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January
6, 2005
Hortiscope
Ronald C.
Smith, Horticulturist
NDSU Extension Service
Q: Some of the leaves
on my English ivy topiary are starting to turn yellow. It is still in
the plastic nursery pot it came in. Could that be the problem or what
could be causing it? I mist it weekly and water when needed.
(e-mail reference)
A: Try repotting
in a clay pot using the next nominal size larger pot. Use fresh potting
soil and move it to where it can get a little more natural or artificial
light. Check the leaves for possible spider mite damage, as they are
susceptible to this pest. A stippled yellowing and some very fine webbing
should be evident. Don’t overwater the plant. It is better to
grow it a little on the dry side. A regular misting regime, such as
once a week, will keep most spider mite infestations at bay.
Q: I know that nearly
every houseplant needs a resting or dormant period, when watering and
fertilizing frequency is reduced and the plant is placed in a cooler location
to help it through its rest period. How long should we allow for this
rest period before we put the plant back to its usual location and the
fertilizing and watering schedule resumed? (e-mail reference)
A: About 60 to 90
days, depending on the plant. Some are very sensitive to this regime,
others not. It requires observation skills on the part of the caretaker
to respond to the nuances of change that some plants go through.
Q: I have several
cottonwood trees I would like to remove. Three of them are next to electrical
boxes. The tree removal service I contacted will remove them but will
not grind the stumps. Is there anything that I can apply to the stumps
that will kill the root system? I can’t afford to have new sprouts
popping up. (e-mail reference)
A: Stump grinding
will not prevent the roots from sending up sucker growth. What you can
do is rent a stump grinder yourself from a local rental store. A material
called Salt Peter can be applied that will accelerate the death of the
stump and roots. You also can get a product known as Sucker Stopper
– RTU, which will prevent sucker growth from coming back.
Q: I just purchased
a schefflera plant at an on-clearance, green-thumb-wanted sale. Admittedly,
my green thumb is only the palest green and I don’t have much luck
with fussy house plants, but I thought I’d give it a shot. Four
days after bringing it home, a dark brown color appeared on one stem all
the way up to the leaves. The coloring is starting to encroach from the
stem connection out along the leaves. I wouldn’t think the store
(big-box home repair store) would have sold it if they suspected disease,
but one never knows. Could the problem be overwatering (was very wet when
I got it)? Why would that affect one stem and not the others? Could it
be a fungal infection? What should I do or is the plant doomed? (e-mail
reference)
A: Cut out the discolored
stem. It appears to be a spreading canker, and removing that stem would
solve the problem for the most part. Overwatering is the most common
houseplant problem. Water it only when the top inch is dry.
Q: Are Christmas cactus,
orchids and goldfish plants in a poisonous group? I have a few houseplants
I’m trying to keep away from my 18-month-old granddaughter. (e-mail
reference)
A: They are not
listed in any of my poisonous references, but I still wouldn’t
take a chance with any of them. You don’t want to be the first
to discover that one of these does have some poisonous factor that is
toxic to children. Most poisonings are reported in livestock, which
are larger than humans and therefore it takes more to kill them. Not
too many livestock have access to the plants you mentioned, so put the
plants out of the child’s reach to be on the safe side.
Q: What part of the
hollyhock is the seed? (e-mail reference)
A: The seed is in
the button that forms as the flower fades.
Q: I repotted a plant
that I expected to be root-bound, but was alarmed to see the roots extended
only a few inches, not even to half the depth of the pot. It’s a
plant that is more than a foot in circumference, but not leggy or compact.
Why would the roots be so shallow? (e-mail reference)
A: There are a number
of possibilities, such as lack of sufficient phosphorus, kept too wet,
too low a light intensity or duration, stratified soil or a combination
of problems. I suggest repotting with the appropriate soil, in a free-draining
container and placing it in a bright, indirect light location. Water
it moderately, allowing the soil surface to dry about an inch or so
before re-watering.
Q: I was in New York
city this summer and bought some really good, large, red grapes. I gave
some to a friend and she suggested that I save the seeds and plant them
next year. Can you tell me when is the best time to put the seeds in the
ground and how many years it would take to grow some grapes? (e-mail reference)
A: Having never
done this myself, I am depending on one of my research references. The
seeds need at least 60 days of temperature stratification to cause germination.
The data says the seeds will germinate best with light, rather than
darkness, so do not plant the seed deep. I would simply scatter the
seeds over a pre-moistened, sterile media and pat them gently into the
surface with the palm of your hand.
Q: I am a woodturner,
and often when turning a piece of box elder, there will be an area of
red coloring in the wood. Some have said it is caused by an infestation
of some sort. I don’t always find an obvious worm hole and often
the coloring seems to be brushed through the wood instead of concentrated,
like the coloration caused by the ambrosia beetle. (e-mail reference)
A: I would have
to guess that it is an infection, possibly benign, that shows up at
times and is compartmentalized by the tree’s defensive mechanisms.
