Garden Notes: Mahonias

A fragrant ray of sunshine among the brown oak leaves.

A ray of solstice sunshine: Mahonia x media ‘Charity.’ — Susan Safford

Winter is here. Overnight, privet hedges assumed their cold-weather maroon coloration. Driving home at twilight, it is dancetime in the headlights for male winter moths (the females are flightless), starring in their annual fluttery showtime. Does snowfall impede their reproductive success? I hope so.

Now that snow becomes a reality, it is prudent to look at English ivy tangles in trees. Not so much in the traditional carol’s sense, “the holly and the ivy, when they are both full grown …” — though that is a timely trope — but in the gardener sense, of tree care and concern.

While a tree that is covered with ivy may be picturesque, it is already at risk: losing light needed for photosynthesis to the smother of top-heavy ivy foliage. An ivy-infested tree in snow and ice is carrying a double risk, the ivy’s and the snow’s weight, and is prone to toppling. Pull the ivy off trees you care about before winter is fully upon us, especially if it is reaching up into the crown, or snow and ivy may instead pull the tree down. This applies to top-heavy, ivy-clad fencing as well.

While on the subject of ivy, a side observation is the unusual numbers of English ivy seedlings that we are spotting in beds and hedges, which suggest that much ivy is running wild and forming fruit. When the plants are able to climb, they morph into a different, adult form, producing a differently shaped leaf, flowers, and berries.

Ivy is customarily viewed as an eco-resource in the British Isles, where it is native. Here it is more recently designated as “invasive alien,” although the berries sustain our birds as well as they do the British ones, judging by these seedlings.

Winter interest: Mahonias

A while back I wrote here that I intended to create a row of mahonia in my woodland garden. I am closer to the goal with Mahonia x media ‘Charity’ and x Mahoberberis aquisargentii, an intergeneric hybrid mahonia. The two mahonias are underplanted with epimediums; both mahonia and epimedium are in the Berberidaceae.

In attempts to trounce winter and broaden the range of plantings, gardeners in this climate eventually arrive at developing winter interest, if not an outright winter garden. Conifers, broadleaf evergreens, evergreen groundcovers, berried plants, plants with colorful twigs and beautiful bark: the list is more extensive than one might suppose when taking a cursory look at the wintry scene.

What could be a more spectacular addition than mahonias? They seem to be underused and underappreciated. The hybrid mahonia pictured, ‘Charity,’ is a fragrant ray of sunshine among the brown oak leaves. The deep green, leathery foliage, spiny like a holly simulacrum, reflects the low solstice sunlight, and the racemes of tiny flowers are full of nectar for an insect, should any be about now.

Polly Hill Arboretum’s collection contains five mahonia species in nine different locations that you can check out. According to Roy Lancaster’s comprehensive mahonia article in the December 2012 issue of the Royal Horticultural Society’s Garden magazine, mahonias mostly divide into autumn-flowering and winter- or spring-flowering. ‘Charity’ belongs in the former category. The Mahonia x media hybrids, which also include ‘Winter Sun,’ ‘Buckland,’ and ‘Lionel Fortescue,’ respond well to hard pruning immediately after flowering. Lancaster advises, “The larger Asian mahonias and their hybrids have a dense, hungry root system, growing best in fertile soils, acidic or alkaline, and mulching with organic matter such as garden compost.”


Worthwhile trees

I get around parts of the Island a lot, and look intently at many plantings and landscapes, in addition to those we work in. Nonetheless, it would seem that consciousness concerning good trees has not been raised much since Polly Hill was beginning to plant in North Tisbury and becoming tired of the thin selection of plant material available here, at that time.

While American nurseries and garden centers offer far, far more variety than was the case in the 1960s, much remains “collector” material, and languishes for want of knowledgeable customers. The plant-buying public seems dedicated to purchasing the limited, box-store selection that frustrated Polly Hill. Too much Leyland cypress, too many Norway and red-leaf Japanese maples, too many top-worked weeping cherries!

There is such a thing as a worthwhile tree. The pre-eminent voice for making distinguished tree choices, every time you plant one, is Michael Dirr. Dirr is the author of the tree lovers’ bible in its many editions, “Manual of Woody Plant Material,” in addition to a dozen other books. A perennial subject of Dr. Dirr’s talks is his advocacy for noble trees.

What are noble trees?

While known for his introductions of crape myrtles and hydrangeas, Dirr is particularly passionate about trees, and he advocates planting large shade trees, or noble trees, which he describes as “anything that spans generations, has a long life, supports wildlife, fixes CO2, spits out oxygen, prevents erosion, and increases property values. We need large trees.” Click on for a .pdf of Dirr’s assessments of noble and “noblette” (smaller scale) trees. If you read the assessments, you can understand the importance of nomenclature and cultivar information that I include in Garden Notes: Why end up with a wrong or poor choice?

I am more of a nerd in this respect than most regular people; however, Dirr has done all of us a service with this campaign and his continual evaluations of species, new introductions, and cultivars from both sides of the Atlantic and from around the world.

We added two trees to our home landscape in November, both acquired from Polly Hill Arboretum: a choice katsura, Cercidiphyllum japonicum ‘Rotfuchs,’ and, from the horse chestnut family, a North American native yellow buckeye, Aesculus flava. Won’t you add a worthwhile tree to yours in 2018?