Living Mulch

Mulching garden beds has been a consistent ‘must-do’ for many gardeners.  Mulching reduces moisture evaporation, suppresses weeds, adds nutrients to the soil, reduces erosion and in many cases improves moisture absorption. Wood and bark chips are the most common materials employed.  Recently I have seen and read more about the negative effects of wood chip mulches. In particular when these mulches are over applied and allowed to compact, they can actually retard rain water absorption.  Thickly applied mulch can retard the growth and expansion perennials.   In his book The Know Maintenance Perennial Garden, Roy Diblik discusses how unnatural wood chip mulch is.  In areas that get adequate rainfall to support a tight matrix of plants, a living, or green, mulch is the ideal.

For many sustainable and naturalistic gardens the goal is to create this ‘green mulch’ or ‘living mulch’ by filling the space between garden features or larger plants with more plants.  ‘Green mulch’ is living plant material that performs all the functions of wood mulch such as weed suppression and soil moisture and temperature moderation.  In addition properly selected green mulches offer additional benefits like supporting wildlife and insects with food and cover, lower maintenance (since they do not to be replenished or broken up on a regular basis).  This green mulch may be a single species or a variety of plants that form an interlocking matrix. This matrix is most like what you would encounter in a meadow or woodland setting.

An example of a classically mulched bed. 
Each plant is distinctly identifiable and  there are no
random plants to confuse the composition.

One problem with green mulches is that they can look weedy due to lack of readability, no clear design or cluttered appearance.  Many folks are more comfortable with a landscape or garden where the features are clear and recognizable.  Having beds with clean edges is a quick way to make a garden more legible.  This human desire for legibility is also seen in the preference of many for plants neatly separated by oceans of mulch. 

One means of creating a green mulch is to install plants closer together so that they quickly grow together to create a continuous green carpet of foliage. This is one of the themes of the book New Naturalism, by Kelly Norris, published in 2021.  The trick here is to create plant communities that a good match to your site conditions and that the plants play well together. 

An example of a green mulch.  Creeping phlox, Phlox subulata,
and wild strawberry, Fragaria virginiana, have grown together
 to form a 4-6" deep ground cover.  Shrubs and perennials,
like the wild geranium, Geranium maculatum, here,
 are able to grow through.

Another route to a green mulch is to plant lower grow species as a matrix between your feature plants.  The trick here is to keep your garden readable so that the matrix does not obscure your design intent.  By way of example consider what bindweed does to a garden.  While it grows quickly to fill all the voids in the garden it also grows up and over taller plants resulting in tangle of plant material that has no discernible form, no starting or ending points and little textural contrast. (Kudzu does this on a much larger scale, draping a woodland edge with green vines, effectively removing all contrast between the trees.)  Consider instead a perennial bed where the spaces between plants are filled with low growing violets.  The glossy round leaves of the violets don’t interfere with the forms and textures of taller perennials or shrubs.  A list of some of the lowest growing  Mid-Atlantic natives includes:  Pussytoes (Antennaria sp.), wild ginger (Asarum canadense), Green and Gold (Chrysogonum virginianum), wild strawberry (Fragaria virginiana), barren strawberry (Geum fragarioides), Meehan’s mint (Meehania cordata), partridgeberry (Mitchella repens), golden ragwort (Packera aurea), various species of phlox (Phlox divaracata, stolonifera or subulata),  foamflower (Tiarella cordifolia), common violet (Viola soriana),  and  short sedges like rosy and ivory sedge (Carex rosea  and  C. eburnea ).

Golden ragwort is excellent native ground cover.  It spreads rapidly
 in moist, partly sunny locations.  It also seems to suppress invasive
 weeds like Japanese stilt grass and garlic mustard.

 

Using spring ephemerals for this purpose is a very natural means of creating a matrix.  These perennials naturally flourish early in the year when tree and shrub canopies are open, then slowly go dormant as the canopy closes up.  They return again the following spring.  In the Mid-Atlantic you may find Dutchman’s breeches and squirrel corn (Dicentra sp.), mayapple (Podophyllum peltatum)  and Virginia bluebells (Mertensia virginiana)  as common examples of these.  A limitation with using ephemerals is that they do totally disappear after setting seed.  They are ideal in an established perennial or shrub bed where you just need something in early spring while the larger plants are leafing out.  

Ephemerals, like cutleaf toothwort, Cardamine concatenata (in bloom),
 and Dutchman's breeches, Dicentra cucullaria, fill out in early spring.
but disappear as the tree canopy fills in. 

