Here's a backward question. At my apartment complex, there are long
stretches of flower beds where the only thing growing is the usual generic
evergreens. I have not seen a single plant growing there since the ground
thawed in April. I know for a fact that nobody's doing any weeding, but I
*do* know that last September, some ancient man was walking around with a
tank & sprayer, hosing down all the bare spots. Even so, I'd expect
SOMETHING to pop up almost a year later. He had no idea what he was
applying - "They just told me to spray what was in the tank".

This is just curiosity on my part, but what could he have applied that would
kill everything for such a long time? By the way, there's no weed barrier in
these beds - it's about 25% covered with some faded wood chips, but that's
all.

"Doug Kanter" wrote:

At my apartment complex, there are long
stretches of flower beds where the only thing growing is the usual generic
evergreens.

Many of these "generic" evergreens shed needles (or scales) that are
preemergence herbicides and prevent weeds from coming up from seed. One
good examples is juniper Virginianis. That is why some forests have few
weeds on the forest floor.

--
Pardon my spam deterrent; send email to
http://home.earthlink.net/~rhodyman

"Stephen M. Henning" wrote in message
news
"Doug Kanter" wrote:

At my apartment complex, there are long
stretches of flower beds where the only thing growing is the usual
generic
evergreens.

Many of these "generic" evergreens shed needles (or scales) that are
preemergence herbicides and prevent weeds from coming up from seed. One
good examples is juniper Virginianis. That is why some forests have few
weeds on the forest floor.

Really? Even 5-6 feet away from the shrubs themselves?

"Stephen M. Henning" wrote in message
news
"Doug Kanter" wrote:

At my apartment complex, there are long
stretches of flower beds where the only thing growing is the usual
generic
evergreens.

Many of these "generic" evergreens shed needles (or scales) that are
preemergence herbicides and prevent weeds from coming up from seed. One
good examples is juniper Virginianis. That is why some forests have few
weeds on the forest floor.


This is not exactly true - allelopathy is not exactly the same as a
pre-emergent herbicide, although the effects can be somewhat similar. And
the lack of weeds or significant undergrowth in heavily forested areas is
most often due to competition of the larger root mass of the trees for
nutrients and soil moisture combined with persistant shade from the forest
canopy. In more open areas, weed and native growth is generally pretty
prevalent.

The lack of weeds in this case is probably a combination of factors. There
are some pretty heavy duty herbicides out there which are commonly used in
the maintenance of commercial properties plus many wood-based mulches have
allelopathic properties of their own, albeit small and not very longlasting.
Also, many pre-emergent herbicides can have a rather longlasting effect -
upto about 9 months. That combined with the fact that most common weeds seed
in fall or spring (but not in summer) can account for the fact that you
haven't seen any significant weed development yet.. If no further spraying
is done this fall, I''ll bet you see some weeds start to develop with the
fall weed crop and the autumn rains.

pam - gardengal

"Pam - gardengal" wrote in message
news:kK7Tc.301797$XM6.35745@attbi_s53...

"Stephen M. Henning" wrote in message
news
"Doug Kanter" wrote:

At my apartment complex, there are long
stretches of flower beds where the only thing growing is the usual
generic
evergreens.

Many of these "generic" evergreens shed needles (or scales) that are
preemergence herbicides and prevent weeds from coming up from seed. One
good examples is juniper Virginianis. That is why some forests have few
weeds on the forest floor.


This is not exactly true - allelopathy is not exactly the same as a
pre-emergent herbicide, although the effects can be somewhat similar. And
the lack of weeds or significant undergrowth in heavily forested areas is
most often due to competition of the larger root mass of the trees for
nutrients and soil moisture combined with persistant shade from the forest
canopy. In more open areas, weed and native growth is generally pretty
prevalent.

The lack of weeds in this case is probably a combination of factors.
There
are some pretty heavy duty herbicides out there which are commonly used in
the maintenance of commercial properties plus many wood-based mulches have
allelopathic properties of their own, albeit small and not very
longlasting.
Also, many pre-emergent herbicides can have a rather longlasting effect -
upto about 9 months. That combined with the fact that most common weeds
seed
in fall or spring (but not in summer) can account for the fact that you
haven't seen any significant weed development yet.. If no further spraying
is done this fall, I''ll bet you see some weeds start to develop with the
fall weed crop and the autumn rains.

pam - gardengal



Hmmm. I'm glad I didn't plant any herbs or vegetables there.

I wrote:
Many "generic" evergreens shed needles (or scales) that are
preemergence herbicides and prevent weeds from coming up from seed. One
good examples is juniper Virginianis. That is why some forests have few
weeds on the forest floor.

"Pam - gardengal" replied:

This is not exactly true - allelopathy is not exactly the same as a
pre-emergent herbicide, although the effects can be somewhat similar.

