Thursday, March 7, 2019

Eastern Bottlebrush Grass

Bottlebrush grass, Elymus hystrix, is a pretty common native species found in open shade and woodland edges in Maryland.  Its native range is from Maine to Georgia and westward to the Great Plains.   It is a cool season grass, meaning that it begins grows actively when soil temperatures are between 50 and 65 F.  Attractive seed heads are produced in June and these often persist into the fall.  Like most cool season grasses it shuts down in the heat of summer, but comes back to life in the fall, sometimes staying green all winter.  I am looking at using this grass to help fill in the woodland edges after removing the invasive Japanese stilt grass, Microstegium vimineum.  Ideally once it gets established it will grow up and shade the ground before the stiltgrass germinates later in the spring.

Eastern Bottlebrush Grass at the end of June growing along a trail near Harper's Ferry, WV

Rather than buying new seed, I harvested some from my existing plants last October and stored them dry in a refrigerator at about 42-45 F.  They were left there until I planted them in mid-February under lights.  Bottlebrush grass seeds do not require moist stratification to get them to germinate, just cold storage for a few months.


Since I have had less than stellar success with starting seeds I thought I would compare different ways of planting the seeds and see how well each germinated.  This was a limited study with only 8 seeds under each of 8 conditions.  All were planted in a soil-less seed starting mix and put on a warming pad to give a soil temperature between 65 and 70 F.  The long awns on the seeds, which give the brush effect, are not easily removed.  I pulled the awns off of each individual seed.  For these I planted one set vertically, and the next horizontally, each about a quarter inch deep.  The third set I planted vertically about a half inch down.  I repeated these conditions using seeds with the awn still attached.   


Here's the first leaf of Eastern Bottlebrush Grass.  The inital shoot has a reddish
 tinge that makes it harder to spot on the dark background. 
The last set of seeds were moved to a colder refrigerator for about a month.  I thought this might simulate winter conditions better.  One set of these I cleaned and planted horizontally, and the other was with the awn attached and planted vertically. 

Seeds began germinating after 9 days.  Rather than going into too many details the results indicated that seeds that were cleaned germinated more quickly, but after a month there was little difference between cleaned and uncleaned seeds.  Where I did see a difference was with colder storage.  Seeds stored in the back of the refrigerator germinated at half the rate of the others stored at about 44 F.  I suspect at the back of the frig, where the coldest air comes in, temperatures would sometimes drop below 32 F.


Now I have about 30 plugs of a native grass that I can grow on to use in my battle against stiltgrass.

Saturday, February 2, 2019

Garden Trellis

My vegetable gardening style is on the wild side.  I give maybe too much weight to reseeded native flowers over food producing plants.  I start out with grand expectations of neat rows, but inevitably weeding the garden becomes less important as other tasks loom.  In fact this year I got things nicely cleaned up with weeded and fertilized beds and mulched paths.  Unfortunately reality struck with a cool wet spring that offered few pleasant days to keep the garden neat and clean.

I got the garden all cleaned up in April of 2018 with great intensions
 for keeping it neat, but ...
One way to bring order to the garden is to add visual structural elements.  These add focal points or visual anchors that rise above the clutter.  In past years I've used fallen limbs to create tripods to support beans, cucumbers and tomatoes.  Since these were not well anchored, they end up falling over as the season wears on.  This year I decided to build some semi-permanent tripods that could be left standing for a couple of seasons and could be easily repaired if and when the time comes.

Schematic for my garden trellis.  Parts include 2x2 wooden legs, 3" diameter PVC pipe,
 6" wood square, some 2.5" deck screws and a bag of coarse sand.

I liked the idea of using tripods.  They are easy to build and structurally sound.  Here is a schematic plan that I came up with for my tripod trellises.  I wanted to build it out of 2 by 2 cedar, but it was not readily available in long lengths.  Being somewhat impatient I got 2 by 8 pressure treated boards that I ripped into 3 1.75" wide pieces about 7.5' long.  Before ripping into thirds, I cut off a 6" piece (actually 6" x 7.5") to make the top support.  I trimmed this rectangular piece into a hexagon on the band saw and angled 3 of the faces at 12° to match the angle of the tripod (see the diagram).



