I started growing a giant sequoia from seeds a little less than two years ago. Since then one of them has grown to a size of about 17cm tall. First I had two of them but at one point the branches started turning grey and dying. We managed to save one of them by cutting the greying branches off. But it has battled with dying branches ever since. It is in a large pot with good drainage so I don't know what the problem is. Any help?