Ask the Steward
By Dan Ernst
There is a row of 12’ tall white pine trees along the road in front of my house that are turning brown on one side. This happens every winter. What is happening?
There are two forces teaming up to cause this late winter browning of White pine trees. First, and probably the most significant is road salt. White pine needles are especially sensitive to salt kicked up as cars and traffic rush past. This fine mist drifts over to the pines and lands on the needles coating them with a thin layer of salt. The salt pulls moisture from the needles causing them to dry and brown. You have probably observed this browning to be most noticeable on the side of the trees facing to roadway.
To the salt affect add the winter winds. These dry winds are hard on the thin needles of White pine trees- especially those already dealing with drying salts. The steady cold, dry winds during times of low winter root activity depletes needle moisture faster than the roots can replenish.
In most cases the trees may lose some needles, but the trees will usually survive and green up in the spring and summer. The salt will eventually be washed from the needles and leached through the soil by winter and spring rains. Only in the case of salt spills or heavy build-up are the trees in real jeopardy.
How weed free do I need to keep my new (2 year-old) tree plantation? When is the best time to mow and still protect wildlife?
There are mixed opinions on this one. However, in most plantings it is crucial to provide a relatively weed free area three to four feet around your young trees for 2-4 years after planting – sometimes longer in extreme conditions. But, the trees do not need to be weed free all year long. If you can have a relatively weed free zone around the trees for 3 months (May-June-July) the planting should do well provided the right trees were planted, on the right site, and in the right way. After July the trees cease most top growth and start storing energy in their roots for next year.
Concerning mowing- if you have good weed control strips or spots around your trees you may not need to mow at all. However, mowing may be helpful and desirable if you are concerned about the appearance of the plantation or have an overabundance of rodents (or rabbits). Mowing is recommended in many plantations 1-2 times per year (e.g. July 15 and Sept 15) so you can easily find the tree rows again next year. Do not worry about late season weed growth close to the new trees. Mowing a foot or two away from the trees may help hide them from the deer who just love those tasty buds in late winter and early spring.
Wildlife biologists recommend avoiding mowing between March 1st and July 15th. This is the primary nesting season for wildlife. If you must mow during this period consider raising the mower deck to leave at least 8" of growth.
Dan Ernst is an Assistant State Forester with the Indiana Division of Forestry. He oversees the state forests in Indiana and has authored the “Ask the Steward” column for years. Have a question for the column? Email Dan at firstname.lastname@example.org.