Using short-lived species that survive primarily by reseeding is another means to establishing a sustainable living mulch.  By nature these are opportunistic gap fillers.  As the longer lived perennial and shrub layers get established these reseeders tend to be squeezed out as their preferred, open habitat disappears.  Yellow fumewort (Corydalis flavula), American pennyroyal (Hedeoma pulegiodes), common yellow woodsorrel (Oxalis stricta), and self-heal ( Prunella vulgaris) are some of the shorter species that can be used in this way.  Taller, showier species that can be used as temporary gap fillers include wild columbine (Aquilegia canadensis), Partridge pea  (Chamaecrista fasciculata), fleabanes (Erigeron annuus and E. philadelphicus), and black-eyed Susans (Rudbeckia hirta).

Wild columbine, growing about 2' high, is relatively
 short lived in gardens due to competition and rich soils.
It produces a lot of seed so that it can reappear in other suitable
 locations where seeds can make soil contact and
have access to sunlight. (unmulched areas).

Yellow wood sorrel is considered a weed in many cases.  However,
 this native plant satisfies the requirements of a living mulch quite well. 
It grows quickly and produces lots of seed to fill gaps, is relatively short lived,
and is easily displaced by larger plants. As a native it also supports wildlife,
 particularly bees and birds.  Its lax, floppy habit detracts from it appearance,
making it appropriate around much larger plants and shrubs
or where this flop is not a distraction.

Oxalis stricta is very similar to its European relative, O. europea. 
Each has the same common name, common yellow woodsorrel. 
The North American species can be distinguished by the horizontal
disposition of the seed stalks (indicated by arrow). 
O. europea has seed pods on ascending stalks.

So if you are willing to give up the repetitive chore of mulching your garden beds, consider having your plants do that job for you and establish a living mulch.

What worked in 2016

Looking back on how my plans for incorporating the new native plants worked this past year revealed more successes than failures.  Here's a rundown on what worked, what didn't and what I learned.

Plants from seed
Probably my best result came from seed for rose verbena, Glandularia canadensis.  After about 6 weeks of cold stratification I had very good rates germination after a week under lights.  I didn't see any plants from direct seeding outside done at the end of February.  Either that wasn't long enough or the conditions just were not right.  Surpizingly the plants are still leafy green outside (we are on the border of zones 6 and 7).

I also had good results with the annual Texas sage, Salvia coccinea, after a month of cold moist stratification.  We also had a lot of these coming up in pots that had been stored in an unheated garage, but none from seed that was left outdoors.

 The failure here was with Indian blanket, Gaillardia pulchella.  This one germinated during stratification.  I planted the sprouted seeds, but they were weak and didn't amount to much, even after being potted up.

Rose verbena was blooming by mid-July
and continued through the summer.  

This American bellflower is a favorite of native miner bees. 

A biennial that is really happy here is American bellflower, Campanulastrum americanum.  I started a few from seed in 2013 and now have volunteers scattered around the flower beds.  Another name for this species is tall bellflower; mine typically reach 4-5 feet when in bloom.  The deer browse on this a little early in the season, but tend to leave it alone after July.  It can get rather lanky, so it is best toward the back of a border or in the shade where it does not get so tall.





New Perennials

The white flowers of wild strawberry are another way
to distinguish it from mock strawberry, which has yellow flowers.

Since I was seeing good results from a hardy cultivated strawberry from the local master gardeners I thought I would try out some of the native species, wild strawberry, Fragaria virginiana.  Planted in mid-spring, these small plants settled in enough to put out runners to start new plants a foot or two away.  Got some flowers but no fruit this first year.  Looks promising as a fruit-bearing ground cover for next year.

These white woodland phlox, growing in my woodlands
are similar to ones I transplanted to under the pines.

I also planted both woodland and creeping phlox, Phlox divaricata and P. stolonifera, in open shade under some pines.  This is an area where I am trying to replace a mass of vinca.  These species do well in the shade of deciduous trees, we'll see how they handle the consistent dry shade of evergreens.  The woodland phlox that I planted in the spring disappeared in the middle of summer but put forth new growth in the fall.  The creeping phlox, which is more tolerant of dry soils, was planted in the fall.  We'll see which of these two species is more successful here.

In this same pine-rich area I added more Foamflower, Tiarella cordifolia, and hairy alumroot, Heuchera villosa, as seedlings.  In general the Heuchera survive these conditions much better than the Tiarella.  It was probably too dry for the young plants to get established.  While the Heuchera grow better, they are also more subject to browsing by critters, deer or rabbits of both.  Next time I get some Tiarella I'll try it in a moister location, perhaps under a walnut tree.

The flowers of blunt mountain mint are very attractive to pollinators.

