AND SOIL LAYER BUILDING
OK! So you made it to Site Preparation.
Congratulate yourself! You are over halfway there (learning
your native and making a naturescape plan are usually
more time-consuming). And recognize that now is when
the real fun begins - you get to be outside and maybe even get dirty!
The site-preparation you will do (or have
done) will depend significantly on your site. It may
entail removing trees, killing grass, removing invasive plants (such as English ivy,
Himalayan blackberry, kudza, vinca, or other), and
amending/restoring damaged or compacted soil, etc. We
will focus first on transferring from a grass lawn to
a naturescape because that is the situation in which
most people find themselves. We will then discuss some
of the other situations.
From Turf Lawn
In transferring from a turf lawn to a naturescape it
is important to realize that you are not just removing
grass and planting natives, but you are restoring the
soil or soil "layers" at your site.
To help appreciate what this means, we
would like to distinguish between mineral soil and organic
soil. We will use the term mineral soil to generally
refer to soil that has a low organic component - we
often call this "dirt" and it tends to be rather hard when dry. We will use
the term organic soil to refer to soil that is comprised
largely of decomposing leaves, needles, and other organic
material - it tends to be soft and moisture-absorbent.
Organic soil layer - Fingers penetrate easily
Can you remember the last time you went
for a walk in the woods or other natural area? What
type of soil did you find (assuming you actually looked)?
You probably found an organic soil layer of 3-4 inches
(generally 1 to 6 depending on conditions) which gave
way to a mineral soil layer. You may have also noticed
that the herbaceous plants (the non-woody plants that
often grow close to the ground) tend to grow in the
organic soil layer, while the shrubs and trees tend
to grow in the mineral soil layer.
Contrast the local woods or an undisturbed
site with a turf lawn. Have you ever driven a shovel
into a turf lawn? What soil layers did you find there? We suspect that you found only the
mineral soil layer.
That is because prior to installing a turf lawn, the
organic soil layer is typically stripped off.
While some herbaceous plants can support
being planted directly in mineral soil, particularly
sun-liking perennials such as grass, etc., most herbaceous
plants, particularly the partial-shade and full-shade
liking ones (those found among trees and shrubs) need
an organic soil layer. Accordingly, if you will have
anything other than a full-sun meadow (or sand based
"desert-scape"), it is preferable to have an organic
soil layer. And, regardless of whether you are planting
a full-sun meadow or a partially- or fully-shaded space,
there is benefit in establishing at least some organic
soil layer because it provides weed-suppression and
soil moisture retention.
That is why, in essence, we suggest that
in changing from a turf lawn to a naturescape you're
not simply switching plants, but rather restoring the
soil layers. And don't worry now about how we do that
- it is fun, easy and inexpensive and we'll discuss
it more below. First, however, let's take out some lawn.
… Yeah, let's get out our tools, put on our boots, and
go "kick some grass!" [Yeah, we know, cheezy humor,
but we couldn't resist]
There are primarily two ways to get rid
of grass (1) dig it up, and (2) smother it. If you live
in an arid climate there is a third, stop watering and
wait. And if you are extremely patient there is a fourth,
plant trees and they will naturally kill the grass by
shading it out (may take 5-10 years). Here we will discuss
the first two, and how to re-establish the organic soil
Digging it up!
When it comes to digging up grass, you
will likely need a rototill and rake or for smaller
areas or folks who like to do things by hand, a shovel and/or pick and rake. For do-it-yourselfers,
local rental shops often carry rototills. The larger
self-propelled tillers (12-16 hp) tend to work well
for average lawns. Rototills work best when the lawn
and soil are somewhat dry. If too moist, you may create
a mud bath.
Regardless of whether you use a rototill
or do it by hand, thoroughly turn over the soil and
rake away the grass. The goal is to remove as much of
the grass plants as possible so that the grass does
not grow back into the space creating a maintenance
issue. After tilling and thoroughly raking you should
be left with smooth exposed dirt.
It is important to recognize that if you
add water (rain, fog, etc.) to the exposed dirt you
often get "insta-weeds" (not having "exposed dirt"
is one of the benefits of the smothering technique discussed
below). To help prevent or minimize this, we recommended
that you be ready to plant your plants
and otherwise cover the exposed dirt
as soon as possible after it is cleared.
