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October
13, 2005
Hortiscope
Ronald C.
Smith, Horticulturist
NDSU Extension Service
Q: I have a question
about controlling weeds in my garden. I have grass sprouting up all over
the place in a bed of pinks and blue star creeper. Is there a spray for
getting rid of the grass without hurting the flowers? I have tried pulling
up the grass, but the runners have crept under the plants. I am a 12-year-old
amateur gardener. (e-mail reference)
A: There is a product
known as Vantage that is good at controlling grass in a garden setting.
See if your parents can locate some at a local garden store or a national
chain and have them apply it following label directions. It should do
the job for you.
Q: I have a cotoneaster
hedge that is infected with fireblight. I need to know if I have to cut
off the infected branches before I spray or if I can just spray (I purchased
streptomycin sulfate) to stop the blight from spreading. ( Kulm, N.D.)
A: Generally, spraying
now will do little good except to make you feel better. The active pathogen
already is there, so streptomycin cannot do anything at this point.
The infected branches can be cut back late this fall or early next spring
before leafing out begins. Spraying with a bactericide should take place
at blossom time to prevent infection. Repeating applications as new
growth takes place is strongly suggested through the summer, especially
if there is a hailstorm. Cutting now only would open new wounds for
the pathogen to enter and possibly stimulate new growth. If you have
other members of the rose family, such as crabapples and hawthorns,
they can be sprayed with the bactericide to prevent the disease from
becoming established. Be sure to follow label directions. Try to avoid
anything that will cause succulent growth, such as fertilization or
watering, because this type of growth is more susceptible to the pathogen
than hardened woody tissue.
Q: I saw one question
about where to get ornamental rhubarb. There is a list at www.plantea.com/rhubarb.htm.
(e-mail reference)
A: Thank you for
the listing. Our readers will appreciate having this source of information.
Q: I have planted
a row of bare-rooted, old-fashioned lilacs. I want to use the lilacs as
a border and a wind and snow fence, so I planted them around the edge
of my yard. I have a huge yard and I am in the middle of nowhere. Where
my yard is, I have a good feeling as to how the pioneers felt! (I hardly
have any trees in my yard, so the winters are a bear.) The lilacs only
are a foot or so tall. I have read they are a moderate growing plant and
should reach 20 feet in maturity. About how many years will it take them
to reach a decent height for blocking wind? How fast growing is moderate?
Will they be a good size 40 years from now when I won’t be able
to enjoy them? Any tips on getting them to grow fast and thick? (Kennedy,
Minn.)
A: Barring any calamity,
they should be their full size of 20 feet or more in much less than
the 40 years you have to retirement! Moderate means anywhere from a
foot to a foot and a half a year.
Q: We have a very
old and large chokecherry. What are the pruning guidelines? Can it or
should it be thinned out? If so, when is the best time? (e-mail reference)
A: Pruning is best
done in March when the tree still is dormant and the spread of disease
is minimized. It also facilitates healing of the pruning cuts faster
with spring growth coming on.
Prune to open the crown, but never leave any stubs. Always cut back
to a lateral branch or bud while attempting to maintain a natural size.
Survey the tree first before making any pruning cuts so you will know
when you have arrived at the last cut. In other words, know what you
want the finished product to look like before starting. Also, don’t
prune off more than a third of the total canopy at one time and don’t
expect something that looks like a sow’s ear to become a silk
purse the first year.
Q: I have a newly
constructed home with an existing hackberry tree on the property. To match
grade, the tree’s base was covered with 18 inches of black dirt.
Will this kill the tree or do I need to dig down and build a small retaining
wall around the tree base? (e-mail reference)
A: There is almost
a 100 percent guarantee that you will slowly kill the tree over the
next three to five years. Dig down to the original grade and out at
least to the drip line. That should help save the tree. Someday housing
contractors and horticulturists or arborists will get together and communicate
that covering tree roots above grade is akin to tying a plastic bag
over one’s head.
Q: I planted some
hydrangeas that are supposed to be hardy for my area. Should I do anything
special to them before winter arrives? (e-mail reference)
A: Yes, cut the
hydrangeas back to the ground. I do that to my hydrangeas every fall
using an old power mower. Do it after the hydrangeas have been frosted
several times, but before winter closes in. In your case, you probably
can use a chain saw or long-handled loppers to do the job.
Q: We just moved into
a house that has blueberry and raspberry bushes. When is a good time to
transplant the raspberry bushes? They are in the middle of a patch that
we need to rototill. How should I move them? Is it safe to transplant
them close to a building? Can I plant the raspberry and blueberry bushes
together? How long before the blueberry bushes provide fruit? What is
the best way to maintain these bushes? (e-mail reference)
A: Don’t worry
about your raspberry bushes that are in the way. Dig up the bushes and,
if you want to try now, replant them where you want, but they likely
will die at this time of year. Raspberries are very generous at multiplying.
