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June
10, 2004
Hortiscope
Ronald C.
Smith, Horticulturist
NDSU Extension Service
NOTE: Ron
Smith is on vacation for two weeks and the following responses are from
Joe Zeleznik, Extension forester and Todd Weinmann, Cass County Extension
agent.
Q: I have a poplar
tree that is approximately 20-years-old. From previous experience, I have
found that they rot from the inside. Can you tell me how to check if it
is rotted without cutting it down? Some of the bark looks like it is no
longer snug against the tree. (e-mail reference)
A: One way to find
out if a tree is hollow is to thump it with a rubber mallet. Another
method is to use an increment borer which drills into the tree, taking
out a core. This will tell you if the tree is hollow, solid or solid
but rotting. A regular drill with a small bit would work too. As you
go into the tree, if the center is hollow or rotten, you'll feel a change
in resistance to the drill. Just remember to use a small bit. Trees
can recover from small wounds pretty quickly. (JZ)
Q: I have a lilac
that is four years old. It only has a few flowers even though it sits
in full sun. This spring I found a dead branch. If I have borers, how
will I know and what can I do about it? (e-mail reference)
A: If the trees
do have borers, you'll see a tunnel entrance at the base of the tree
or maybe at the base of the branch that died. There will be sawdust
at the tunnel entrance. Tunnel entrances are about a quarter inch in
diameter. Permethrin and lindane are two insecticides that are labeled
for ash/lilac borers here in North Dakota, but the labels might be different
in your state. Check with your local nursery or with your Extension
agent to find out for sure. Good luck! (JZ)
Q: My son Michael
lives in West Fargo and has asked me which lilacs would grow best for
him. As far as I know, he plans to put them on the east side of his house
along a wooden fence that faces the street. (Minot, N.D.)
A: There are a variety
of lilacs that perform well in this area. Some your son may want to
try include: common lilac (Syringa vulgaris), late lilac (Syringa villosa),
copper curls lilac (Syringa pekinensis SunDak, an NDSU release) or ivory
silk lilac (Syringa reticulata Ivory Silk).
The city forester
of West Fargo, Yvette Gehrke, may have some other suggestions. She can
be reached at: ygehrkewfcity@aol.com
(JZ)
Q: The soil in my
subdivision is clay with a fairly balanced pH. About four years ago, I
planted a maple intending for it to become my large front yard centerpiece.
It is has not grown very much since planting. Its branches don’t
seem to be spreading and its leaves never make it to fall. During the
hot part of summer, the leaves develop a brown fringe that looks like
they are dry, but remain supple to the touch. Eventually the brown fringe
creeps inward until the leaves drop. I water it regularly. Is there a
fertilizer I can use? (e-mail reference)
A: Leaf scorch has
a lot of causes. The basic problem is that the roots can't get enough
water to the leaves. Some of the causes include highly saline soils,
flood or drought, soil compaction, nearby excavation, root rot, severe
temperatures, limited room for root growth and transplanting. It may
be starting with a mid-summer drying of the soils, but you respond to
that by watering. Are you over-watering? Clay soils tend to hold water
really tightly, but when they get waterlogged, then there's no oxygen
available to the roots. You said that the soils have a fairly balanced
pH; but what about salts? Is there salt in the water that you use for
irrigation? Because you live in a new subdivision, I'm curious about
the soil used in your yard. Sometimes, builders will strip the topsoil
away and sell it, then come back and just put a thin layer of sod back
down. This leaves poor subsoil to grow trees. Also, when trees have
been recently transplanted it takes them a few years to adjust to the
new site, approximately one year for each inch of caliper (diameter
at ground line). (JZ)
Q: I have a question
for you on planting Alberta blue spruce. I recently purchased two of them
from a garden store. They are five to six feet tall with a two year warranty.
I followed the instructions that came with the tree. Each pot is about
a foot and a half to two feet in diameter. I dug a hole adding another
foot and a half on the radius of the pot, which translates into holes
approximately five to six feet in diameter. I dug down just a little over
the depth of the pot. Because we have a lot of compacted clay on our property,
I mixed in about five bags of the recommended soil for each tree. I compacted
the soil around the root ball of both trees. I left about two to three
inches extra height for the level of the trunk of the tree. I was told
not to plant below the level of the soil otherwise the trees would suffocate
and die. I planted them just over a month ago and have been giving them
plenty of water when it doesn’t rain. They told me I should water
them until November. I planted them the second week in April. Is there
anything else I should be doing? (e-mail reference)
A: It sounds good,
but I would stop watering. Watering is crucial on the first day or two
after planting, but then you can cut back. The soil usually has enough
water for trees and constantly watering can lead to several problems.
The soil becomes too wet and the roots get no oxygen, fungal diseases
can become more common and the tree doesn't develop a wide-spreading
root system, instead it will only form roots where there is easily-available
water. If you're in the middle of a dry spell, then add additional water
about every 10 days. Regarding planting depth, I’m not quite sure
what you meant by “leaving about two to three inches height extra
for the level of the trunk of the tree, as I was told not to plant this
below the level of the soil otherwise the trees would suffocate and
die." The first big flare root should be just below the surface
of the soil. Planting too deep is one of the biggest causes of tree
failure. (JZ)
Q: Three years ago,
I bought two moonglow junipers that had been sculpted in pretty corkscrew
forms. Of course, for the pretty shapes I paid a pretty price. They were
approximately four feet tall when purchased and are probably five feet
tall now. They’ve done well, although they haven't grown much. We’ve
changed our original landscape plans so we'd like to move them. Is it
feasible to hand dig them? If it’s too risky, we could hire someone
with a tree spade to come in and do it for us. Would it be possible to
pot them in large containers instead of putting them into the ground?
