Passing all test cases but exceeding time limit (~5 sec runtime) in a few. Could someone suggest an alternative approach or improvements to my current solution (C#)?

    public static int poisonousPlants(List<int> p)
    {
        int days = 0;
        List<int> plants = p.ToList();
        bool finalDay = false;
        do
        {
            int pCount = p.Count;
            for (int i = 1; i < pCount; i++)
            {
                if (p[i - 1] < p[i]) plants.RemoveAt(i - (pCount - plants.Count));
                if (i == pCount - 1)
                {
                    if (p.SequenceEqual(plants)) finalDay = true;
                    else days++; p = plants.ToList();
                }
            }
        } while (!finalDay && p.Count > 1);
        return days;
    }