As discussed in more detail below, we
recommend that you first plant your trees and shrubs
in the exposed soil. Next we recommend that your cover
the remaining exposed soil with a material that is both
(1) an organic soil layer builder and (2) a weed suppressor.
The number one material that we recommend for this is
leaf mulch. Our second choice is a thick layer
of leaves, though leaves tend to only be available in
the fall and are more likely to blow away. Grass clippings
and/or straw would be a distant third (distant
because it is unnatural to have such a high concentration
of cut grass, though the grass clippings could be mixed
in with leaf mulch or leaves). Note that if you live
in an area that has predominantly needle bearing trees,
you can substitute the words "needle mulch"
for "leaf mulch" in the present discussion.
Leaf Mulch - Organic Soil Layer
& Weed Blocker
Leaf mulch is decomposing leaves and is about the closest
commercially available substance to the organic soil
layer that you are attempting to replace. Thus, it is
the growing medium for a number of plants that you might
want to plant. It is also an excellent weed suppressor.
In addition, leaf mulch is relatively weed seed-free
(leaves are not the reproductive parts of plants) and
it breaks down relatively quickly, thereby releasing
its nutrients to your desired plants (i.e., a natural
Caution on Yard Compost and No
In contrast, try to avoid commercial yard debris composts
because they are often of unknown origin and contain
weed seeds. The provider may claim that the weed seed
are all dead, but in reality that is rarely the case.
Also, avoid bark mulch because it is
slow to break down, low in nutrient value, supports
weed growth, and quickly becomes a maintenance problem.
Bark mulch is only popular because
it is aggressively marketed, and returns profits to
its producers and the maintenance folks that are hired
to spray chemicals on it and/or manually pull weeds
from it. Large quantities of bark mulch covering ground
is also an unnatural condition and thus there are no
native plants that evolved to grow in it.
We will discuss below how you might obtain
leaf mulch and how you might use it. First, however,
let's discuss the other method of getting rid of grass
- smothering it - so that you can contrast the two methods
and decide what is right for you and your situation.
While there may be a time and a place for removing grass
by digging it up, that approach can be fairly labor-intensive
relative to smothering it. In addition, and, perhaps
of greater concern, digging up grass leaves bare soil
which is a magnet for weeds. Thus, the smothering or
obstruction method may have its advantages.
The smothering method is pretty straightforward
though when practiced most effectively it requires some
advanced planning and some patience. A typical approach
would be as follows:
Cut the turf grass to the lowest setting
on your mower and then cover it with newspaper at a
thickness of 10-16 sheets. Be sure to overlap the newspaper
sufficiently so that cracks don’t appear through
which grass and weeds can grow. This starts the smothering
process. Next, apply either several inches of leaf mulch
(4-6 inches) or a thicker layer (6-8 inches) of leaves
alone, or a combination of the two. If you use leaves,
it is a good idea to wet them down so that they will
stick together better. Note that while 6-8 inches of
leaves might seem like a lot, a good rain may reduce
that height in half.
Using newspaper and leaves to
The layer of leaf mulch or a greater thickness
of leaves alone works in combination with the newspaper
to block photosynthesis, which effectively kills the
grass. The leaf mulch and/or leaves also provide the
organic soil layer (the leaf mulch more rapidly than
the leaves). The newspaper (a wood product) will breakdown
and also contribute to the organic layer.
Smothering complete - "Good-bye
After application of newspaper and the
appropriate leaf material, we suggest that you wait
two months (and maybe more in the winter).
This is where the advances planning and patience comes
in. After two months, the grass should be sufficiently
dead that you can pierce the leaf layer and newspaper
at desired locations and plant your trees and shrubs.
Note that when planting through the leaf and newspaper
layer it is important that any dug up mineral soil not
remain on the surface (it must be removed or covered)
because it is a desired growing medium for many common
weeds (whereas a leaf mulch or leaf layer is not). The
herbaceous plants can be planted through or in the leaf
layer as appropriate.
In the photo above, the trees where
planted first and then surrounding ground was covered
with newspaper and leaves. Two months later, shrubs
where planted around the trees and herbaceous plants
planted in and through the remaining leaves and newspaper.
The same space now looks like ...