Completed intallation of tripod legs.  Having the PVC sleeve
 above the soil level helps keep the sand clean.
 Rather than driving the trellis directly into the ground, where constant contact with wet soil would accelerate rotting of the wood, I put in a length of 3" PVC drain pipe that I would later fill with sand to make well draining fill that would also hold the trellis firmly in place.  (Note that the thinner schedule 40 PVC drain pipe can be used rather than schedule 80, since you are just forming a soil barrier.)  To further improve the weatherability I also painted the lower 2 feet of the wood with a water seal coating. 

My biggest mistake last year was getting started too late in the season, after the garden had started growing. To put in the PVC liners in the established garden I used a trenching shovel (about 3" wide) to dig a fairly narrow hole in at a roughly 12° angle and 16-18" deep.  I then used the PVC tube itself to remove the last bits of the soil and get a firm fit.  The other two liners were put in 31" away from the first to form an equilateral triangle (see the diagram). 

The top support is attached to the legs
with 2.5" deck screws.  These are easily removed
 if I needed to replace one of the legs.
After the liners were in, it was time to position the legs of the tripod.  With the 3" lined holes there was sufficient wiggle room to get the legs to align.  The top hexagonal support was attached to the legs with 2.5" deck screws. The screws were prepositioned about 9" from the ends of the legs so that I only had to drill them into hexagonal support (into the angled faces).

The completed trellis, with a spiral of twine,
is ready to support these cucumbers.
With the top support attached and the legs in their PVC sleeves I filled in the space between the sleeves and legs with coarse sand.  First I put in about an inch of sand as a base under the legs then finished by back filling with sand to the top of the sleeve with occasional tapping to make sure the sand was evenly and firmly distributed. It took a little over a half cubic foot of sand to to do 4 tripods (12 holes).

Even with this late start I was able to train the tomatoes and cucumbers onto the trellises that I had built around them.

I tied some rubber balls to the blunt top ot the tripod using fishing line. 
The lightweight balls won't damage the plants if they fall off.

Now I am again getting ready for a clean start in the garden.
It's February and the trellis are ready to go.  Well, maybe in a couple of months.

 

Tuesday, January 8, 2019

What to do with old potting soil?



Here's about half of my potted plants that I do each spring.

I hate to throw out used potting soil.  I have about 30-40 pots in various sizes.  If I were to change out the soil every year I'm looking at buying 150-200 quarts of new soil each time.  Then I would also need to get rid of the used stuff.  In many cases potting soil can be reused for two or three seasons with a little refresher.   Here are three things you can do with used potting soil.

Here's whats left as the growing season ends.  These will all be brought in
under cover to avoid damaging the pots in freezing weather.

Rejuvenate it:  I've reused potting soil for several years.  It does degrade over time and will benefit from being rejuvenated.  The biggest problem is when it gets too dense and no longer drains well.  Can also make it more difficult for roots to grow and it gets soggy.  Old potting soil has also lost whatever fertilizers were there at the beginning, so nutrients will need to be added.  Espoma Flower- or Plant-tone are good organic choices.  Osmacote slow release fertilizer is another good choice, though not organic.  Compost is also a good form of fertilizer, but too much, any more than one third by volume, in the potting mix can decrease drainage and soil aeration.  Last year I tried using alfalfa pellets stirred into the container mix where I was growing tomatoes in pots.  It gave moderate results, but I think I needed to use a lot more or more frequent additions to get sustained results.  (The NPK value for alfalfa pellets is about 3-1-2.)  

To lighten up older potting soil you can mix in fresh peat moss or coir and/or pearlite.  To improve drainage some sand could also be added, but that ingredient does not get depleted from one year to the next.  I am torn about leaving old root balls in the container mix.  They slowly decompose to build organic matter, but they also are places where the soil is denser and they may harbor some plant pathogens.  I am tending to pull most of them out now and throw them into the compost pile.  Also pick out any bugs and weeds that you see.  I've seen warnings about not growing tomatoes in the same soil two years in a row.  This is due to root pathogens carring over from one year to the next.  That being said, I have replanted tomatoes in the same soil and they have survived, but I would recommend following the recommendation if your tomatoes have suffered any fungal disease.  If you believe your soil is infected with pathogens, or if it is loaded with weed seeds it can be pasteurized by warming it to 120 F for 30 min.  This can be done by putting to soil in black plastic bags and placing them in full sun.  Note that the more soil there is in the bag the longer it will take to get up to the right temperature.  

