string user = "user";
string password = "password";
string ip = "ip";
string path = "/etc";        // Путь к папке
IZennoList foldersList = project.Lists["folders"];
using (SftpClient ftp = new SftpClient(ip, 22, user, password))
{
    try
    {
        ftp.Connect();
        var files = ftp.ListDirectory(path);
        ftp.Disconnect();
        foreach    (var file in files)
        {
            if (file.IsDirectory)
            {
                if (file.Name !="." && file.Name != "..")
                    foldersList.Add(file.Name.ToString());
            }
        }
    }
    catch (Exception e)
    {
        project.SendErrorToLog(e.Message, true);
        return null;
    }
}