2.5 years later - Notice trees,
shrub layer and herbaceous layer
- Getting it and using it
OK! Now we've sold you a little on the idea of
leaf mulch. Now where, for Heavan's sake, do you
get it? If you don't have your own leaf pile left
over from last fall, this might require a little
searching. Fortunately, however, more and more
sources are popping up all over the place. The
first place to check is your local municipality.
If your city or other governmental entity collects
leaves in the fall, then they must do something
with those leaves. In contrast to "dumping 'em
somewhere -> the old approach, many municipalities
are turning their leaves into mulch which is used
on public property or sold to individuals or landscape
professionals for gardening and landscaping. The
City of Portland, Oregon, for example, windrows
their leaves, monitors the internal temperatures
of the rows to "cook" any weed seeds and facilitate
breakdown, and turns the rows when appropriate.
The available leaf mulch is typically from leaves
collected a year ago.
City collected leaves turning into mulch
One year later - Leaf Mulch ready to go!
The City of Portland, Oregon, charges
$16/cubic yard, and the lot is located at __________
(off NE 33rd by the airport). Call _________ for
hours of operation. If you cannot make it during
opearting hours or do not have hauling capacity,
you can call a private hauler often found in the
service directory listing in the local newspaper
- in this case the Oregonian. Note that if your
municipality does not have a leaf mulch program,
let them know that they should.
A second source
of leaf mulch is private processors. Landscape
products companies - the same folks from whom
you might have previously purchased bark mulch
- may sell leaf mulch. For example, in Eugene,
Oregon, Lane Forest Products (www.laneforestproducts.com)
sells leaf mulch. Note that smaller cities might
contract out leaf collection. If this is done,
find out who the leaf collection contractor is
and when they provide leaf mulch. Good luck, and
let us know if you find a good source in your
community. We'll post it.
Leaf Mulch - At the house
With respect to using leaf mulch,
we suggest that you spread the leaf mulch over
the area you intend to naturescape to a desired
depth. In areas that will have trees and shrubs,
ie, the ground will be partially or fully shaded,
we suggest approximately four inches. In areas
that will have full sun, we suggest approximately
two inches. Also, if you live in a more arid region
you might use less. This is good for starters.
Note that you can find out what works best in
your situation by trial and error and that leaf
mulch is an actively decomposing substance. The
four inches you apply in the fall may be three
inches in the spring.
We suggest that you apply the organic
soil layer and then plant your herbaceous plants.
Note that this suggested approach is just that
- a suggested approach. Deviate as appropriate
for your space.
Removing Hard to Remove Invasives
- Some of us are unlucky enough to have English
Ivy or Himalayan Blackberry or Kudza or Vinca
or some other invasive exotic plant that we are
challenged to get rid of. We cut it and it growns
back. We turn our back and it spreads to 10 new
locations. We might even despair and ask ourselves,
what's the point, we'll never get rid of it.
But the answer is acutally that
we will get rid of it. The important thing to
remember is that plants need to perform photosynthesis
to survive. If you interrupt photosynthesis, you
will kill the plant.
Applying this to the task at hand,
these and similar species can be removed by cutting
them low to the ground and then continually cutting
them and/or smothering them. If you can pull or
dig the plant out by the roots, good. If you can't,
cut them back to the ground. The plants will grow
back from energy stored in the roots and will
attempt to perform photosynthesis to recharge
the roots. If you cut the new shoots before they
have much time to perform photosynthesis, you
reduce the rate at which the roots are recharged.
The roots will again put out shoots, but if you
cut these shoots quickly, the roots begin to die.
You can repeat this process until the roots, and
hence the plants, are completely dead. The key
is to stay on top of it, and cut the regrowth
If the plant proves hard to kill,
you can also try smother it - and with something
more than newspaper and leaves. Cut it back to
the ground as described above, and then place
cardboard or wood or the like over it. If necessary,
use stones or stakes to secure your barrier. For
stubborn plants, you may have to combine smothering
and frequent cutting, i.e., smother the new shoots
and pick up the barrier from time-to-time to cut
the new shoots.
If the plant still proves to be
stubborn, you may consider a chemical pesticide.
If you do, we recommend that you use a more mildly
toxic one and that you apply it only when dry
and not windy, so that it does not run off. Note
that we do NOT advocate the regular use of pesticides,
but feel that limited use may be a "necessary
evil: to achieve a better, long-term end. PN
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