For more tips on reusing potting soil see:  https://www.springpot.com/blog/reusing-potting-soil/

Use it in the garden to lighten heavy soil.  Mixing old potting soil into heavy garden soil is a pretty effective means of adding long lasting organic matter to the soil.  I've done this and even after two seasons the soil is noticeably lighter and easier to work with.  The down side is that any viable seeds from your potted plants are now in your vegetable garden.  As a result I now have scarlet sage and torenia scattered through the vegetable garden.  Had I pasturized the soil this problem could have been avoided.

While my vegetables are planted in neat rows, volunteer seedlings are filling in all the gaps. 
This photo was taken in mid-July so the salvia has not yet reached full size - it gets 'worse.'


Throw it in the composter.  This should be a no brainer, but I had not considered it until I read about doing this recently.  Potting soil adds 'brown' material to the composter.  Since we use our composter mostly for kitchen waste (mostly 'green' or high nitrogen materials), it is in need of 'brown' or high carbon materials to balance it out.  After adding a load of old potting soil I noticed an almost immediate increase in composter temperature.  This practice also carries a risk of spreading seed from the potted plants, but if the compost gets up to temperature (120-140F) for several days most of those seeds will be killed (as will most plant pathogens).

Do you have any other tips for using old potting soil?  I would love to hear them.


Tuesday, December 11, 2018

Inkberry berries



This past spring I replaced some non-native Leatherleaf Mahonia, Mahonia bealei, with inkberries, Ilex glabra.  While moderately invasive, the mahonia did produce a decent crop of berries over the winter which was available to the resident bird population.  I wanted to make sure that these inkberries would also produce berries that the bird could use through the winter. Inkberries, like most other hollies, tend to be dioecious, that is have male and female flowers on separate plants.  Most inkberries commercially available are listed as being female.  The only male cultivar I could find listed is 'Nordic', which was selected for is cold hardiness.  Here in the relatively warm Mid-Atlantic, I couldn't find any for sale.  I did find a mention that you could use another species of male holly as long as it blooms at the same time as the inkberry.  Jim Dandy winterberry holly, Ilex verticillata 'Jim Dandy' (blooming in late May-early June), seemed to be a good fit for inkberries which bloom from about mid-May to mid-June.

The selection of native hollies that I put in to replace the leatherleaf mahonia.  Left to right:
Jim Dnady winterberry (male), Nigra inkberry and Shamrock inkberry (both female)

The selection of inkberries I settled on were two Shamrocks and one each of Densa and Nigra.  The Shamrock cultivars a supposed to top out at around 4' while the other two should grow larger to about 6'.  By having a mix of cultivars I hope to add a little extra texture and variation in height to this planting.  Right next to these I put in the Jim Dandy winterberry, to help with fertilization.

Here's the Shamrock inkberry at the end of May.  Looking closely
you can see some of the flowers have anthers with pale yellow pollen. 
Other flowers are lacking stamen, but have a large central ovary.

This Nigra inkberry has only female flowers.  The flowers are
not in dense clusters like many of the male flowers on the Shamrock cultivar.

At the end of May the flowers on this male winterberry are just opening up. 
This timing overlaps with the flowers on the inkberries.

As the inkberries were blooming I paid attention to when the flowers were opening up on each plant.  To my surprise I noted that the Shamrock inkberry seemed to have both male and female flowers on it.  The Nigra and Densa cultivars appeared to have only female flowers.  I would have thought that if the Shamrock cultivar is typically monoecious (have both flower genders on one plant) then that should be called out in the description of the plant as this would be a great benefit to wildlife gardeners. 

Fast forward to mid-fall and there are reasonable numbers of black berries on both the Shamrock and Nigra cultivars.  I can not say unequivocally that the Shamrock did all the pollination work since the male winterberry was right there in the mix, but at least I have been successful in replacing the leatherleaf Mahonia with a native evergreen shrub that provide berries for the resident bird population in the winter.

