Ask Mr. Smarty Plants

First, we need to establish some plant identities. We found several websites referring to a salvia as Texas Hummingbird Sage, or Texas Sage or Hummingbird Sage; for instance, this one from Fine Gardening, this one from Seeds of Change or from Dave's Garden,  all of which refer to the plant as Salvia coccinea, which we find in our Native Plant Database as Salvia coccinea (Scarlet sage). There is also a plant in our database referred to as Salvia spathacea (Hummingbird sage). According to this USDA Plant Profile Map, Salvia spathacea is endemic to California; i.e., growing nowhere else in North America. When we check the Plant Profile Map on Salvia coccinea, we find that, while it does grow in a few places in Georgia, it is not reported as growing in Jones County, in Central Georgia.

We are going to put all this confusion down to creative trade names, and say that the best chance for a salvia growing in Georgia being the one you have purchased as Salvia coccinea (Scarlet sage). In this research, we found no indication of a conifer being poisonous to any sage, so let's look a little further.

Growing Conditions for Salvia spathacea (Hummingbird sage):

"Growing Conditions

Light Requirement: Part Shade
Soil Moisture: Moist
Soil Description: Various mesic to slightly moist soils.
Conditions Comments: This perennial is easy to grow and deer proof."

Growing Conditions for Salvia coccinea (Scarlet sage):

"Growing Conditions

Water Use: Medium
Light Requirement: Sun , Part Shade , Shade
Soil Moisture: Dry , Moist
Soil Description: Caliche type, Sandy, Sandy Loam, Medium Loam, Clay Loam, Clay
Conditions Comments: Scarlet sage reseeds easily and will grow in the shade. It has pungent foliage that makes it fairly deer resistant. Periodically trim and deadhead to keep it bushy."

From that, it does not seem that simply shade from a conifer or any other tree would have caused either salvia to die. We do know that the fallen plant material from conifers tends to be acidic, thus influencing the soil beneath them to be more acidic.

Frankly, we can't verify that conifers kill salvias. Heavy shade from a nearby large conifer, the acidity of fallen needles from a conifer or just competition between the salvia and the conifer roots could all affect the outcome. Mr. Common Sense says if you have had this problem in your garden, don't plant salvias under conifers.