Kalmia latifolia need well-draining acidic soil— the same kind of conditions that blueberries and rhododendrons like.
Mix tons of peat, sand, perlite, and pine bark mulch together in a basin. Soak it with the hose. Churn it with your hands to mix it well.
Put a 2-inch base layer of this mix on top your native soil. On top of that, place the transplanted mountain laurel rootball. Then add more of the mix around the mountain laurel. Do not bury the trunk deeply; it should be at the top of the berm you are making. Just put about a centimeter of mix on top of the rootball. Don’t put any mix right up against the trunk. The mix should be flush with the rootball— pack it in all around the rootball and outwards about two feet in each direction.
Then take a mix of both pine bark mulch AND nuggets and dump this on top and all around the planting about 4 inch deep. Then stand there with the hose and slowly SOAK the whole area.
Let the site dry out for a day. Then SOAK it again. Wait for it dry out… allow it to be dry for about a day, then SOAK it again. Do this for the first 2 months of its first transplant season.
Get a good plant that hasn’t been overfertilized. Balled and burlapped is better than potted. Most ideal to get from a reputable high-class nursery like Broken Arrow of Connecticut. They grow their plants in the right conditions without pushing them into a state of stress. I have had multiple mountain laurel transplants die on me when I did not follow these steps. This soil mix… and sourcing them from Broken Arrow… increased my instances of success. These plants do not transplant well otherwise.
Rather than full sun or full shade— mountain laurel seem to do best in part-shade.
Don’t fertilize heavily. Just throw on the occassional compost, kitchen scraps, pine bark mulch, Holly-tone, leaf litter, coffee grounds, bone-meal, or other light organic acid-lover ferts.
If the underlying soil pH creeps up too high, then you might need to gently apply soil acidifiers to bring it back down to an acceptable range. If the leaves turn yellow, then you’ll know this to become necessary.
Despite being native— mountain laurel have become strangers in their own land. There are only pockets of them left in the Poconos, northern Jersey, CT woodlands, PA coal country, Massachusetts, and spots in southern Appalachia. Not knowing how to care for them— people try to dig them out of the woods, often killing them (and in many jurisdictions, illegal). The seeds are microscopic and a hassle to germinate. The damn things are almost impossible to propogate from cuttings. Therefore, fewer and fewer nurseries will fool with them, and even fewer successfully.
That’s why they are expensive, and hard to find… but there is perhaps no plant native to the Eastern U.S. prettier than a mountain laurel in full bloom in May or June— heralding the start of summer. They are worth every penny and all the hassle. And once they are established, they can be long-lived. We must bring them back to our environs, and bolster their numbers. They bring the beholder so much joy and comfort.