Got a few berries on this Shamrock inkberry.  It's missing
 quite a few leaves, my guess would be deer browse.
 Unfortunately the Densa cultivar died back by the end of summer.  Two possibilities are that it was in the shadiest spot of all the newly planted hollies, and/or that it is planted at the edge of the drip line of an English walnut, Juglans regia.  While not as potent as the native black walnut, Juglans nigra, the English walnut does produce juglone, a compound the inhibits the growth of a number of plants, including inkberries.  We'll see how the other inkberries overwinter before I find something to replace the Densa cultivar.



This Nigra inkberry also has a few berries, as expected.  It too
has taken some deer damage.  I've since sprayed them with some deer repellent.  


Wednesday, November 28, 2018

Monarch Successes in 2018

I've been planting native milkweed plants for 5 years here and that while I've seen a few monarch butterflies over the this time, 2018 is the first year that I've actually seen any caterpillars.  While this may have been destined, one thing that was different this year is that I included a couple of pots of tropical milkweed, Asclepias curassavica, into our mix of potted plants.  Since these new plants were on the deck where we could see them easily, it may just have been that the caterpillars were just easier to spot this year.  Or tropical milkweed is a preferred host, so that encouraged the females to lay eggs closer to where we could see them.  These caterpillars showed up around the beginning of August.  This corresponds to the third generation in the monarch migration.  

Monarch butterfly on a tropical milkweed, Asclepias curassavica.
Tropical milkweed is native to South America and has naturalized into tropical areas worldwide, including southern California, southern Texas and Florida.  It is winter hardy in USDA zone 9-11 and can be grown as an annual in colder parts of the U.S.  It has striking red and orange flowers that make it an attractive garden plant and its tender foliage seem to make it a preferred host for monarch caterpillars.  That being said there are a number of reasons to plant more of the native milkweed species rather than planting a lot of this 
tropical species.


Some people have cited concern that this tropical species may interfere with migration patterns, especially in the southern parts of the US.  There, the presence of large tropical milkweed population may fool the butterflies into stopping their migration before reaching their destinations in Mexico.  This has not yet been established by scientific studies.  One negative factor that has been proven is that tropical milkweed can host a parasite that can harm monarch butterfly populations in overwintering butterflies.  I would refer you to this link on parasites on tropical milkweed for a more detailed discussion of this issue.

The authors do not insist that all tropical milkweed be removed, but recommend that all green foliage be removed from over-wintering plants between October and February to prevent any parasites from surviving and infecting any of the northward migrating butterflies along the way the following season.  What would be best is to grow only native species which die back to the ground naturally each year, thus ensuring that there will be no parasites.

The remains of the tropical milkweed after 6
 caterpillars fed on it.

While we were thrilled with seeing the monarch caterpillars, we soon saw that there was a potential crisis developing.  Within a couple of days the caterpillars had totally stripped the potted milkweed plants of all of their foliage.  The caterpillers were approaching maturity (4th or 5th instar) but we still didn't want to risk starvation so close to maturity. 


Fortunately there were the native milkweeds elsewhere on the property.  Since the tropical milkweed was growing in pots, I was able to more the pots to where the native milkweeds were growing and encourage the caterpillars to migrate onto the other plants.  Before moving the caterpillars I tried to do some research into what are the preferred host plants in the Mid-Atlantic region.  Much of the info on the internet is anecdotal but I did find one scientific study that looked at nine North American milkweed species and reported the survival rates for caterpillars reared on each.  Of these nine I knew where I had three of them growing on my property: Common milkweek (A. syriaca), butterfly weed (A. tuberosa), and honeyvine (Cynanchum laeve).  

By August the caterpillars did not seem so interested
 in eating butterfly weed. 
While butterfly weed was among the better hosts based on that study, late in the growing season its leaves are relatively tough compared to my other two species (and much tougher than the tropical milkweed).  By placing the tropical milkweed pots among both common milkweed and honeyvine I was able to coax the caterpillars onto those plants.  