(e-mail reference)
A: The most challenging
thing about transplanting trees is minimizing root damage and root loss.
When you pick up a tree to move it, either by hand or with a tree spade,
you lose a good part of the root system, sometimes as much as 90 percent!
Since these trees have been in the ground for three years, they're probably
just adjusting to the site and have expanded their root systems well
into the native soil. Root systems of established trees can be spread
as far as one and a half to two times the height of the tree. So whether
you dig by hand or use a tree spade, there will still be a lot of roots
lost. And it will take about a year of recovery time for each inch of
tree caliper (diameter at ground line). Be aware of these issues when
you make your decision. If you decide to put them in large containers,
they will require a lot of watering. (JZ)
Q: My yard was overgrown
with mature trees, so I decided to kill the weakest looking one which
was an old crab apple. Last fall I took down the branches leaving the
tree seven feet tall. This spring, much to my surprise, the tree flowered
on the few remaining small branches. I used a chain saw to girdle the
tree about a quarter to a half inch deep all the way around the base.
The poor thing has much more of a zest for life than I ever realized.
Do you have a way that I can completely put it out of its misery without
removing it or getting scads of suckers in my yard? (e-mail reference)
A: The key is killing
the roots. By girdling the tree, you cut off any source of food the
roots might have had from the top. Unfortunately, you also signaled
that the top was dead and they should send up some suckers. My guess
is that suckers will arrive in full force in a few weeks. All is not
lost however. You're going to have to go with some chemicals here. There
are a couple that should work pretty well, including Roundup or maybe
some others. Check with your local garden shop to see what they have.
You can get this to the root system by either spraying the new suckers
when they come up or by painting the chemical into the girdle. Hopefully
the tree isn't quite dead at the girdle yet, because you still need
part of the vascular system to be alive to translocate the chemical
to the roots. Be careful to avoid spray drift. (JZ)
Q: One of my cottonwood
trees is slow to leaf out and some branches appear dead. I'm sure it must
have some type of insect and I don't want my other cottonwood trees infected.
Should I cut the tree down? (e-mail reference)
A: Wait! There are
many reasons that a tree is slow to leaf out. Yes, it could be insects
or disease, but it could also be environmental damage. Get a proper
diagnosis before doing anything. You wouldn't want to spray for insects
if the problem was a fungus. You can decide what to do after a proper
diagnosis. If it is an insect or disease, then removing the tree is
definitely an option. But it's not the only option. Trees are pretty
resilient. Give it a few weeks and see how its doing before you decide
anything. (JZ)
Q: We would like to
build a fence between our house and the neighbor's. Their house is built
on a second lot which used to be the yard for our house. There is a beautiful
large lilac bush planted right in the middle of the property line where
the fence needs to go. Can we dig it up and split it between the neighbors
and us and then transplant it? I'm doubtful that will work because the
lilac is old and large. My husband thinks we can trim through the middle
of the shrub and put the fence right through the center. When would it
be best to undertake either suggestion? (e-mail reference)
A: The best choice
would be to trim through the center. If you trim back the lilacs to
four to six inches of stem just above ground line, they should send
up new suckers without any problem. To ensure the maximum amount of
suckering, cut them back in late winter or early spring. For the least
amount of suckering, trim them back in mid-to-late summer. You could
try digging up the bush and transplanting it, but if it's big and old
it would probably be incredibly difficult. Transplanting it would remove
a large part of the root system. That’s a huge stress on any plant.
It can be done, but it would take a lot of care and it would take several
years for it to recover and adjust to its new site. If you decide to
go this route, do it in early spring before the leaves come out. (JZ)
Q: My apple tree didn't
leaf out this year. How do you tell if it’s dead? Last year we had
our best crop ever, but not even a leaf this year. Some rabbits ate at
the bark on the trunk. Is that what caused this? (e-mail reference)
A: No new leaves
is not necessarily a good sign, but all hope is not lost. There are
several things that come to mind. A heavy fruit crop means that the
tree put a whole lot of energy into reproduction last year and may not
have put much into storage. Stored energy is where this year's leaves
and twigs will come from. Wait a few weeks and see what happens. On
the other hand, sometimes when trees put all their energy into reproduction,
it's a sign that they're dying and this is one last attempt to reproduce
before they die. Again, wait a few weeks and see what happens. How much
rabbit damage is there? I'm guessing they went all the way down to the
wood. By doing that they eat through the phloem and cambium, which are
two very important plant tissues. If they went all the way around the
tree, girdling it, then the tree will die. If they only went part of
the way, the tree might be okay. A rough rule-of-thumb for girdling
is that if less than a third is damaged, the tree should be able to
recover, if there aren't any additional stresses. If a third to a half
is damaged, it's really a coin-toss as to whether the tree will survive
or not. If more than half is damaged, the tree is a goner. Even a girdled
tree should leaf out and may take a year or more to die, so I doubt
that the rabbit damage explains the lack of leafing. (JZ)
Do you have a gardening
or houseplant question? Write to Hortiscope, Box 5051, NDSU Extension
Service, Fargo, ND 58105 or e-mail to Ron Smith at ronsmith@ndsuext.nodak.edu.
Note to e-mail correspondents: please identify your location (city and
state) for most accurate recommendations.
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Source:
Joe Zeleznik, (701) 231-8143, joseph.zeleznik@ndsu.nodak.edu
Source: Todd Weinmann, (701) 241-5707, tweinman@ndsuext.nodak.edu
Editor: Rich Mattern, (701) 231-6136, richard.mattern@ndsu.nodak.edu
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