I am trying to grow this Pennsylvania Sedge on a dry shady hill in my back yard. The hill leads from my house to a flat area that has large trees. The hill doesn't collect leaves that would normally collect around the plants in the woods. It was originally planted with fescue but the grass is slowly dying because of the shade and lack of water. It was suggested that I try Pennsylvania Sedge. The few plugs that I planted 2 years ago haven't thrived as I hoped. I would like to know if I need to fertilize them with a something like hollytone to give them a little nitrogen and lower the pH. The soil is clay.
Fairfax County Virginia
Carex tends to tolerate a wide range of pH levels (from 5 to 7 or an even wider range for some), so I don't think that is a problem unless there is something very unusual about the soil in your area. I recommend that you get a soil test for that area. Virginia Tech offers soils tests for small fee ($10 for VA residents) and you can pick up the boxes for free at your local Virginia Cooperative Extension office. You will need to mail the box to Virginia Tech directly.
Also another possibility could be that, if it is an area heavily traveled by animals (particularly deer and people), the Pennsylvania sedge (C. pensylvanica) is being trampled and damaged. Deer don't necessarily eat Carex, but they may use it for a resting area.
You don't say how large an area you have to cover, but if it is possible (and it isn't a large area), you may want to consider replanting the sedge in soil that has been amended with a generous amount of organic matter (namely compost or loam) for drainage.
If amending the soil isn't possible because it is a large area and the tree root amount is considerable, you may want to consider having the Fairfax County Master Gardeners pay your property a visit for a closer examination of the growing conditions in which your Carex is growing. If they can't visit your property (particularly because our current COVID-19 situation), you could also submit photos of the site (showing it as a whole) and photos of a detail of the soil and plants themselves (the Carex and the surrounding plants and trees) for better examination.
Here is the Fairfax Master Gardener webpage: https://fairfaxgardening.org/
Also, you can contact the Fairfax Virginia Cooperative Extension here for advice, information, and soil test boxes: https://www.fairfaxcounty.gov/parks/green-spring/master-gardeners
You should still be able to email and/or call their offices.
Have a Great Gardening Week,