I was able to get the caterpillars to move onto the common milkweed plants.

The honeyvine, with its thin, tender leaves seemed to be a big hit.  This was a bonus for me since the honeyvine, which appeared last year as a weed, is an aggressive grower.  The caterpillars, which are aggressive eaters were a good match for the honeyvine and after a couple of days the vine had been eaten back to an acceptable level. 

Honeyvine is an aggressive vine, similar in habit to bindweed,
except with opposite leaves.  It's native to the
Mid-Atlantic and Mid-Western states.  The small white flowers
have an intense honey-like scent in late summer.

  

So, based on this year's experience I will try to keep the potted tropical milkweed in the sunroom over the winter so that I will have a head start on growth next spring.  To control potential parasites I will cut the plants down to within 6" of the soil and  remove all leafy sprouts between in late winter. 

Monday, September 24, 2018

Japanese Stiltgrass Sitrep


For the past 5 years, since moving to rural central Maryland, I have been trying to figure out how to eliminate Japanese stiltgrass, Mircostegium vimineum, from my property.  This has been the subject of multiple blogs over the years and, unfortunately, will be so for a few more years.  Here's a link to my previous post on stiltgrass.

This area in the woodlands took about 30 min to clear by hand
and filled about half of the basket.  Rosy sedge is growing well underneath.
In shady woodland areas pulling stiltgrass out by hand, or string trimming and removal of the cut grass, seems to be pretty effective.  Removing the grass in late summer, prevents a new crop of seed from being produced.  The shady conditions seems to limit germination and flowering of the stiltgrass so that the sheer  volume is more manageable.  Annual pulling has reduced the amount of stiltgrass significantly.  As the stiltgrass has been going down I am seeing more native species, like Virginia jumpseed, Polygonum virginianum.

In part to full sun areas pulling the grass alone has not been as successful.  In some beds, with lots of competition the amount of stiltgrass has been reduced significantly.  In more meadow-like settings I have not seen great results, despite removing large quantities of stiltgrass each year in mid-summer.  One possibility here is that there is enough seed produced in the cleistogamous flowers trapped at ground level by the undergrowth to regenerate the seed bank. 

Getting stiltgrass out of the lawn is a more recent area of focus. There are two methods that have been effective for me.  One is to use a garden torch to burn the stiltgrass to the ground in late summer-early fall.  This eliminates the cleistogamous seeds in the lower stems and, in late summer, it is too late in the year for new plants to mature.  The burned areas are immediately ready for reseeding and most perennial grasses present will regrow from the roots, as long as you don't overdo it with the torch.

Another method that I tried last year that has proven very effective in the lawn is to use a pre-emergent herbicide in early spring.  Most products that work on crabgrass should work on stiltgrass.  See this earlier post for more details.  I used a product containing 'Dimension' (Dithiopyr) and had areas that were free of stiltgrass through the entire season.  To battle stiltgrass, these herbicides should be applied a couple of weeks earlier than you would for crabgrass.  When the forsythia are in early to mid-bloom should be about right. 

In the treated area I applied 'Dimension' pre-emergent herbicide the 3rd week of March. 
Now, at the end of summer, it is relatively free of Japanese stiltgrass.  In the untreated areas you can see
the brownish color of stiltgrass as it is beginning to die at the end of the season.

One problem with pre-emergents is that they are pretty much non-selective and will inhibit the growth and/or development of most seeds in the soil.  (Dithiopyr also inhibits the growth of new roots, not so good for really young plants.)  They are not appropriate to use at the time of reseeding or on lawns that are not well established.  For this reason I am reseeding/over seeding as early as possible this fall so that the new turf can get established before I treat again next spring.  In 2018, I applied Dimension at the end of March, this year I will wait until early-April (mid-to-late in the Forsythia bloom) to give the new lawn some extra time to grow.

