Mind Your Matrix

As gardeners, we all have our favorites. I hate houseplants, I like trees, I love shrubs, but I’m absolutely mad about herbaceous plants. Perennials, grasses, ferns and sedges have been a sustaining passion for most of my gardening life, and I see no signs of the fever breaking. There’s something about the way they change daily, completing an entire cycle of emergence, growth, maturity, decline and dormancy in just one year, that’s always fascinating, exciting and touching, really… a metaphor for the human condition.
 
For the last couple of years I’ve been doing speaking gigs at some local garden clubs, plant societies and the like, introducing home gardeners to the new way of using herbaceous plants. This type of planting has been called, most often, the Dutch Wave, and it’s been lapping at our shores for twenty years or more. Now it’s gained enough attention, through publicity and exposure of plantings like New York’s High Line, to pique the interest of the general gardening public. Everywhere I’ve presented, interest has been high, and there are lots of questions about how it’s actually done.
 
I’m far from an expert on naturalistic planting, but like many seriously addicted home gardeners, I’ve started to experiment with these concepts on my own property. My venture is a wet meadow triangle of approximately 4500 square feet. Partly shaded, it’s the lowest corner of our property where everything drains, and was always a pain to keep mowed. Because the initial outlay on this type of planting is considerable, from both a budget and a labor standpoint, I divided the project into three sections. Last year I planted the first section, this season the second, and the third section is being prepared for planting in 2020.

The first section is only in its second summer after planting, but as you can see it’s filled in very densely. Weeds haven’t been much of a problem at all, after an initial going-over in late spring. There’s tweaking to be done, and there were some holes to repair where grasses drowned after our extremely wet fall and winter, but overall everything has taken well and is flourishing.

Naturalistic planting is all about choosing the right plants for your site, not trying to alter your soil and conditions to suit an arbitrary list of plants you’d like to grow. It’s the old adage of “right plant, right place”… the commonsense notion that a plant will thrive in the conditions it has evolved to grow in. This means natives, of course, but also non-natives from similar ecosystems in other parts of the world.  So I had to call on all my experience, and do some homework, to assemble the list of plants for this area. Included in the first section are (more or less left to right above), Monarda ‘Raspberry Wine’, Panicum ‘Hot Rod’, Molinia ‘Skyracer’, Heleniums, Scutellaria incana, Persicaria ‘Firetail’, Geranium wlassovianum, Veronicastrum virginicum, Eutrochium ‘Gateway’, and Carex muskingumensis.

If you’ve read anything at all about naturalistic planting, one term you may have encountered already is “matrix”. The idea of matrix planting is to combine three or four plants of similar requirements and relatively equal vigor (this is critical) so that they knit together and function the way ground covers have been used in the past. This “living mulch” covers all areas not occupied by larger, taller perennials and shrubs, so moisture is conserved and there is no space for weeds to gain a foothold. I took the photo above on the High Line last September, showing a mature matrix planting of Sporobolus (Prairie Dropseed), Sedums and Euphorias, through which the taller plants, like the orange Butterfly Weed, can emerge.

It’s a concept that works, but the trickiest part is figuring out which plants will suit the purpose. Many of the things that serve well in this capacity aren’t commonly available in nurseries. But the good news is that you might already have some of them, like Ajuga, Common Violet, or Creeping Jenny. Even quite thuggish plants can be employed here, if they’re balanced with equally aggressive companions, like the matrix above at Federal Twist, James Golden’s inspiring garden in SW New Jersey.  The combination of Equisetum, Ajuga and Creeping Jenny is obviously not for every situation, but it works in this large, moist, densely planted garden.

Another matrix planting above, this one also at Federal Twist, of Persicaria bistorta, Sensitive Fern, and Equisetum. In their essential book on naturalistic planting design, Planting In a Post-Wild World, Thomas Rainer and Claudia West call this matrix the ground cover layer, so you will hear different terms for this undercarpeting, but the idea is the same: plants become the mulch.

