Sunday, May 4

Avoiding the rhododendron police

Ironclad varieties for northern gardens

Given a modicum of care, rhododendrons can add classic elegance to any garden.

Why are evergreen rhododendrons often excluded from a retail nursery's replacement warranty? Do nursery professionals have something against these plants? Or against the average home gardener? Not at all! Factors outside the nursery's control - and most often within the gardener's - are responsible for what some perceive as a harsh way of doing business.

I could say, "Don't take it personally," but the truth is, I want gardeners to "take it personally." That's because you must be ready to accommodate the reasonable needs of these plants if you expect to have success with them. Think of bringing them into the family the same way you would think of bringing home a new baby or acquiring a new pet and you'll do fine. Not every gardening success is meant to be achieved blindfolded and with your hands tied behind your back!

The key to success

'Nova Zembla' is an old garden hybrid that has proven its value over time. Photo by Bob Gabella

The deep red blooms of 'Joshua' grace Gene Paschall's Palos Heights garden. Photo by Kim Carpenter

The first thing to consider with evergreen rhododendrons is variety. They are divided into two main groups. The large-leafed, known properly as elepidotes, are exemplified by the familiar red cultivar 'Nova Zembla.' The lepidotes, or small-leafed varieties, are probably best represented by the ubiquitous 'PJM.'

The next thing a gardener must consider is proper siting. If you don't have conditions suitable for these plants, consider building microclimates to accommodate them. Well-placed buffers of larger deciduous shrubs, small ornamental trees or smaller specimen evergreens provide visual anchors and moderate the strong summer sun and sweeping winter winds that dry them out.

Growing conditions
The lepidotes are the easiest variety to grow and the earliest to bloom. Since the familiar purple of 'PJM' could become tiresome, 'Aglo' in medium pink, 'Mary Fleming' in a pastel yellow and pink blend, or even 'Tow Head' in pale yellow, can offer relief. (None are as easy to find as 'PJM,' so refer to our source list.) All combine wonderfully with spring bulbs and early perennials. They are, as rhododendrons go, fairly tough. I even have two groups of 'PJM Elite' on the west side of my home--one closer to the foundation and one well out in the open. Both plantings are on level ground, as I would never consider planting them on a slope. In both cases I amended the entire bed, not just the individual holes, with a 25-percent backfill of organic compost dug in about a foot deep. As with my deciduous azaleas, I also add granulated soil sulfur at four pounds per 100 square feet. The ideal pH is 5.5-6.5 and good drainage is essential. These smaller varieties go in on two foot centers, planted at the same depth as in the pot, but larger elepidotes may need up to four feet or more between plants. The entire planting is dressed with a few inches of loose organic mulch. Feeding with a light manure tea, half strength fish emulsion, Holly Tone, or other acid-loving plant food is best once in spring before buds show color and again after the new growth begins. I do not fertilize them later than June - with the possible exception of a sick or ailing specimen. (Believe me, you will occasionally play doctor with these plants!)

'Purpureum elegans' is another favorite for Northern Illinois gardens. Photo by Bob Gabella

Fortunately, evergreen rhododendrons are not tasty to most rodents or deer. The most troublesome pest is the black vine weevil. Its larvae destroy the root system and as adults it cuts notches in the sides of the foliage. The best control is a springtime drench of beneficial nematodes such as Steinernema feltiae, available from a wide range of sources. Periodical cicada did heavy damage to my plantings last summer, but all have recovered. The most troublesome pathogen is Phytopthera stem canker. A severe infection can cause entire branches to die. The best way to avoid Phytopthera is to grow the plants as stress-free as possible.

Elepidote rhododendrons such as 'Nova Zembla' and 'Purpureum elegans' can be equally successful here. The newer hybrids like the orange-red 'Helsinki University' from Peter Tigerstedt of Finland, 'Azurro' from Hans Hachmann of Germany and even the beautiful yellow 'Hong Kong' and pastel pink 'Janet Leach,' hybridized by the late David Leach of Ohio, are expanding both the hardiness and color palette of these plants. All appreciate a bit more afternoon shade than the lepidotes, and all, when well grown, are spectacular.

Why not rise to the challenge and adopt a few of these evergreen rhodies? Consider them your children; dote over them a bit. But as they settle in and grow, stand back and watch. They will make you proud. And, as in any long-term relationship, you may have a few bumps along the way, but I assure you, the rewards will be worth it!

For information on where to purchase unique rhododendrons and a list of varieties recommended for our area by the American Rhododendron Society, click here.

A lifelong gardener, Robert F. Gabella has been involved in the horticulture industry since 1983. With an AAS in ornamental horticulture and a BA in business management, Bob is an Illinois Certified Nursery Professional, an independent consultant, hybridist, writer and photographer. He also tends prize-winning gardens at his Villa Park home.