This is an area where I raked out the stiltgrass and thatch to prepare for overseeding.
Most of this debris came from the 'untreated' area.
This year I am overseeding most areas with a sun-shade blend containing tall fescue, red fescue and perennial blue grass.  I have also put down the 'No Mow' blend of red and creeping fescues in areas of open shade where there is less competition from other turf grasses.  I'm located on the southern edge of the 'cool season' grass zone.  If I were a few hundred miles further south where warm season grasses dominate, I would be trying the native buffalo grass/blue gamma grass mixtures.  Raking out stiltgrass from the lawn alone has not proven effective.  While it removes a large mass of stiltgrass, it likely leaves enough seed behind to continue the infestation.  Raking is still necessary if you are going to reseed, in order to provide access to the soil for the newly applied grass seed.


You can see how poor this unmown area looks after the stiltgrass has been pulled out. 
This area has since been overseeded with 'No Mow' fescue.  If the fescue germinates
well this fall, I will probably treat  this area with a pre-emergent come springtime.
One suggestion that I read about was to leave stiltgrass alone until late summer, then mow it down short.  The idea is that by not mowing throughout the summer, fewer cleistogamous seeds are produced and the late timing of this mowing does not give the plants an opportunity to produce new flowers.  I have had a hard time getting this to work for me.  If you leave the stiltgrass to grow for too long, all of the shorter vegetation is starved of sunlight.  I tried this technique in one area, and we will see how quickly the perennial grasses bounce back.




Wednesday, September 19, 2018

New Sloping Path

One area in my lawn has a steep grade, about 28%.  That is a rise of 4.5' over a 16' run.  The lawn tractor could make the climb, but usually left some tracks, particularly if the ground was moist.  Also when walking through that area it was a real chore.  This is a prime area to replace the turf with a lower maintenance planting and to put in some steps to make navigation easier.

When doing a project that involves both planting and hardscape (elements like steps, walls and patios) it is best to put in the hardscape first.  The positioning of plants has greater flexibility and there is usually less heavy lifting than when positions stones.

Overall Plan for this sloping site.  The 9 steps are shown as rectangles,
though in reality they are irregularly shaped.  The highest elevation is at the top,
sloping down about 4.5 feet to the lowest step.  Scale 1" = 3'.
The first step in putting in steps on a hill is to determine the slope of the hill and then position the steps.  Having a consistent rise and step length makes the steps easier to navigate.  The overall rise here was 54".  For a 6" rise/step, that calls for 9 total steps.  At this time you can also move the shrubs around, while they are still in pots, to determine how you would like to position them.

Here, after the steps were installed, you can see the level lines that were used to determine the overall slope
and to guide the installation so that the change in elevation from step to step was about the same.
(In the background you can see the tamper that is used to compact the soil and paver base.)

I try to use a sustainable approach to landscaping whenever possible.  In this case that means using stepping stone materials that were on site, left over from an earlier dry laid stone wall project.  These stones give a naturalistic appearance.  Also by using the same materials the two projects become visually and materially united.  One down side of using irregular stones as steps is that each step needs to be engineered individually to set it on a solid foundation.  Rectangular steps installed in a straight line require less customization.

For steps that get a lot of use a crushed stone base of 6 or more inches is recommended.  Since these steps are only for occasional use, I cut back a bit on the amount of base.  The riser for each step is supported by 2-3 inches of compacted paver base separated from the soil by a layer of landscape fabric over the compacted native soil.  Behind this reinforced riser is compacted fill.  Supporting the riser with a firm base gives the step a firm feel underfoot.  It's much more comfortable to step onto a firm, well seated step than one that wobbles even a little.

Here's a view underneath one of the steps showing the compacted paver base
underneath the the riser and the landscape fabric that is being used to hold the dirt
behind the dry-laid riser.  For some of the steps that were difficult to stabilize I used
construction adhesive to secure the step to the riser.

The standard formula for garden steps is that the tread length be about 26" minus 2 times the step height. 

Tread Length" ≈ 26" - (2 x step height")
So for a 6" step height the tread length should be approximately 14".  The formula is based on a comfortable stride length for the average person.  Had I put he steps in a straight row down the slope it would have been close to this formula.  Instead I spread the steps over a longer, curving course.  I thought that the slightly longer course would have made for an easier, more gentle climb, but instead the longer distance between steps makes the trip feel less certain, especially when going downhill.