A new native I added to the garden was blunt mountainmint, Pycnanthemum muticum.  I had been trying out hoary mountainmint, P. incanum, for a couple of years.  Planted in a partly sunny location, it has been rather slow to grow.  I planted the blunt mountainmint in a slightly sunnier location nearby and it grew to about 2' and was covered with dense pinkish flowers.  As showy as the flowers are the silvery bracts at the base of each flower.

I have been trying to get some blazing star, Liatris sp., to grow for several years.  It seems they get started, then disappear.  I'm pretty sure I'm losing them to some small mammals, ground hogs or rabbits.  This year I tried plains blazing star, L. squarrosa, with mixed success.  The ones planted in the open disappeared, while the ones surrounded by other plants were able to survive.  We'll see if these can get established.

Plains blazing star in bloom.  This species has
button-like flowers rather than spikes

Another regionally native plant that didn't bloom but seems to be getting established is vasevine, Clematis virona.  I didn't notice them much during the growing season, but when I cheked for them this past week I did find that the wiry vines had grown several feet.  I hope I can share some photos of its bell-shaped flowers next summer.


New Shrubs

This gray dogwood managed to bloom before it got pruned back by deer.

My main 'reclaimation' project last season was to displace invasive wineberry, Rubus phoenicolasius, and Japanese honeysuckle, Lonicera japonica, from a steeply sloping hedgerow.  I don't want to destabilize the slope, so I have been cutting back the invasives and treating the stumps with herbicide.  In 2014-15 I put in some smooth sumac, Rhus glabra.  This year I added gray dogwood, Cornus racemosa to the top and middle slopes and American hazelnut, Corylus americana, to the shadier lower slope.  Most of these were planted bare root in the spring and they seem to have survived their first year.  The biggest challenge for the dogwood is deer browsing.  This was also a problem the first year I planted red osier dogwood, C. sericea, but after a year the deer seemed to lose interest.  I have read that deer will browse more on new plants, especially those from a nursery, because their leaves are more tender and they are higher in nitrogen.  After the plants settle in, the leaves toughen up and become less appealing.  I hope it will be the case here.

On a disappointing note, only one of the five bare root red cedars, Juniperus virginiana, survived.  I have my lone survivor surrounded by chicken wire to protect it from deer.  I'll probably need to keep it caged up for a few more years, especially during rutting season.

Now its time to start planning for next year.  Let's see, what should I get????

Which is the Strawberry?

I am adding a number of Virginia strawberries, Fragaria virginiana, to my gardens this year.  This is part of my plan to incorporate more edible plants, particularly natives, into the landscape.  While I may not get many berries from these little plants this year, I expect to get a harvest next year after the plants have settled in.  One important thing that I will need to learn is how to tell these fruit bearing plants from the insidious mock or Indian strawberry, Duchesnea indica, that is growing just about everywhere on the property.

Here is mock strawberry with its bright yellow flower
and trifoliate leaves.  These leaves are evergreen here in zone 6.

Indian strawberry is an exotic species from southern Asia imported to the US as an ornamental plant and has widely naturalized over the years.  The 'Indian' in the name refers to a region of Asia, not Native Americans.

Both plants have similar trifoliate leaves with bluntly serrated (toothed) edges.  They each form tight clumps of basal leaves, spreading by above ground runners.  Also, they each produce bright red fruits with seeds on the surface.  The most obvious difference is the flower color, Virginia strawberries have white, 5-petaled flowers, while those of mock strawberry are bright yellow.

This newly planted Virginia strawberry has not settled in enough to flower.
The leaves are persistent through the winter, but these will turn red,
adding to winter interest.

Another difference is in the fruit.  The seeds of Virginia strawberry are located in depressions on the surface of the red 'berry'.  Mock strawberry seeds are actually in projections above the fruit's surface.  Also the fruit from mock strawberry is dry and tasteless compared to the sweet, juicy fruit from the Virginia strawberry.


These differences make it easy to tell the two plants apart when they are in bloom or fruit, but what about the rest of the year.  I was looking for a definitive feature to rely on.  Many times botanical descriptions depend on doing a comparison, e.g. more or less hairy, or 'broader' leaf.  I was looking for a yes or no test that I can use quickly while pulling weeds.

Here are both surfaces of the leaves of mock strawberry.
The arrow at left points out the longger terminal tooth.

So while the leaves of mock strawberry are more coarsely serrate and its veins are more divided than those of Virginia strawberry, the more practical method for me is to look at the tip of the leaf.  On nearly every leaflet of mock strawberry the  terminal tooth is longer than the ones on either side.  For Virginia strawberry the terminal tooth is shorter the its neighbors.  Maybe after working with the Virginia strawberries for a season or two I will appreciate the finer differences.  For now the goal is to not pull up any of my new plants.