Back at my place, I’ve planted up the matrix above in section 2, installed this spring. A trio of Mountain Mint, Wild Ageratum and Palm Sedge is already growing in nicely. Achieving quick density is key here… rather than planting with 1- or 3-gallon plants spaced 18” apart, the ideal is to use small divisions or landscape plugs planted just 6 to 9” on center. Getting everything to grow together as soon as possible creates a tapestry of vegetation that functions as a stable, ongoing plant community. At least that’s the goal… it remains to be seen whether my choices will balance each other out, or whether one of them will overwhelm the other two. But it’s all an experiment, and it’s just gardening after all, not open heart surgery.

Here you can see a taller plant emerging from the matrix, in this case Eutrochium ‘Baby Joe’.
As in nature, larger plants will have no trouble pushing up through a well-designed matrix, and their deeper root systems mean that they occupy different strata both above and below ground.  But what about my annual mulching, you say? After the planting knits together, in a couple of seasons, you can forget about the mulch and put your efforts (and your mulch budget) elsewhere. There will be surprisingly few weeds cropping up if you’ve chosen the plants appropriate to your site’s conditions, and planted them at the proper density.

You can also use just one plant to provide the ground cover layer. Here, in the shadiest part of my section 1, Packera obovate fills in by offsets and by seeding in, carpeting the ground around the larger plants like Iris ‘Gerald Darby’ and Angelica gigas. Packera obovata isn’t as popular as its relative, Packera aurea, but having grown them both I much prefer obovata… smaller, glossier and tidier foliage, with more compact flowering in late May. In another adjacent section I used common Violets, dug from our lawn (free!). Sensitive Fern works well too, and most of us have it somewhere on our property if conditions are naturally moist. There are no rules… one has to think these things up, as Little Edie said.

Once you understand the matrix concept, you can apply it to any conditions in your garden, whether it be shady, sunny, moist or dry. Here, on our hot, dry and sunny terrace beds, I’ve used low carpeting Sedums, Veronicas, Creeping Phlox and the like to create a matrix through which grow grasses, Lavenders, Alliums, Pulsatillas, and early species Tulips.

If you don’t want to be quite so formulaic about using a matrix, you can get the same weed suppressing and moisture conserving benefits by planting grasses, perennials and even annuals very densely and allowing them to grow together into a tapestry of herbaceous vegetation. That’s the philosophy at the wild and wonderful garden of Jack Potter and David Lebe, in nearby Harlemville, NY.

Their sun-drenched hillside is on the dry side, but there wasn’t a wilted leaf in sight on a blazing hot Open Day a couple of weeks ago. With their vast plant knowledge, and through trial and error, Jack and David have assembled a plant palette that’s perfectly adapted to thrive in their conditions. Natives are a high proportion of the mix here, but by no means are they the only plants allowed.

There is no lawn, no sprinkler system. Just gravel paths, stones and plants… lots and lots of plants. Anyone interested in naturalistic planting should really make an effort to see this garden when it’s on Open Days. To wander here among so much color and texture is inspiring and enchanting, a real testament to two masterful plantsmen who are unafraid to let plants be plants.

Let me state, without judgement, that this kind of planting is not for everyone. Many people think it looks “messy” or “weedy”. There is unquestionably a higher proportion of green leaf to flower color for some people’s taste, because there is no attempt to have everything flowering at once, or continually. The idea is a progression, over a long season, where two or three or four plants make a show while others are waiting to bloom or have already passed into an attractive seed stage. And the colors and texture of foliage become as important as the flowering. The garden above, in Kinderhook, NY, might look unkempt to some, but I much prefer it to the typical lawn, foundation shrubs, and groundcover of Pachysandra or Vinca.
 
One of the things I point out in my talks is how, over the arc of my gardening life, tastes and interests have evolved. No longer do we care only about masses of color and traditional perennial borders that are relics of an era when maintenance labor was cheap and plentiful. Now we want manageable, sustainable plantings that require less weeding, mulching, staking and deadheading. And we want more natives, more plants that nourish pollinators and beneficial insects, feed and shelter birds, and in general make more of a contribution to the web of nature. This is particularly true of the younger gardeners I meet. But those of us who have a lifetime of experience can be at the forefront of this quiet revolution, using our hard-won knowledge of plants and their requirements to assemble successful and beautiful planting schemes that satisfy, both aesthetically and ecologically. I challenge you to that goal… I think you’ll find it fascinating and very rewarding.