I planted 105 plants as a border on coast of Maine and 90 percent died over winter. They're in full sun on a south slope, though a lot of water does run down slope to ocean. They're well fertilized and mulched with 3 inches of bark mulch, in Zone 5. They were planted in spring, and all were flourishing all summer. Any thoughts?
Dwarf Fountain Grass Hameln
Certified GKH Gardening Expert
There are a couple of things that could have caused this. The first is that most of the country had a pretty cold winter. If this was true for your area, it may have been just too cold.
The second is plants in areas that may stay wet in the winter are more susceptible to cold damage due to the fact that the water may freeze and unfreeze all winter. This sort of temperature action is very damaging to the roots. If you suspect this, the best way to handle it in the future is to provide extra protection, usually through mulch, to keep the soil an even temp. In some areas, they will even bury plants in snow as snow, believe it or not, is an excellent insulator and will keep the plants at an even temp, reducing the damage to them from fluctuating temps.
The third would be that in the winter, the fresh water in the form of rain may have been tied up in frozen form (i.e. snow) so the salt levels in the soil become more concentrated. I think this is less likely, but possible.