Growing Concerns 605: White pine, topping, root rot


You should admire a tree's graceful sway but never "top " it


Dear Janet,

In front of my house are two large white pines that are a few feet from each other. However, the trees are also about 15-20 feet above the corner of the roof. They really sway in the wind, which is a good thing and part of their charm. But I am concerned about their height, which is taller than our three-story house.

Is there a need to cap them -- cut off the tops? Will this hurt them in any way? Should I prune the dead branches at the bottom? These trees really bend in the wind and the higher they get the more concerned I am.


 Dear A.S.,

Cutting through a trunk or major limb to shorten it -- called topping -- is one of the surest ways to weaken a tree. Any arborist worth his or her salt tops a tree only as a last resort.

There is a rot-resistant zone of defense at the base of every tree limb, where it attaches to a trunk or larger branch. It's there in the lower limbs of your pines, which probably died in the trees' own shade. Fungi and insects may now be decomposing that wood but will be stopped at the point of branch-trunk attachment. So the trunk is not damaged in the tree's natural shedding process.

If we cut properly to leave intact the collar at the base of a limb, the defensive zone is preserved. We can remove even large limbs yet know that any decay that enters the branch stub will probably be barred from the trunk. The remainder of the tree will remain sound. 

The barriers to rot are much weaker within the column of wood that constitutes one trunk or large branch. To cut across a woody trunk is to open the entire unit to decay that will probably descend all the way to the base of the tree in a column the width of the cut.

Healthy wood in a tree is capable of withstanding enormous pressure. It bends in the wind and under weight of snow or ice, then rebounds. But decayed wood doesn't bend. It snaps.

A tree of a type that will grow too large for its site can be kept small by annual pruning. But the time to cut is when the parts to be pruned are new, before they become woody. Or to cut every year or two so the tree never develops much wood and weight beyond the unavoidable topping cuts. The greater the difference between the tree's natural size and our wishes, and the faster its growth rate, the bigger the job to keep it small.

Trees are more stable when they have sound wood but a wide, healthy root system is equally important. We can never declare a tree absolutely safe from breaking but some are more hazardous than others. A certified arborist can examine your site, the trees' wood and roots, and give you the specific recommendation you need. That may be to remove the trees but certainly not to top them.

 Short report

Learn what to do by checking a struggling shamrock's roots.

E.C. is concerned that a shamrock plant which grew very well all last summer has been failing since being repotted by a florist.

 Florist's shamrocks (Oxalis) go through a dormancy each year. That may be what's happening, in which case E.C should stop watering. A plant without leaves has very low water needs but can rot from too much moisture.

Whenever a potted plant puzzles us with sudden leaf loss, it's a good idea to slide the plant out of its pot and inspect the roots. Root tips can die from cold or the airlessness of water logged soil. Once dead, they rot. 

Rotted roots are as easy to spot as bad vegetables in a crisper drawer. Firm, light colored roots are normal. Mushy brown tips are not, so clip them off, let the root ball drain if it's very wet, then put the plant back in its pot. Move it into very good light, where the remaining leaves can harness enough solar energy to repair and replace the lost roots.

If  you see only firm root tips and solid tubers like radishes when you de-pot your shamrock, E.C., then all is still well. Hold off watering except to keep the soil from going absolutely dry. Wait for the new growth that will come once the plant has completed its rest.


I enjoy answering questions you mail to me or post on my school's website. However, some problems have no solution. Don't expect much help from me if you pose a "stumper" such as: I talk to my plants all the time while I tend them. Why do they only talk back, by making their wishes or needs pop into my head, in the middle of the night or when I'm far away?


Green thumbs up

to this winter's MSU Extension Master Gardener candidates, now beginning their classes all across the State. When you share what you learn with others through your required volunteer hours it will add up to tens of thousands of hours of helping each year. Now that's truly an "extension" of information!


Green thumbs down

 to the search for hardy perennials that bloom all season. A perennial's nature is to spend part of each year storing energy for the future, taking a rest from flower production as it does this. Accept and enjoy perennial gardens for what they do best, which is to change throughout the growing months, offer contrasts in plant form and texture, and extend the flowering year into April and October where annuals can't go.

 Originally published 2/12/05