However, the way I chose to do it created a more naturalistic look and used materials that were already on hand.  Also by following the existing slope I minimized the changes to the existing grading.  Looking back, if these steps were to be used on a regular basis or in a more formal setting I would have built a deeper foundation, used more regularly shaped stones and followed the formula more closely.

This is the area after scalping the grass with a string trimmer. 
I also used a garden torch (circled) along the edges to burn the areas that had
Japanese stiltgrass in an attempt to kill any new seeds/seedlings. 
Once the steps were in it was time to eliminate the existing grass and weeds.  (This could have been done before installing the steps, but I felt it was less disruptive to the stability of the slope to wait until the steps were in place.)  There were several options for getting rid of the existing turf and weeds:  dig it out, spray it with a broad spectrum herbicide, or cover/smother with cardboard and mulch.  Digging is a lot of work and could destabilize the slope.  Herbicide would be easy and would be less disruptive to the soil surface, leaving roots intact to hold the soil.  I opted for the cardboard smothering/mulching method.  It leaves the soil intact, is non-toxic, and there are limited debris to deal with.

I used thick cardboard from moving boxes to cover the unwanted grass.
After mowing/scalping the existing grass, I covered the slope with cardboard and pinned it in place with landscape staples.  After moistening the cardboard to make is more flexible to conform to the soil surface I covered it with 2" of wood chips.  Most of the lawn will die due to lack of light in a few weeks, but planting can be done sooner by cutting holes through the cardboard, removing all the exiting grass from around the area and inserting the new plant.  The re-exposed soil should be well mulched or recovered with scraps of cardboard to keep the old grass from growing through.

The cardboard was covered with about 2" of woodchips that were left by our
arborist this spring. I started planting about 10 days after spreading the chips. 
For the areas between the steps I dug out the grass by hand since it was hard to get small pieces of cardboard to stay in place and there will be a lot of gaps where the grass can peek out and get re-established.

Now it's time to plant...

The plants I chose for this area are all low maintenance natives that are from the mid-Atlantic area, mostly ones that grow nearby.  I chose plants that area fairly low-growing to minimize the amount of pruning needed to keep the pathway open, both physically and visually.  The selection of plants will have something in bloom from early spring through fall.  You can see the plant list in the drawing at the beginning of this post.

The Grow-Low sumac are at the foreground in this photo, with the Red Sprite holly at the back.
First to go in are the woody shrubs. I put in three Grow-Low aromatic sumac, Rhus aromatica 'Grow-Low' and one of the shorter female cultivars of winterberry holly, Ilex verticillata 'Red Sprite'.  I chose this sumac because it grows under a almost any condition, it only grows to about 3' tall and is a good choice for stabilizing slopes.  In addition it has a nice bright orange fall color and tends to be resistant to deer browse.  The female Red Sprite winterberry holly has a proper male mate in the nearby Jim Dandy.  I also transplanted in some extra black and brown-eyed Susans, Rudbeckia sp., to fill in around some of the newly planted shrubs.

As for flowering perennials, located 1-2 feet from the path, I chose foxglove beardtongue, Penstemon digitalis, short-toothed mountain mint, Pycnanthemum muticum, black cohosh, Actaea racemosa, and aromatic aster, Symphyotrichum oblongifolium. As the grass components I also put in some bottlebrush grass, Elymus hystrix, and wavy hairgrass, Deschampsia flexuosa.  I really like the looks of the bottlebrush grass and it is a species that commonly grows on the woodland edges in this area. Finally around the stepping stones and outer edges I put in the shortest species, two cultivars of moss phlox, Phlox subulata, and Pennsylvania sedge, Carex pensylvanica.

This is the completed installation.  I finished this in mid-July - later than is optimal for planting around here (mid-Jume would have been better).  I added in some old landscape timbers that were taken out from an earlier project to from the upper and lower edge of this garden.  Reusing materials on-site is part of being sustainable (and cheap).
As we are approaching fall the deer have come through and ate back the Penstemon and stripped most of the leaves and berries off of the holly.  I'm surprised about the holly, but our deer usually eat up most new plants no matter what they are, then leave them alone the following year.  Also the cohosh died back early, it may be getting too much sun, we'll see if it comes back next spring.