Vinca Replacement

Ever since we moved here 7 years ago I’ve wanted to replace the Vinca (V. minor) from our shady driveway turn-around.  Because I was new to the Mid-Atlantic area I didn’t want to do a wholesale replacement with something I wasn’t sure would work in this mostly shady, dry environment.  So I took a piecemeal approach, trying a little of this and a little of that, leaving most of the vinca in place.  This year I’ve decided to get more aggressive with the replacement, adding some successful species and trying some more new ones.

This was the next area for vinca removal.  It gets morning sun and open shade later in the day. 
It is framed on the right and left with test plantings of Heuchera and foam flower.

My primary reason for getting rid of the vinca is that it is an invasive species.  It is able to creep out of managed landscapes and run rampant in forested areas forming a dense ground cover that excludes native species.  From an aesthetic standpoint, while verdant, it can be rather boring and lack personality. Because of its ability to form thick foliage mats it tends to block out other less competitive species and creating a monoculture, at least on the ground plane.  

Most of the plants I have tried have survived the dry shade, but only a few have competed strongly against the viney invasive.  In all, I have tried nearly 25 native species in this area.  Strong competitors include Jack-in-the-pulpit (Arisaema triphyllum), green and gold (Chrysogonum virginianum), hayscented fern (Dennestadtia puntiloba), bigleaf aster (Eurybia macrophylla), Heucheras (I’ve had success with H. villosa and the cultivars ‘Citonelle’ and ‘Palace Purple’), twinleaf (Jeffersonia diphylla), Virginia creeper (Parthenocissus quinquifolia), zig-zag goldenrod (Solidago flexicaulis), merrybells (Uvularia sessilifolia), golden Alexanders (Zizia aurea), and the low-growing shrub sweetfern (Comptonia peregrina).  Also the non-native variegated Solomon’s seal (Polygonatum odoratum variagatum) is doing well (I imagine the larger native P. commutatum would also do well).  These are able to grow and spread without much help from me.  

Species that survive the conditions but need some help to keep from being overrun include wild bleeding hearts (Dicentra eximia), Alleghany spurge (Pachysandra procumbens), hoary mountain mint (Pycnanthemum incanum), smooth aster (Symphiotricum laevae), foam flower (Tiarella cordifolia), sedges (white-tinged sedge Carex albicans and pensylvanica, and there are some more robust wild ones like loose flowered sedge, C. laxiflora, that do very well).  Barren strawberry (Geum fragarioides, formerly in the genus Waldsteinia) should work well under these conditions, but in my case it seems to struggle.

Species that would be overrun without intervention include Meehan’s mint (Mehania cordata), woodland phlox (Phlox divaricata), and Labrador violet (Viola labradorica).  The only total failure was partridgeberry (Mitchella repens).  This tough little plant does not like to be covered, so between the vinca and the pine needles piling up it didn’t stand much of a chance. 

In this year’s planting I’m adding another sedge, ivory sedge (Carex eburnea), also wild geranium (Geranium maculatum) and, though I’m doubtful about this one, wild columbine (Aquilegia canadense).  I also have some downy wood mint, Bleiphila ciliata, which I started from seed that should do well in dry shade.

On the west end of this planting which gets a little afternoon sun, you can see the
ground hugging green and gold (now in bloom) and the much taller golden Alexanders (to the right).
Other plants include wild black raspberry, which appeared on its own, and several
volunteer trees that need to be pulled out.  

One of the features of vinca that is hard to copy with many native species is that it looks good (that is, pretty much the same) throughout the year with relatively little maintenance.  This is a great attribute from a design standpoint, but that does not make up for its invasive tendencies and relatively low ecological value.  Of the native species mentioned here green and gold and the sedges are evergreen (or nearly so) and the heucheras and foam flowers look good for most of the year.  Where there is sufficient moisture golden ragwort (Packera aurea) would be a very good evergreen choice.  

In the foreground you can see how Pennsylvania sedge pokes through gaps
 in the Virginia creeper (5-leaflets).  The sedge remains green throughout the year,
but looks a little ratty come January.  Another strong presence here is the zig-zag goldenrod,
with its ovate leaves, in the left and center of this image. 

Clearing this area took about 45 minutes.  Much of the time was consumed 
separating the vinca from the good soil after it had been pulled.  The pulled vinca 
was segregated to dry out and die before being put onto the debris pile.

Clearing the new planting space was surprisingly easy.  Since the area was thick layers of decomposed pine needles, the soil was very loose and most of the vinca could be removed with a 4-tine garden cultivator.  What didn’t come out with the cultivator was hand pulled.  I’m sure some bits of vinca remain and these will be addressed as they pop back up through the mulch.  I like using the fork because it hooked on the vines and it minimized damage to the deeper tree roots. 

Most of the new plants are in.  The most obvious are the heuchera and foam flowers. 
In addition to the wild geranium, columbine and ivory sedge are more
zig-zag goldenrod at the back of the planting and Labrador violets to the front edge. 
You can see the garden cultivator I used lying to the left.

Another means of vinca removal is cutting it back low then covering with a layer of cardboard, then mulch or clean soil.  This method would be better where the vinca is more firmly rooted.  I’ve tried spraying it with glyphosate, but the kill rate seemed rater low.

Here's the completed planting from another angle.  The new plants are mostly on the right edge
(see the little white tags?)  In the center of this view are established heuchera and foam flowers.

Using a variety of plant species in this area allowed me to tailor the planting to fit the variations in the site conditions: deeper vs. partial shade, arid vs. average moisture, etc.  Using plants with a tendency to spread both above ground, like foam flower and green and gold, or below the surface, like hay-scented fern helps cover the ground more quickly and allows the plants to migrate through the site to find their best conditions.  The variety also increases the biodiversity, extends the periods of bloom and provides more variation in form and color. 

I think for the next phase of vinca removal I will move to the middle of bed and try some taller species like the great Solomon's seal, white wood aster and more hay-scented fern.