White Pines

My last couple of posts were about school and I hope my advice helped you get off to a good start. For this blog post I return to discussing trees and how you can help your trees survive. Let's talk about White Pine. White pine (Pinus strobus) has an interesting distinction in my life. It is one of my favorite trees to see in it’s natural state and, unfortunately, it is also the number one tree that I am asked to look at in a landscape setting. The fall planting season is in full swing and if you are planning on using eastern white pine, be sure that white pine is suitable for your site and that your landscape professional has a good source for healthy trees. Site selection, source selection and proper planting will ensure a good start for your trees. Like I said, I am a fan of White Pine but this month I will discuss the problems associated with this species and management strategies to keep your white pines healthy.

White pine is a native forest species that in the ornamental landscape is faced with many cultural problems. You may often hear the words “white pine decline”.  White pine decline refers to a combination of environmental stress factors, insects and soil pathogens.  White pines are sensitive to heat, soil pH and the compacted soil common in landscapes.  One problem is that the white pines available from nurseries have been grown originally from seeds.  Due to the natural genetic variability found in seed grown trees, individual white pines will differ greatly in their adaptability to landscape conditions.  In other words, a planting of white pines, all from the same nursery, will frequently have some trees declining and the rest doing well.

Declining trees usually look a paler green, or even yellowish, compared to healthy trees. Needles often are shorter than normal. Needles from the previous season often drop prematurely, giving the tree a tufted appearance. With the loss of needles, the tree has reduced it’s ability to produce the energy it needs to survive and this will lead to tree decline. Decline may be gradual or rapid, depending on the type and severity of the stress factors and the overall health of the tree. Do not mistake annual needle drop for white pine decline. It is normal for conifers to drop their oldest needles in the fall. This annual shedding occurs on all trees at about the same time, and always occurs in the fall. An abnormal needle drop would occur in the spring or summer, affecting only one or a few trees, rather than all or most of them. 

White pine decline in landscapes has been the subject of several recent research projects.  This reaseach has determined that summer temperatures above 75° F, salt spray, and unhealthy soils (poor drainage) are serious stresses on white pine.  In addition, white pine is subject to a greater array of diseases than any other North American tree species.  White pine root decline is often associated in the death of weakened pines. 

With all this bad news, how can you keep your White pines healthy? First, call an Arborist to check on your trees before they start to look bad; a variety of problems can be addressed if caught early enough.  Properly mulching around white pines and watering deeply once a week during hot spells is recommended.  A fertilization and pest control program should also be established. Soil pH should be maintained between 5.2 and 5.6 and micronutrient deficiencies (such as iron) should be corrected. Soil compaction can be addressed with a variety of soil aerification procedures such as root collar excavations or a Root Invigoration Program. When planting white pines avoid low spots so that trees are not standing in water after heavy rains and plant in an area that has good drainage. Don't plant on sites that have a high pH (greater than 7.0) or where the pines are exposed to splash from de-icing salt. Make sure the trees have plenty of space for root expansion, and plant where they are not in deep shade. This proactive approach to tree care is important, especially for white pine, because after decline starts it may be too late. Declining white pines will frequently die, even with the best of care.