Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
4/23/01
Contacts:
Jeff Iles, Horticulture Extension, (515) 294-0029, iles@iastate.edu
Elaine Edwards, Continuing Education and Communication
Services, (515) 294-5168, eedwards@iastate.edu
Yard and Garden Column for the Week Beginning April 27
Usher in Spring with the Plant Guy
By Jeff Iles
Extension horticulturist
Iowa State University Extension
Hey, Plant Guy:
Help! I think my tree is bleeding to death! Here's all the
gory details. Last Saturday I grabbed my new pruning saw
and ventured out in the yard to do a little spring tree
surgery. Job one was to rid my beautiful sugar maple of an
awkwardly-growing branch that had silently been mocking me
all winter. Left to its own devices, this troublesome
branch would surely impede the growth of neighboring
branches, and more importantly, would announce to the world
that I was a neglectful tree owner. Not on my watch Plant
Guy!
So, with great precision, I removed the offending limb
and was about to move on to the next task when, to my
horror, noticed an alarming amount of clear fluid welling
from the branch stub and running down the bark. After the
initial blood-letting, which went on for at least a couple
of hours, the flow stopped. But it periodically resumes all
by itself without any further wounding. Plant Guy, tell me
I haven't caused irreparable harm to my tree.
Sanguine in St. Anthony
Dear Sanguine:
O.K. You haven't caused irreparable harm to your sugar
maple. Instead, what you've been witnessing is the flow of
maple sap. Yes, the sap does contain sugar (plant food)
your tree manufactured for itself the previous growing
season, but the amount of stored carbohydrates lost is
really quite negligible and shouldn't harm your tree in the
least.
Actually, the physiology of sap flow in maple trees is an interesting story. Sap flow can occur anytime during the dormant season when air temperatures fluctuate above and below the freezing point. However, the largest flows take place in late winter and early spring. According to current theory, when temperatures fall below freezing and the sap in your maple tree freezes, negative pressure (suction) is created within the sapwood. This negative pressure causes water to move from the soil into your tree, thereby increasing sap volume. Then when temperatures rise above freezing, the frozen sap thaws and several forces act on the increased sap volume to create a positive pressure. Wound a tree with positive sap pressure and, voila, you can have a pretty dramatic sap flow event.
Sap flow, from a pruning wound for example, will continue as long as pressures inside the tree are greater than the outside atmospheric pressure. In fact, the period of sap flow can be highly variable; from a few (1 or 2) to several (15 to 20) hours in length. Repeating episodes of sap flow from the same wound can occur throughout early spring if temperatures continue to cycle above and below freezing.
Of course, sap flowing from pruning wounds can be avoided all together if you delay pruning maple trees until late spring or early summer. Remember, sap flow ceases entirely when the requisite temperature cycles end for the year.
Hey, Plant Guy:
I'm a member of our town's tree planting committee, and this
spring we're scheduled to receive 25 bare-root green ash
trees for our city park. Seems like a risky proposition to
me, shipping trees half-way across the country with their
roots hangin' out like that, but who am I to question such a
thing. Anyway, I've never planted a bare-root tree before,
so when I heard about a tree planting seminar offered by
some "expert" from the college, I knew I'd better be in the
front row.
But seriously Plant Guy, I'm not sure this so-called
expert actually knew his stuff. For example, after he
planted his bare-root tree he used a couple of stakes and
straps to keep it from blowing over. Everyone in the
audience knew that if he had just planted the tree deeper,
it wouldn't have needed staking, but we were polite and kept
our comments to ourselves. Anyway, I plan on telling
everyone on our tree planting committee to "plant deep" so
we won't have to go to the trouble of staking. What do you
think?
Planting Deep in Deep River
Dear Deep:
So, that was you in the front row. Anyway, one thing is for
certain. If you want to kill those newly planted trees, go
ahead and plant them deep. In fact, planting trees too deep
can cause trees to die within months of installation, or
lead to several chronic ailments (girdling roots, stem or
trunk rots, etc.) that ultimately result in tree death.
So how do you properly plant a bare-root tree? First, prepare a wide hole that will easily accommodate the tree's roots. Roots should never be twisted, bent or screwed into a "too small" planting hole. Next comes the all-important issue of planting hole depth. Basically, hole depth should allow the tree to be positioned so the root collar or trunk flare (swelling that connects roots with the main stem and indicates previous planting depth) is level with, or slightly higher than the surrounding grade. Some people like to build a firm, cone-shaped mound of soil at the bottom of the hole to help support the tree at the proper depth. Finally, backfill soil can be added and watered-in to eliminate undesirable air pockets.
Yes, staking may be necessary for newly-planted, bare-root trees, but they usually can be removed 6 to 12 months later. Planting deep just to avoid staking is a little bit like pushing your car off a cliff just to save gas money. See you at the next tree planting seminar.
Hey, Plant Guy:
I feel like I've just been kicked in the gut. Every morning
as I walk across the central campus of Iowa State
University, I pass beneath the branches of several huge, old
white pines located just east of the campanile. But this
morning I noticed one of the largest and probably most
striking specimen had been removed. Plant Guy, I've walked
by that tree for 20 years and have never noticed anything
wrong with it. Why would they take a tree down that was
perfectly healthy?
Ambushed in Ames
Dear Ambushed:
Like you, I'm saddened by the loss of this campus landmark.
For more than 100 years, the grand white pine you speak of
has sheltered members of the ISU community and visitors to
campus from sleet, snow and ear-numbing gales of winter, and
searing rays of the summer sun. Few would argue that on a
sweltering August afternoon, the cool oasis created by its
massive canopy was the best place to be on campus. But the
simple fact is, this white pine wasn't perfectly healthy.
In fact, so apparent were its flaws that the decision to
remove the tree was, in today's lexicon, a "no brainer."
Keep in mind that on a busy college campus, or anywhere people gather for that matter, it is the responsibility of the grounds maintenance professionals to ensure a safe environment for people and property. And fortunately for those of us that hustle by this white pine on a daily basis, an observant campus grounds employee noticed a longitudinal crack at the base of the tree that could be seen opening and closing during one of our recent windstorms. Strike one. Subsequently, core samples taken from the massive trunk revealed an alarming amount of decayed wood. Strike two. Finally, the trees location (6 feet from a busy sidewalk) and the risk it posed to pedestrians became strike three and led to the correct call. Remove the tree and do it fast!
But before we leave this topic, think for a moment about the person responsible for planting our fallen white pine. Wouldn't they be surprised to know how many people appreciated and benefited from the tree they planted so long ago? Or how many times "their tree" had served as background for some student's graduation picture? And if we were somehow able to speak to that person, wouldn't it be ironic if they told us how insignificant the memory of planting that tree was? Sound familiar? You know what? I think I'm going to plant a tree this weekend. No big deal.
ml: isugarden
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