Allelopathy is a variety of chemical processes that plants use to keep
other plants from growing too close. These compounds include alkaloids,
cyanohydrins, sulphides, flavaniods, terpenoids, steroids, phenolic
acids, aliphatic acids, glycosides, lactones, tannins, organic acids,
purines, nucleotides, cinnamic acid and sugars. In one kind, the plant
that is protecting its space releases growth-compounds from its roots
into the ground. New plants trying to grow near the allelopathic plant
absorb those chemicals from the soil and are unable to live. A second
type of allelopathy releases chemicals that slows or stops the process
of photosynthesis . An allelopathic plant may also release chemicals
that change the amount of chlorophyll a plant has in it. When a plant's
chlorophyll levels are changed, it cannot make the food it needs, and
the plant dies.

Some plants that use allelopathy are black walnut trees, sunflowers,
wormwoods, sagebrushes, and trees of heaven.

There are several ways in which an allelopathic plant can release its
protective chemicals:

Volatilization: Allelopathic trees release a chemical in the form of a
gas through small openings in their leaves. Other plants absorb the
toxic chemical and die.

Leaching: All plants lose leaves. Some plants store protective chemicals
in the leaves they drop. When the leaves fall to the ground, they
decompose. As this happens, the leaves give off chemicals that protect
the plant.

Exudation: Some plants release defensive chemicals into the soil
through their roots. Those chemicals are absorbed by the roots of other
trees near the allelopathic one. As a result, the non-allelopathic
tree is damaged.

Some pine trees are allelopathic. When their needles fall onto the
ground, they begin to decompose . The soil absorbs acid from the
decomposing needles. This acid in the soil keeps unwanted plants from
growing near the pine tree. It has been theorized that phenolic acids
present in pine leaves may play a vital role in the allelopathic
inhibition of understory species. Hence, many pine forests have very
little on the forest floor other than pine needles.

Many junipers produce a phenolic compound found to inhibit seed
germination. Such a compound is called a preemergent herbicide.

--
Pardon my spam deterrent; send email to
http://home.earthlink.net/~rhodyman

"Doug Kanter" wrote:

"Stephen M. Henning" wrote:
Many of these "generic" evergreens shed needles (or scales) that are
preemergence herbicides and prevent weeds from coming up from seed. One
good examples is juniper Virginianis. That is why some forests have few
weeds on the forest floor.

Really? Even 5-6 feet away from the shrubs themselves?

It depends on the spread of needles or scales. The chemicals are
released from the needles or scales. If they get scattered around, then
the toxic effect is scattered around.

--
Pardon my spam deterrent; send email to
http://home.earthlink.net/~rhodyman

In article , "Stephen
M. Henning" wrote:

"Doug Kanter" wrote:

"Stephen M. Henning" wrote:
Many of these "generic" evergreens shed needles (or scales) that are
preemergence herbicides and prevent weeds from coming up from seed. One
good examples is juniper Virginianis. That is why some forests have few
weeds on the forest floor.

Really? Even 5-6 feet away from the shrubs themselves?

It depends on the spread of needles or scales. The chemicals are
released from the needles or scales. If they get scattered around, then
the toxic effect is scattered around.

But additionally plants like junipers sometimes grow in hard compacted
organically depleted & dry soils that little else can get a foothold in.
If the whole area had its soil loosened & some peat worked into it, & a
bit of water gotten to the improved soil, there are a whole host of plants
that actually thrive in the environment created by junipers or walnuts &
other trees & shrubs that exude growth-retardants -- such as virginia
creeper, daffodils, grape hyacinths, daylilies, cranesbills, sweet
woodruff, & a god's plenty of weeds.

-paghat the ratgirl

--
"Of what are you afraid, my child?" inquired the kindly teacher.
"Oh, sir! The flowers, they are wild," replied the timid creature.
-from Peter Newell's "Wild Flowers"
Visit the Garden of Paghat the Ratgirl: http://www.paghat.com

"paghat" wrote in message
news
In article , "Stephen
M. Henning" wrote:

"Doug Kanter" wrote:

"Stephen M. Henning" wrote:
Many of these "generic" evergreens shed needles (or scales) that are
preemergence herbicides and prevent weeds from coming up from seed.
One
good examples is juniper Virginianis. That is why some forests have
few
weeds on the forest floor.

Really? Even 5-6 feet away from the shrubs themselves?

It depends on the spread of needles or scales. The chemicals are
released from the needles or scales. If they get scattered around, then
the toxic effect is scattered around.

But additionally plants like junipers sometimes grow in hard compacted
organically depleted & dry soils that little else can get a foothold in.
If the whole area had its soil loosened & some peat worked into it, & a
bit of water gotten to the improved soil, there are a whole host of plants
that actually thrive in the environment created by junipers or walnuts &
other trees & shrubs that exude growth-retardants -- such as virginia
creeper, daffodils, grape hyacinths, daylilies, cranesbills, sweet
woodruff, & a god's plenty of weeds.


I agree with this. Once you kill off all the perennial weeds and let the
soil surface crust over, weeds just don't grow. If you break-up the surface
and mix in some organics to prevent it from crusting over, all kinds of
weeds will grow.