I bought this mini pine a couple Christmases ago and noticed that it is actually a cluster of several stems/trunks. Should I divide the trees or leave them together?
Also, some of the limbs have some yellowing – what caused this and should I prune off the entire limb, trim off the yellow parts or leave it alone?
Thank you for including a photo here. That helps me understand your plant situation and provide insights into potential problems that you are unaware of.
It is a common practice to grow multiple plants together in a single pot. The reason is to create an overall fuller, more compact looking plant. It is done deliberately by the nursery growers and there is rarely a good reason to separate these plants with roots that are completely intertwined. Trying to divide them often results in the deterioration of the divisions as the roots are traumatized. In addition, few people know how to divide plants properly. The individual plants do NOT compete with one another. So, leave them together.
The yellowing of lower branches is not unusual. It is to be expected as new branches are added on top. However, excessive yellowing can be caused by improper watering and/or light.
My observation is that your Norfolk Island Pine is in a pot that is much larger than it should be for maximum growth and proper watering. It is a common practice to move plants to larger pots on the mistaken notion that plants grow faster when they are in larger pots. In fact, plant growth is maximized when the plant is kept moderately potbound. The danger of over-potting is that the excess soil retains water for too long and causes the roots to slowly and invisibly rot. That may be contributing to the lower branch yellowing that you have observed.
Unless you repotted within the last couple of months, it is probably best to leave it in its existing pot. However, you should remove all soil you added to the top of the original rootball. Removing this excess soil will help speed the drying process. Then, allow the top inch of soil to become quite dry before adding any water. Add just enough water so that it reaches that same level of dryness again in about a week. You will have to experiment and adjust the amount of water accordingly.
If you recently repotted and the original rootball is still intact, then you can remove all of the soil you added and put the original rootball back into the original pot or one that is the same size as the original. If you don’t like the appearance of the original nursery pot, then place it inside a decorative planter of your choice. Double-potting works very well; repotting rarely does.
Your NIP should be very close to a window indoors so it gets plenty of light. If you have it outside when temps are above 40 degrees F., then it should be in light shade and protected from any direct outdoor sunlight.