Bloomin’ rhodies keep at it on Martha’s Vineyard

Tree-like Rhododendron maximum extends the bloom season of the rhododendron family well into summer. — Photo by Susan Safford

Have actually spent much of my weekend working in the garden, instead of writing about Working in the Garden. The many seed capsules on the platycodon are snipped and the spent daylily flowers disposed of. The tomatoes are pruned. The cole crops are Bt’ed. The Dark Red Norland potatoes are dug — nice harvest. More cucumbers and their support are planted. The Fordhook Giant Swiss chard is dead-leafed. The seed-bearing stems of the lovely, invasive, violet adenophera are yanked. The hens greedily and gleefully eat the white grubs my grandson finds.

I leave leeks to flower and set seed when possible, as I have always found the flowers to be a magnet for pollinators of all sorts. This year I am observing far fewer pollinators than expected.

July has been beautiful but heat and humidity are up, way up. Heat stress may cause wilting, or flagging: plants appear to be dry when they are flagging but may be hot instead. Beware of over-watering and the ensuing rots and mildew. Frequent application of organic fungicide and compost tea may help to control foliar diseases during these conditions. Sanitation, keeping the soil around crowns and under plants tidied up and spent blooms deadheaded and picked up, should help.

Pretty good populations of Asian, Japanese, and oriental beetles are at work ruining floral perfection and chewing holes in vegetable and herb foliage. The first and last of these are easier caught at night with a headlamp or flashlight. Japanese beetles must go into the soil at night, for I usually see these during daylight only.

Sometimes it seems that a garden of once-blooming roses is what I should concentrate on. Maybe it would be better than fighting beetles. Their bloom would occur prior to the great onslaught of these flower violators, and that would be that. With roses that do a good job of re-blooming, we are just providing beetles with lunch, or applying obnoxious systemic poisons to the soil to try to “get control.”

Shady garden: Rhododendron maximum

Rhododendrons form a plant family that has exploded with variety supplied by newly introduced Asian species and hybrids of all sorts. According to Wikipedia, 28,000 cultivars have been entered into the International Rhododendron Registry. We have so much variety available now that it may be hard to recall that not very long ago there was far less choice in nursery stock, not only here on Martha’s Vineyard but also throughout the U.S. One of Polly Hill’s objectives in her extensive horticultural undertakings was to see what would do well on Martha’s Vineyard, to relieve the local plant monotony.

When I was growing up here, the Island rhododendrons were a far more subdued lot than today’s colorful hybrids. The famous Middle Road planting was there, along with those at the Welch camp on Lambert’s Cove Road and the corner of Franklin and Tashmoo in Vineyard Haven; and there were undoubtedly others I never knew about. Much of the rhododendron selection here derived from Catawbas and Rhododendron maximum, native North American species.

Now that we have had the benefit (or is it surfeit?) of a quarter-century’s hybridizing activity, perhaps it is time to take another look at good old R. maximum. It is sometimes called the great, the late, or the summer rhododendron, and it is, in fact, blooming now. It is also known as the rosebay rhododendron.

R. maximum is a quiet sort, with small pinkish or white blossoms, and lacks the large, showy flower trusses of its hybrid cousins; if you drove past the three blooming plants at my place you might not even notice them. It is probably the cold-hardiest native rhododendron and is classed in the “bigleaf” group. R. maximum’s evergreen leaves are long and strap-like, eight to twelve inches typically, creating good screening.

This rhododendron is capable of becoming large and tree-like over time. In its native range it forms an evergreen understory in mesic forests, with a range extending from Nova Scotia deep into Appalachia. In the Great Smokies these rhododendrons form their own habitat, where many rare wildflowers are found.

Michael Dirr, in “Manual of Woody Landscape Plants,” suggests it is not ideally suited to “normal” landscape situations, as it requires a cool, moist, well-drained root run, and for this reason perhaps is not often seen in the trade. William Cullina writes, in “Native Trees, Shrubs, and Vines,” that it can bloom in heavier shade than almost any other Rhododendron species. It layers easily; that it how I propagated my plants.

More for shade gardens

A knowledgeable friend has urged my exposure to much unfamiliar plant material, including two little-known members of the Hydrangea family, Deinanthe and Decumeria. You too may not know them, but if you garden in shade — and in this heat wave we are all more interested in shade — they are two to meet.

The American Horticultural Society’s “Encyclopedia of Perennials” describes deinanthe as a choice relative of hydrangeas, easily grown in cool borders, with appealing bluish-to-white flowers held above bold foliage. The plant I purchased is Deinanthe bifida, although there is another species, D. caerulea.

Deinanthe is hardy and easily grown in woodland gardens, becoming about two by two feet, where it can find cool, moist, humus-y soil. Its rhizomatous roots prefer well-drained conditions and the large-leaved shoots prefer some shelter from damaging winds.

The genus Decumaria, or “woodvamp,” contains two species, native D. barbara, and Asian D. sinensis, both vining plants. A woodlander, decumaria attaches itself to tree trunks by means of aerial rootlets and may grow from 10 to 30 feet up them. Foliage is mostly deciduous — deep green, oval leaves with pronounced points — that clothes what it grows upon handsomely.