Saturday, March 29, 2008

The Lahr Symposium: Cultivars of Native Plants

This Saturday the National Arboretum hosted the 22nd annual Lahr Symposium; the Lahr is a one day themed event that investigates some aspect of native plants. A good time was had by all, and we all learned something. Eight interesting speakers explored various aspects of the issue. Nine vendors participated in a sales area featuring the beautiful, the curious, and the obscure. All plant people are covetous and I am as lustful as the next man; for the bog I bought Acorus americanus, iris versicolor, Caltha palustris, Hypericum densiflorum, and a combination pot with Venus-fly trap, Sundew, and Pitcher plant. For the open garden, Rhapidophyllum hystrix, Rhododendron cumberlandense and Rhododendron austrinum an orange form. For the landscape crew I bought another Needle-palm.

In his talk,Tony Avent, owner of Plant Delights Nursery, and possibly the country's preeminent horticultural lecturer, spoke for the affirmative, enthusiastically endorsing the use of cultivars in a wonderful talk lavishly accompanied by awe-inspiring slides showing examples of extraordinary selections of native plants. Dr. Michele Dudash, a professor of evolutionary biology at the University of Maryland responded, not negatively, but with some cautionary observations. She reminded us that simple Mendelian genetics dictate that one of the basic tools for developing culativars, "selfing" (crossing a plant with its genetic homologue), produces a generation with half the genetic variety that would have resulted from an open cross. She explored the literature on the effects associated with planting cultivars in reproductive range of their parent species and it turns out there are effects. "Horizontal" genetic exchange occurs between the two groups ; "vertical" movement of those genes into the progeny of the native population does result in the adjoining population of native plants becoming, over generations, more "like" the cultivars thus decreasing diversity. Further, she noted that often the features that increase the appeal of a plant to us, double flowers for example, may directly correlate to a loss of nectaries, or stamens (because they were transformed into petals) and so decrease pollination or genetic exchange. Decreasing the genetic diversity in a species makes it less adaptable and more vulnerable in general. Apparently we ought to be careful when we make decisions about what to plant where which is, I guess, no surprise to anyone. But we still all want Tony's plants.

Good speakers, good plants, and the Arboretum was, and is, beautiful. Magnolias, Cherries, Flowering apricots, and a host of early spring flowers make this a "must visit" week for Washingtonians and visitors. Thank you, Joan Feely, the Curator of the Native Plant Collection, who has been responsible for the Lahr for almost as long as my adult sons have been alive. Sorry Joan.

Friday, March 28, 2008

On the Purpose of Gardens w/ Before Photo

This week, Karen and they boys have been installing a design on Capitol Hill; for the area, it is a pretty good-sized corner lot. One of the owners sent an email yesterday to tell us how pleased were and how wonderful it was to come home from work every night and find new things......Hey thats what gardening is about. And spring. You don't have to install a new plant every day to be able to regularly have something new happening! The garden does the work.

The plant list for this garden ran to two pages of smallish type so there are a lot of taxa and much diversity of form, texture, size, color, seasonality; there are flowers most of they year, potentially all year if this winter repeats itself. There are evergreens with and without winter color. There are grasses with winter presence. There is a wide range of flower form and color. Even in the middle of the city, with the aid of their small pool and diverse plantings, they ought to be able to attract an interesting insect flora: dragonflies,damselflies, butterflies, fireflies, ladybugs, moths. I hope there is enough time in their lives to slow down and appreciate what they have done.

Tuesday, March 25, 2008

Corylus avellena contorta 'Harry Lauder's Walking Stick'

Everyone who sees this plant's silhouette in the winter or its catkins expanding in the spring needs to have it. It is truly spectacular. The weeping contorted branches often recross, occasionally grafting themselves together producing fantastical constructions . Wayside Gardens, long ago, maybe in the late 1960's or early 70's ran a page in their catalog with two picture of plants in the snow; this plant and Cornus alba siberica , a red-twigged dogwood. I expect they sold a lot of these combinations; I know my parents bought one. I planted their walking-stick at the top of a terraced wall that I had made for them. Shortly after moving to Adelphi, I planted a small walking-stick above the wall in the back garden. Today it is 8' tall and an irreplaceable fixture in our garden.

