Hi Krista:

This question has been asked before, so I'm going to give you a direct quote from our Extension Agent:

MYTH: Ponderosa pine needles make the soil more acidic (low pH).

REALITY: The notion that pine needles change the soil pH so that nothing will grow or that it will damage plants has been out there for years. The truth is pine needles do not make the soil more acidic. It is true that pine needles have a pH of 3.2 to 3.8 (neutral is 7.0) when they drop from a tree. If you were to take the freshly fallen needles (before the needles decompose) and turn them into the soil right away, you may see a slight drop in the soil pH, but the change would not be damaging to the plants.

If you run pine needles through a shredder they will break down faster.

For those of you that leave the needles there on the ground, they will begin to break down naturally and the microbes (decomposers) in the soil will neutralize them. So, you can leave them there (if you’re not in a wildfire prone area). They are a good mulching material that will keep the moisture in, suppress weeds and eventually add nutrients back to the soil. You can also add them to a compost pile; they will slowly break down over time. If you run them through a shredder they will break down faster. A general rule of thumb is not to add more than 10 percent of pine needles to your compost pile.

If you are having difficulty growing other plants under your pine trees it is likely due to the fact that evergreen roots are numerous and shallow and compete for water and nutrients. The shady conditions under a tree can also make growing other plants a challenge. 

Amy Jo Detweiler, OSU Extension horticulturist

There may be other things impacting your garden yield.  It's true that our native soil has very little nutrient value.  Adding compost or aged manure can help remedy this.  It could also be the location of the beds.  Are they getting enough sun?  Are they protected from frost pockets?  What are your watering practices? Are you waiting for the soil temperature to rise to at least 55 degrees before planting?  Are you planting varieties that will mature within 65-75 days?  Our cool nights generally require you add 14 days to the date on the seed packet.  I'm attaching a bulletin that addresses these issues in more detail and may help you succeed in our challenging environment.
Growing Vegetables in Central Oregon

Wishing you much success,