Where I live there is so little sun at the dark of the year that I can't even keep a pot of chives green on a warm window sill, let alone grow any herbs outdoors. Even the Siberian buckwort has given up for the year and its berries turned to mush. The ground has been frozen for weeks and it will be frozen for another two months yet, though there isn't any snow.
You might think an herbalist has nothing to do but read dusty herbal tomes at this time of year. And some of that definitely does happen, but there is still one plant that gives its medicine in this season. And it is one you are likely to bring indoors one way or another. You might as well make some immune-boosting tea while you're at it
That is, of course, pine needles.
However, with pine and other conifers a warning has to be put out right up front. Not every Yule tree is a pine and there are conifers related to pines that are toxic, even lethally poisonous.
Yew, a wonderfully magical but deadly tree, is the primary danger for humans. Consumption of the needles or berries, even in small amounts, can kill. Yew is often used as a decorative hedge and could be confused with spruce or fir.
When I was a child, I often ate the new growth of fir needles while walking in the woods. We called them "friends" as a slurring of "fir ends." And they were piquant but generally tasty as well as high in vitamin C. Fortunately, we didn't have many yew trees in our climate or this might not have ended well. (Yew does reportedly taste much better than most poisonous plants, which is why animals are sometimes found dead beneath yew trees with needles in their mouths.)
Anyone planning to harvest conifers as an herb or for food should become familiar with the differences between a fir and a yew tree. Here is a video that should help.
Some pine species also contain substances that are harmful to other animals. Ponderosa pine is significantly toxic to livestock and other species can cause sickness in dogs and cats. However, chocolate is also toxic to dogs and unhealthy for cats. So they just need different holiday treats.
For humans the needles of pine, particularly white pine, are a good source of vitamins and immune-boosting compounds. While the needles are best for eating when young and tender in the spring, they will release a significant amount of vitamin C and other immune boosting compounds even from tough, frozen winter needles.
Pine needles can be brewed into a pleasant tea that provides vitamins and acts as a decongestant for coughs and colds. For more serious congestion, it is possible to boil the needles down into a soup. And for a little boost, some people add them to spiced cookies.
While it is possible to dry needles and retain some of their medicinal effectiveness (as long as they are protected from sunlight while they are dried and stored), harvesting them fresh is no trouble at any time of the year in most places.
In the warmer months, pine trees can provide other essential medicines, primarily sap to cover cleaned, open wounds at risk of infection. Once a wound is thoroughly cleaned, coating it in pine sap is one of the best ways to ensure that it heals without infection. The disinfectant and protective properties of pine sap rival what modern medicine has to offer.