Back in the day, this plant was available only grafted; every year I spend too much time cutting off suckers from the rootstock. On more than one occasion, I remember going on a design appointment and meeting a walking-stick that had been completely overgrown by root suckers. I cut then away, to he horror of the plants owners, and the small contorted shrub that remained was freed for a while. I strongly recommend buying it on its "own roots", as many are grown this way now. While I have never been seconded on this opinion, it seems to me that the "own root" plants are more contorted. I think that this is because the extra vigor provided by the stronger rootstock allows for more cellular elongation when new growth is made and therefore more straight lengths....Of course I could be wrong.

The big negative issue with this plant (that is more than overbalanced by the positives) is that, it is a liability in the summer. Japanese beetles skeletonize the leaves and it is a fright to behold from June until it defoliates. This doesn't mean you can't have it; it just means that it needs to be sited where you can appreciate it in the winter and ignore it in the summer. It is a bonus if the sun shines through the catkins in the morning or late afternoon in the spring, but the catkins are so outstanding that it will draw your attention from anywhere.

Planting Project at the Capitol Columns

Monday is project day for the gardeners at the National Arboretum, and yesterday we planted several thousand perennials at the Capitol Columns: 40 flats of Amsonia hubrechtii, narrow-leafed bluestar, and 32 flats of Schizachryum scoparium, little bluestem. Both of these plants are natives of the Eastern United States, and both have great fall presences.

When the planting is completed it will contain 3 taxa this year, and two henceforth. We planted two perennials and will later plant an annual grass from South Africa, Melinus nerviglumis Pink Crystals. A hot season grass, Pink Crystals, will help fill in the planting until the Amsonia and Schizachryum, mature.

In an effort to "randomize" the effect, we started by "tossing bunches of the plants into the air. If you maximize the picture, or have really good eyes you can see the plugs distributed (thrown) over the area waiting to be planted. Some rearrangement was necessary but I think the effect is good overall. It will be fun to watch the small plugs grow into mature plants.

Monday, March 24, 2008


I have a love/hate relationship with this Clivia. It is beautiful but it is heavy and it has just reached its peak bloom, so it is at its best just when our focus is shifting to the outdoors. I do love it but every year I decide to break it up and give away the pieces! But this year probably won't be the year! It flowers best crowded and it can last one more year before it will need to be divided.

As soon as there is enough foliage on the dogwood to provide shade, it will go out for the summer. It starts out in the bright shade and at some point towards the middle of summer, I move it out into "full sun", which means in this case, 6-7 hours of direct sun. It can take a few degrees of frost, but it comes in, usually in mid-late October when the forecast calls for temperatures to fall below 30F. It spends most of winter in the unheated portion of our basement with very few waterings; it is going through a dormant period after all (if you can't provide a cool period it will flower anyway but be sure to cut back drastically on watering to enforce dormancy). When I notice the flower buds deep in the leaf bases, I bring it upstairs and it flowers nicely.

While this is the old fashioned orange Clivia miniata, there are a variety of other species and selections available. Some are Yellow flowered, some a bit smaller (which would be nice), and some with variegation in the leaves. Choose carefully, this plant will never die from neglect so you are choosing a life companion! Every few years its thick roots will literally force their way out its pot, deforming plastic and breaking terra-cotta or ceramic. Then its time to divide; discard 2/3 (or give the divisions away), re pot, and you're good for another 4-5 years.

Sunday, March 23, 2008

Defining Space in the Garden

This tree, a Fullmoon maple, Acer japonicum, outgrew its barrel last year so I planted it in the ground. Sitting just north of our kitchen window the buds catch the rays of the rising sun coming from the right. Looking at, or more accurately, through the buds, forces us to orient ourselves. The buds themselves are spatially disposed in a pattern determined by the genetics of the plant and its interaction with its environment. As we move and our viewpoint shifts, the buds move in relation to each other making us acutely conscious of our location and our proximal relation to the plant. Hey, try it! Its easier to see than to explain. At least for me!

We don't normally choose plant material for its buds, but if winter interest is important, as it is in highly visible locations, having interesting buds can be a factor in our selection. The buds of the more common Japanese maple, Acer palmatum, and its innumerable cultivars are attractive but lack the size and the white hairs of these buds, and for that reason the Full moon maple is sometimes a better choice.Other plants that display this wonderful three dimensional array of buds include flowering dogwoods and many deciduous azaleas.

This is one of many many things to consider if you are designing or redesigning your garden. An analogous definition of space can be done with plants that have horizontal saucer shaped inflorescence (flat heads, like lace-cap hydrangeas for example). Planted alongside a path that changes elevations, our changing view of the flat flower-heads emphasizes our vertical movement.