Here are both leaf surfaces of Virginia strawberry.  Again,
the arrow points to the terminal tooth on the leaf, which is
distinctly smaller than its nearest neighbors.

New Plants for 2016

As we are approaching another planting season I've come up with a list a new native plants to add to our landscape.  Most of these plants are to build on the existing communities.  My main goals are to  provide food for wildlife, displace invasive species, stabilize soils and add visual appeal.  To help me determine what is native here near the Potomac River, I am using a guidebook from U.S. Fish and Wildlife Service for most of my plant selection.

One area, shaded by white pines and red cedar, is densely populated with Vinca minor.  I trying to get rid of that and replace it with a variety of shade loving native species.  I am having some good success with green-and-gold, Chrysogonum virginianum.  It is filling in nicely with a dense mat of evergreen foliage.  Foamflower, Tiarella cordifolia, is spreading slowly, so I will be adding more of those to give them a boost.  I brought some hairy alumroot with reddish leaves, Heuchera villosa var. atropurpurea, from my Boston garden and it has survived well.  When I saw it offered by Prairie Nursery I ordered a bunch more.

Here's a mixture of seed grown Heuchera villosa, both green and red-leaf forms.

This woodland phlox grows all around our property,
mostly in the shady woodlands.

I will try adding some woodland phlox, Phlox divaricata, to the mix this year.  It's growing wild nearby, so it will be a truly natural extension into this space.  I thought that this needed moist conditions to do well, but I read somewhere that it could also grow in drier shade conditions.  We will see if that's true.

One species that is not native to this region that I am trying out this year is rose vervain, Glandularia canadensis. It is a native groundcover from the Mid-West and South.  It is a perennial in warmer areas, but otherwise it's a reseeding annual.  I was inspired by the cultivar 'Homestead Purple' that is heavy blooming and hardier than the species in cooler climates.  Rather than buying the individual plants of the named cultivar, I decided to start some from seed.  These plants won't necessarily be the same, but I'll get a feel whether I like it enough to invest in the cultivar.  Deer and rabbits like these too, so we'll see if any survive.  If successful, these would be a nice ground cover to use around shrubs in sunny locations.

I would like to establish some Liatris in our gardens.  The mid-summer blooms are very popular with a variety of pollinators.  Unfortunately, the spike gayfeather, L. spicata, that I've planted has also been popular with our rabbits and/or groundhog.  This year I will try adding scaly blazing star, Liatris squarrosa,  This species is native to the nearby Piedmont region of Virginia.  Maybe its rougher texture will be less palatable with the local herbivores.

Another new addition to the garden will be vasevine, Clematis viorna.  The purple bell-shaped flowers appear in mid-summer.  I will plant these along a fence in open shade/part sun and mesic soil. I planted virgin's bower, C. virginiana, this same area area several years ago and it has taken hold quite well.  If all goes as planned, as the vasevine flowers finish blooming the virgin's bower will kick in.

I am trying out Bushy St. Johnswort, Hypericum densiflorum, for a second time.  I was unsuccessful past, but that was in a fairly shady location.  This time I'll give it more sun and a more consistent supply of moisture.  If it finds this a suitable spot, it is supposed to spread thickly.

As I mentioned in my last post, I am removing invasive plants from a hillside hedgerow and replacing them with natives that spread out forming clonal colonies.  These clonal shrubs will help hold the hillside against erosion.  The two species I'm adding this spring are American hazelnut, Corylus americana, and gray dogwood, Cornus racemosa.

In addition to the soil holding properties, American hazelnut also produces edible nuts
that benefit wildlife, or humans (if we can get them).  In this photo
you can see male catkins emerging above the dried leaves.

Gray dogwood  has small white flowers on terminal racemes
in late spring.  After foliage drops in the fall the shrub is distinguished
by the few remaining white berries on  bright red stems.

At the end of March the lowbush blueberry flowers were just beginning to open.
 No flowers yet on these cultivated strawberries.

Two years ago we planted several native lowbush blueberries, Vaccinium angustifolium, and some cultivated strawberries that I got from a Master Gardener sale along the walk to our front door.  These have performed quite well and are beginning to spread.  Since I am all about native plants, I will be adding some of the native Virginia strawberries, Fragaria virginiana.  This species is one of the two originally hybridized to create the modern cultivated strawberries we all enjoy.  Though small, the Virginia strawberries are packed with flavor.

Got these as bare root plants and potted them up until
the meadow gets its annual mowing.

I never thought I would need to but I am adding some eastern red ceder to the meadow along its wooded edge.  I would like to have a few evergreens growing in that area.  There were some indigenous seedlings, but they disappeared.  I fear the deer have chewed them to the ground.  I'll put some cages around these for a couple of years.

Now I just need to get to work!