are weak acids.

The overall result is a weakly acid pile once all is said and done and it's gone from compost to indistinguishable from dirt. How acid depends on the CEC, which depends on the initial composition and the admix into soils. This is not simple. But if you isolated it back out and measured it, let's just estimate it at pH 5.5-6, but a volume low enough that it's not having too terribly much impact on the soil overall.

That's easy to fix with a little calcium, or whatever a soil test recommends. The hydrogen only weakly bonds. The calcium has a dual, and much stronger, bond.

Any plant pulls calcium (in larger amounts), magnesium (smaller), and potassium (in the middle) from the soil, reducing pH. A soil test would be required to tell you how much, but it does tend to drift faster within a tree's root system than otherwise.

Succession comes into play with other plants like dandelions, which don't mind absolutely awful soils. So the situation isn't simple here, as those will throw deep tap roots and mine resources from deeper in the soil, bring them up, and overall richen the topsoil beyond what it had previously. Deeper tree roots can do exactly the same thing.

But those resources end up bound into the tree's wood, leaves (needles, in this case), and roots.

Tapped from the soil, however, leaves space only for hydrogen again, as described above, or for something else entering soil solution from the solids (aluminum, a strong acid and also toxic, is another possibility, but you could get calcium if you have undissolved calcium carbonate in the soil too).

As it relates to blueberries and cedar trees, the rough answer is, "probably not." Cedars like a 5.5 to 7.2 pH (depending on the species, I didn't track back that far as the sub-question didn't really apply). Mine do very well at 6.2, Thuja standishii x plicata. Blueberries would prefer 4.5 to 5.5, so there isn't much overlap there. Trying to grow them too closely together is not going to end well, creates a gradient in the soil that's awfully sharp, and one would be playing games with sulfates and calcium that I really don't want to think about. And, as always, mind the sulfur at the surface; it tends to turn to sulfur dioxide and nobody needs the atmospheric smog and greenhouse gasses. Dig it in, but mind the root systems and patches of extremely low pH.