conifer needles for amending garden soil?

I posted this earlier to the tree & shrub forum, but no replies yet. Maybe here someone can help me.
I have a privacy hedge of 9 Skyrocket Arborvitaes that I planted about 6 years ago. They are growing great, but I just noticed that the interiors are filled with brown needles. Yesterday I went through and cleaned them out- I got 3 big trash bags full! No insects or disease- I think I just planted them too close, and this year with our water restrictions they were not watered enough. I poked holes in the soil and gave them a good soaking and hosing down. My question is this--can I use the bags of needles to amend my garden soil? I grow a lot of veggies, herbs & flowers, and am always looking for good additions. It seems that they would be good to add bulk and drainage to my many raised beds. Any advice is welcomed.

if not for amending, then at least for mulch,but seeing as they come from an evergreen, i might would just reserve them for acid loving plants such as tomatoes, blueberries and hydrangeas

Thanks, jmc- I will use them-- I don't throw anything away unless it is diseased or has insect problems- these nedles are really clean!

I doubt several bags of acidic mulch would impact your soil pH significantly. In addition, isn't the soil pH in your area alkaline? That's what I am seeing on soil maps. If so, add lots of acidic mulch.

I am not really concerned about changing the ph- my veggies seem to do very well, so I will add the needles to "fluff" up the soil and help water distribution.

If the needles are dead they are no longer acidic. Even if used green they won't shift soil pH is used as mulch. If used as an amendment, it takes many years of heavy incorporation to shift the soil pH by anything significant.

I'd say you have a good use for "waste" material.

I have never heard of or considered Tomato Plants acid loving, if they were they wouldn't grow here. Blueberries require acidic soil. The color of the blooms will change on hydrangeas depending on the on the soil PH but they will grow in either.

Nicole's explanation is on target. Green needles are acidic and brown are not. Either way, they won't shift pH. As for tomatoes, they prefer acidic soil. Whereas 7 is neutral, they prefer below that and down to 6. That's not to say they don't tolerate a wide variety of conditions.

I just meant that there are some plants that won't grow in anything but Acidic conditions, tomatoes aren't one of them.

Really, I wasn't asking because I am concerned about the ph--I only wanted to know if they would be beneficial as a soil additive or detrimental-- thank you all for the input. I plan to mix them in when my plants are removed and let the soil "digest" them over the winter. (not literally- I know they will be slow to break down)

nicole, so if it is true that the brown needles would not provide any acid, then what about the theory that adding pine needle mulch will make soil more acid? The pine needles are dead when used as mulch- just asking out of curiosity- as I said, I am not concerned with the ph.

It's not a theory, it's a myth, and one often repeated. I suspect that the "common knowledge" that pine trees & needles make soil more acidic is based on the fact that conifers, Vaccinium spp., Rhododendrun spp., and other acidic loving species thrive in acidic soils. Plus maybe a little laziness: it's going to take more than a little pine straw on top to make alkaline soil acidic enough to grow healthy blueberries.

pH of green pine needles is about 3.6
pH of brown pine needles is about 6.0
pH of composted pine needles is about 6.5
For comparison, pH of non-polluted rainwater is 5.0-5.5

When pine needles are used as mulch, organisms break down the acidic chemicals in the organic matter. In controlled tests, any rise in acidity was insignificant and short lived: under 3 weeks.

However, in long term studies of pine needles used as a sole, heavily incorporated soil amendment, the pH does slightly shift. But this takes 10-20 years. Shorter term studies (see quote below) say no. I don't know if the mechanism is known, but it may have something to do with the lower oxygen conditions below the soil surface and the kinds of microorganisms doing the decomposition when you get down several inches below the surface.

http://www.ars.usda.gov/research/publications/publications.htm?SEQ_NO_115=223401
"Experiments were conducted in which loblolly pine straw with or without nitrogen fertilizer (field)... affected topsoil acidity in comparison to an unmulched control during 12 mo. In both experiments, the mulches were mixed into the topsoil to accelerate rotting. Pine straw did not increase topsoil acidity in the field experiment, while nitrogen fertilizer increased acidity... We concluded that there was little potential for pine straw mulch to acidify soils when a typical rate of pine straw (17 tons/acre) was applied."

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Additional reading:
http://ucanr.org/sites/UrbanHort/files/80212.pdf (page 2)
The 2007 paper from mulch guru Dr. Linda Chalker-Scott's is not available online, I don't think.

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On the flip side, in a study in Poland they planted both conifers and broadleaf trees on acidic soil in what was formerly a Scots Pine forest. After 30 years, the conifers didn't change the soil acidity either way (as expected), but the broadlead tree leaf litter DID make the soil more alkaline!

WOW! That's a lot of knowledge- thanks a lot-

Wow, that's a lot of pine straw mulch! Great info