In the spring before they leaf out, dig up a crown and divide it and
then plant where you want. Always cut back the canes that bore fruit
the previous year. Cut the canes to the ground, if it wasn’t done
the fall before. It’s a bad idea to mix the two species of plants
because they have different requirements and growth habits. Blueberries
require soil acidification on a regular basis with aluminum sulfate
and lots of sphagnum peat moss. It wouldn’t hurt the raspberries,
but I’m afraid that they would simply take advantage of the extra
care and grow like Jack’s beanstalk! They are challenging enough
to control without giving them extra encouragement.
Q: My husband was
given a flowering crab by his students when he retired last June. It appears
to be growing well, but has not blossomed. Is there a period they must
grow before blossoming or could there be a problem with this tree? (e-mail
reference)
A: Be patient and
give it another year or two. It will flower, so don’t worry.
Q: I usually put about
two drops of Liquid Miracle-Gro plant food in the water before I water
my plants. I am afraid of overwatering. When I bought a new bottle, it
didn’t say that it had chelated iron. Is this something important
for the plant? My new bottle doesn’t have it. (e-mail reference)
A: Miracle-Gro fertilizer
tends to acidify the soil somewhat, which makes the iron available to
the plant. Most potting soil brands have enough iron within to sustain
most houseplants. If the plant needs iron, it will tell you with interveinal
chlorosis on the most recent growth. It easily is corrected at that
time.
Q: We recently planted
a weeping birch in our front yard. It’s been in the ground for more
than two months and was doing very well until a couple of weeks ago. I
noticed that some of the leaves were turning yellow. I watered the tree
thoroughly. We returned home after the long weekend to notice that there
were more yellow leaves than when we left. I think I may have overwatered
the tree. There has been very little rainfall in our immediate area, so
I thought it could do with a couple of real good waterings. Do you think
I’ve overdone it? If so, what should I do to help it along? It’s
a beautiful young tree and we don’t want to lose it. (e-mail reference)
A: I’m willing
to bet that you have the tree planted too deeply. The crown (where the
stem meets the rootball mass) should be at ground level, not lower.
As little as 6 inches deeper can cause what you describe. Heavy watering
only exacerbates the problem. Pull some of the soil from the rootball
back to the surrounding soil level. If this is not the problem, then
I am at a loss to help you.
Q: How can I get rid
of potato bugs? No matter what kind of spray I use, I can’t get
rid of them. The bugs I have (I think) are called Colorado potato beetles.
(e-mail reference)
A: The larval stage
of the potato beetle will be the most vulnerable to Bt, which is an
organically approved material. When sprayed on the foliage and eaten,
it will cause the insect, at this stage, to become sick and die. This
will interrupt the reproductive cycle. Application after a rain event
is necessary and any new growth would require a reapplication. Reapplication
is needed throughout the season as the bacterial material breaks down
in the sunlight. I have found that the combination of hand picking and
spraying with Bt formulations is the most effective at controlling this
pest.
Q: Last year we planted
an endless summer hydrangea on the north side of our house. It was a very
nice, healthy plant, but no blooms. We decided to wait until this summer
to see if it would bloom. To date, it’s a nice looking plant, but
no sign of flower buds. The Annabelles next to it are doing fine. Does
the endless summer need more sunlight? Does it bloom on new wood like
the Annabelles? Any tips would be appreciated. Thanks! (Baudette, Minn.)
A: Endless summer
has the advantage of being able to bloom on old and new wood, so pruning
is not a problem. My guess is that it needs a little more time to mature
and then bloom. I hope you are not fertilizing it with a high nitrogen
material because that could inhibit blooming somewhat. Be patient. It
will get around to flowering for you.
Q: Our sump pump drains
water in our backyard. How much damage does drainage water do to lawns?
The other option is to have it run out the front, but then we have water
in front of the driveway. Any ideas? We just moved, so moving is not an
option! (e-mail reference)
A: Turfgrass is
a very tolerant to sump water, so simply move the hose around to keep
one spot from getting all the water. Whatever you do, don’t have
the water go down the front of your driveway. It looks tacky and encourages
algae growth, which is slippery and unattractive. You live in too nice
a neighborhood and you are too cultured to do such a base thing as discharging
sump water down the front of your driveway! Future generations of homeowners,
I am sure, will view our unsophisticated handling of sump water with
disgust - perhaps in the same manner we view the old European method
of discharging garbage and sewage into the streets.
Q: Someone told me
that silver maples are notorious for clogging septic drain fields. Is
that true? How close is too close? Should I move a couple of silver maples
that are within about 20 feet of my drain field? Any recommendations for
better trees near a drain field? (Grand Forks, N.D.)
A: Silver maples
get a bad rap for too many problems. What tree wouldn’t invade
a septic drain field with its roots? It is like putting freshly baked
chocolate chip cookies in front of a kid (or salivating adult) and saying
“don’t touch!” Definitely move them to about double
the distance. Another solution is to install a biobarrier around the
drain field to keep roots from penetrating. Don’t give up on your
silver maples yet because they grow fast, which everybody wants. They
also have nice fall color and are handsome trees, if allowed to mature
with proper care and pruning.
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Source: Ron
Smith, (701) 231-8161, ronsmith@ndsuext.nodak.edu
Editor: Rich Mattern, (701) 231-6136, richard.mattern@ndsu.nodak.edu
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