Kim, mine is an experiment that began last year and not an answer. What I did was amend my soil heavily with peat, wood chip mulch, and garden compost, then added garden sulfur. I'll add more sulfur as needed to counteract the effects of irrigating. Rainfall is neutral but out irrigation water is not. The sulfur is slow acting.

I planted eight blueberries. All but one are southern high bush types. The leaves had good color throughout the summer, not chlorotic, so I think they are reasonably happy. I did lose one but I think it was a water issue not a soil issue. I am interested in seeing what happens this year.

Good point about the water source and sulfur. Out here we can maintain acidity just by mulching with softwood sawdust and leave the peat bogs alone. That way you're just using a lumber yard bi-product (if you can find clean sawdust).

One point I'm repeatedly raising is that the literature is flat-out wrong about how acid a soil has to be to support blueberries. I have seen healthy plants in soils with pH as high as 6.5 where ample organic matter is in the mix and plants are mulched with woodchips. Having said it again, I doubt many who haven't seen it themselves will believe me- how could so many experts be wrong? Because experiments were made in typical agricultural soils I suppose with average OM content.

I agree with HarvestMan. I do have slightly acidic soil here (6.5) last time I tested, yet my blueberries have done fine. (Though I have been known to toss them a little Miracid now and again) That said, I am going to attempt to lower my PH this year using garden sulfur. -Glenn

Hmm, interesting.

Since I'm new to this stuff, could someone give me a quick rundown on effects of different types of wood mulch. E.g. chips vs. sawdust? Softwood vs. other? What about these used christmas trees I have (firs)...could I make use of them?

"Chips" usually means the pieces an inch or more across that are ground up in those grinders the tree-trimmer trucks pull as trailers (or similar larger machines).

"Sawdust" is in two sizes, that from rough-cutting lumber (shreds say 1/4-1/2 inch across) and that from finish cutting (the finer material we typically call "sawdust"). Planing debris (for example from taking a rough-cut 2x4 that is 2x4 inches into the 1 3/4x3 3/4 finished board we usually call a "two by four") can be mixed with either, though more typically the rough-cut sawdust.

"Softwood" typically means conifer (pines, firs, etc.) no matter how hard, and hardwood means from broadleaf trees no matter how soft.

Real simple and easy to follow isn't it?

Ground up fir Christmas trees should be excellent as a mulch. The antiwilt material they spray on it might be some slight problem but sure would not slow me up from using it.

Conifers have less cacium than hardwood(as well as other minerals) and are not going to sweeten the soil. I wouldn't count on sawdust to sour the soil significantly but it should help.

I am currently growing 2 blueberry bushes in soil that is only slightly acidic, about 6.5. They seem to be doing fine, but I am concerned that after a few years of irrigating, the soil will become too neutral for them. Can sulfur be applied to the soil surface (under the mulch) or does it need to be dug in? Will it do any good on the surface? I don't want to disturb the shallow roots.

In mulched soils, surface application should be fine. Acid loving plants only need a fraction of their rootsystem to be in acidic soil- they will get thier iron there.

What about coffee grounds? I've been saving mine to use around acid-loving plants. Please tell me I'm not wasting my time.
Thanks!

My guess is that coffee grinds at best fall in the same category as pine needles- often touted for their acidifying powers but highly exagerated. I wouldn't say you're wasting your time, coffee grounds are probably a useful mulch in any case and blueberries benifit greatly from organic matter. Where I find them growing in nature they are often growing in almost pure loam, particularly when the soil isn't very acid- such as on the hillocks in marshland.

I am planning on planting 4 highbush blueberry bushes in 20 gallon smart pots. I'm going to use regular garden soil and I want to stay organic, since this will be feeding my babies. What should I use to get and keep my soil acidic enough. Thanks for all of the good info so far. I was also thinking about how I would use my the coffee grinds, so now I understand that better.
Rachelle

Dave Wilson has a great section on growing blueberries, and recommends growing them in containers.

Carla in Sac

Here is a link that might be useful: Blueberries on Dave Wilson