Q: I received three
schefflera plants in one pot more than a year ago. Last summer I transferred
them to new pots. Immediately I saw new growth. Then dark brown-black
spots developed at the node of one of them. The spots moved up and slowly
killed the new growth that had developed. I cut off the discolored area,
but a black coloring started below in the healthy looking stem. The spots
eventually covered the whole plant. Now something similar is happening
to another plant. (e-mail reference)
A: The schefflera
(Brassaia spp.) plants are suffering from a stem canker fungus brought
on from the stress of repotting. Repotting often weakens the plant’s
various resistance mechanisms. The plants went through an abrupt change
from their “three-in-a-pot” environment to each one having
a container. Very likely the roots were damaged during the process of
transplanting, along with the likely fact that the plants were not all
that vigorous to begin with. If the visual symptoms of the canker already
have been noted on the remaining plant, you might as well throw it away.
If the symptoms are absent, then try to find a product called Fungicide
3 put out by the Schultz company. It is a neem tree product that is
safe to use on interior plants and also has insecticidal and miticidal
activity. Whatever you do, don’t try to push the plant by overwatering
or fertilizing. Try to locate it in as ideal an environment as you can
find in your home and monitor it carefully. New growth should appear
in a month or two, depending on its location to direct light.
Q: In the fall when
I dig up my tubers, I dig up the whole plant and then cut off the plant,
leaving about 2 inches of the stalk. I put a piece of tape around the
remaining stalk to mark the tubers. The plants sometimes are wilted, frozen
or still green. I have heard that the plants should be cut away after
the first frost, but the tuber should remain in the ground for five to
10 more days. Sometimes I cut into one of the tubers of the clump, so
I cut this tuber away from the clump and throw it away. Is this tuber
still OK? As I mentioned, I use tape around the stem to mark the colors.
However, often the tape comes off by the time I’m ready to plant.
Can I use a permanent marker on the tuber? (e-mail reference)
A: You can dig up
the tubers right after the first hard frost. The plant then is shut
down physiologically for the season. Shake off the soil, and yes, you
can use a permanent marker on the tubers. Any tuber will grow as long
as it is healthy and there is a bud or “eye” at the stem
end. If that end is broken off, it very likely will not produce a new
plant.
Q: I have read that
I should put mulch around dahlias. This is supposed to help keep the ground
moist and protect them from the hot sun. Can I use grass clippings? What
are other alternatives? (e-mail reference)
A: Any kind of well-weathered
organic mulch will benefit any plant, provided it isn’t overdone.
A 2- to 3-inch layer is ideal. If you use more than that, problems such
as slugs, soil kept too cool/moist and reduction of air to the roots
begin, causing the plants to migrate into the mulch, which defeats the
purpose. Grass clippings can be used as long as they have not had any
broadleaf herbicides applied during the last three mowings. Keep in
mind that grass clippings are “green manure” and too much
will cause heating and possible damage to the plant. If you have an
area to spread the clippings out for a day or two to dry before spreading
them around the plants, that would be ideal.
Q: I bought six emerald
green arborvitae-pyramidalis and planted them 3 feet apart to form a hedgerow.
They are planted at the top of a hill, getting partial sun. The problem
is that they are now slowly browning. I don’t know what to do to
save them. Could this be a normal occurrence in this type of evergreen?
(e-mail reference)
A: You are attempting
to close the barn door after the horses have departed. The plants are
being badly desiccated from the wind/sun/cold exposure. Back in October,
you should have sprayed the plants with an anti-desiccant such as Wilt-Pruf.
If you have any daytime temperatures between now and spring thaw that
reach into the mid-40s or higher for the day, you still can spray the
material on the foliage to prevent further damage. Don’t give
up. About eight or nine years ago, we had a Chinook wind blow through
the state while everything was under 2 feet of snow and the ground frozen
solid down to about 4 feet. Just about every evergreen in the state
that was exposed to the sun and wind fried brown. We thought they were
all dead, but around June or early July, many began greening up. Hang
in there until mid to late June anyway. These are pretty hardy plants,
so they just may survive.
Q: I’ve had
an aloe vera plant for more a year. It was given to me in a plastic bag
filled with water. I put the bag in a bowl when I got home. I never have
replanted it because I’m afraid that it will die. I keep water in
it all the time and it never has died. I would like to transplant it to
a nice pot and have it get larger, but I’m not sure how. (e-mail
reference)
A: I am surprised
that the aloe has survived this long in only a water culture! Aloe and
other succulents should be grown in containers and repotted when necessary,
but only into the next nominally larger container. Be careful to adjust
your cultural practices, especially watering, to reflect this move.
Repotting, in most instances, is done close to spring. Supplementing
with additional plant lights or providing adequate natural light usually
will result in full-sized leaves. Being a succulent, it should be watered
minimally in winter, kept in bright, indirect light, summered outdoors
and watered moderately the rest of the year. Allow the potting soil
to go dry between waterings.
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: Ron
Smith, (701) 231-8161, ronsmith@ndsuext.nodak.edu
Editor: Rich Mattern, (701) 231-6136, richard.mattern@ndsu.nodak.edu
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