Pine trees in the home landscape over time will lay down a thick duff layer of needles. For some homeowners this becomes a problem when the lawn beneath the tree dies.
Graceful and stately, our much-loved native white pine (Pinus strobus) becomes a canopy tree with a bare lower trunk and, in a home landscape, the question then arises of what to grow under it. Raking up all the needles and liming the ground to reduce acidity in an attempt to reestablish the lawn will just harm the pine. Adult white pines have established a symbiotic relationship with soil fungi and that relationship is disturbed if the homeowner forces a change in the soil chemistry. It can kill the tree. White pines have evolved to grow with a carpet of their own needles beneath them.
Sometimes a homeowner inherits an overgrown Scots pine (Pinus sylvestris) from a previous landscaping effort. Scots pines are the common Christmas tree pine. For the Christmas trade they are pruned to thicken them up. Left to their own devices, they are straggly trees. That straggliness can become picturesque in age. While I don’t recommend planting Scots pine for landscaping, there may be good reasons to keep Scots pines that have achieved some height or some picturesque ruggedness. Again, the homeowner has a carpet of pine needles and questions about what can be planted under the pine.
Leaving the needles undisturbed except for weeding is a fine choice in many situations. It is easy and the needles form a pleasing fine textured mulch. White pine needles are soft enough they can be walked upon with bare feet. Still, in smaller yards, homeowners with the urge to garden may resent the space given over to nothing but needles. There is an understandable desire to grow something handsome and interesting in that space.
When you recast the needle mulch from a problem to an opportunity to grow those plants which are naturally to be found under pines in the forest, you quickly realize how valuable those needles are. That acidic mulch, with its associate fungi, creates the ideal soil conditions for some fine plants.
There are at least two lovely evergreen ground covers that seem to specialize in growing under pines: shinleaf (Pyrola spp.) and pipsissewa (Chimaphila umbellata).
Pipsissewa makes a lovely glossy evergreen carpet. Because it grows in acid conditions, I have often seen it growing in cottage country and so I assumed it liked cool north-woods conditions. Then I saw it growing with extraordinary vigour in a played-out sand pit that had been planted decades ago with Scots pine. This is a blazing hot and droughty site, and the pines are not even native. The only thing this site has in common with the places I had formerly seen pipsissewa is the deep carpet of pine needles. Emboldened by this observation, I tried growing pipsissewa under a large white pine in a suburban yard, with some success.
Pipsissewa seed is dust fine, I assume that, like orchid seeds, the seed needs to make a symbiotic relationship with an appropriate soil fungus very early in the sprouting process. The New England Wild flower Society’s William Callina, who seems to have successfully germinated almost everything, says in Growing and Propagating Wildflowers, that he has never succeeeded with pipsissewa. While mass collecting from the wild is never ecologically responsible, this might be one plant which needs to be vegetatively propagated to get stock plants started. If you carefully collect a small number of rooted offsets from an abundant wild supply and plant them in the deepest and oldest (least disturbed) part of your pine needle duff and water them in with rain water, not tap water, there is a reasonable chance you can successfully establish a few plants, from which you can take offsets in subsequent years. I used the old sand pit, which had acres of pipsissewa as my supply, and established five little plants of under the garden pine. We weeded the wild raspberry and hawkweeds which pushed in at the edges of the needle duff, and the little pipsissewas are spreading handsomely.