Rhododendrons and Azaleas for the Chicago Area
Eldred E. Green, Chicago, Ill.
For some time precise knowledge of some of the kinds of rhododendrons and azaleas that can be grown in the Chicago region has been wanting. Unfortunately there have been no extensive collections that could be used as a basis for evaluating the many kinds. However, as a result of work that has been done during the past few years there are some points that can be made now with some certainty.
So far as the blooming season is concerned a proper selection of varieties will span a ten-week period. This is from the first week in May to the tenth of July.
Starting the season about the first of May are some showy azaleas. Two species from Korea, R. poukhanense and R. mucronulatum are earliest. The first is a prolific azalea species with large purple-violet flowers, and leaves that remain on most of the year so that it is almost an evergreen. The plant is rather spreading, and a dependable bloomer. The other is an upright grower, evergreen, and is classed as a Rhododendron. Flowers are numerous, about an inch across and a lilac color. There is a pink variety on the market and a hybrid, 'Pioneer," which differ but little from the species except in being a pink color.
Coming right along with these is the native species, R. canadense , which is commonly called the Rhodora. The Rhodora ranges through the New England and northern areas of the United States. It is a short, erect-growing shrub. Leaves are a gray-green color that is decidedly attractive among other foliage. The flowers are rather small about the size of a wasp, in large clusters and a bright purple. There is a pure white form. It is a little difficult to understand why the poet Emerson immortalized this tiny flower in verse unless it was the first sign of spring. However he did compare it to the rose, "Why thou wert there, O rival of the rose!" and provided the well-known couplet, "Tell them, dear, that if eyes were made for seeing, Then Beauty is its own excuse for being."
About the middle of May the evergreen rhododendrons start their season. One of the first is the hybrid 'Conewago' which is a hybrid between R. mucronulatum and R. carolinianum . The flowers could be described as a pale form of R. carolinianum on a more erect, smaller-leaved shrub. They are in clusters and make a good show during the first week in May until the end of the month. Coming along with them are the flowers of R. carolinianum itself. This is a low-growing evergreen Rhododendron from the Eastern mountains. Flowers are about an inch across in clusters. The species is a light pink. A white form, R. carolinianum album , is pure white, more compact in growth and makes a better display due to the sharper color.
The earliest of the really large flowered Rhododendrons is 'Boule de Neige', a low growing pure white variety. This is a striking plant for foreground use. Growth is compact. The flowers do not have any yellow in the throat.
Flowering with 'Boule de Neige' is Gable's hybrid azalea 'Stewartsonianum' which is evergreen and a fire engine red. This variety needs more protection than some. A good mulch will help prevent bud blast. About the middle of May the early varieties of Ghent azaleas such as the double 'Narcissiflora' start. Along with them are the early Mollis hybrids like 'C. B. Van Nes' and 'J. C. VanTol'. Other varieties follow rapidly. The native Pinkshell azalea, R. vaseyi , with its flowers of a soft apple blossom color blooms at this time. This is considered to be the best of our native azaleas.
Toward the end of May the profusion of bloom really starts. Rhododendron smirnowii , a reddish colored, wooly-leaved species from the Caucasus Mountains is a day or so ahead of the rush. Some of the varieties that bloom now are Rhododendron 'Album Elegans', 'Boursault', 'Butler's Port', 'Caractacus', 'Caroline', 'Catawba Grandiflora', 'Dr. Dresselhuys', 'Roseum Superbum' and a slightly pinker form called 'English Roseum', 'Roseum Elegans', and 'Mrs. C. S. Sargent' to name some of the more common varieties. 'Catawbiense Album' is a little later, a day or two.
In the azalea group the end of May (about the 22) is the high time. The large number of Ghent hybrids come in bloom, including the red-orange 'Coccinea Speciosa' and the very similar 'Gloria Mundi', 'Daviesi' with white flowers and 'Fanny' with pink ones come in now. The double Ghents 'Norma' and 'Freya' are in bloom at this period.
The Mollis azaleas like this time, too. 'Lemonora', 'Mrs. Peter Koster', 'Queen Emma', 'Hugo Hardizer', 'Golden Sunlight' are some of the showy ones. Also in bloom are the Knaphill and Exbury hybrids.
This list does not exhaust the possibilities as there are dozen of other varieties that flower during the latter part of May. Flowers on many of these plants last for many days and even weeks and the dates listed are for the opening time, the period when the plant could be said to be really in flower. Lower or shaded buds will open later so a long period of bloom occurs.
As the large mass of bloom passes the new foliage takes over and the entire plantings are a mass of new growth. But as July approaches the Rosebay of the southern states, R. maximum comes into flower. There are a few pink forms of this and they are useful to bring the season into July. At this same time the Swamp Honeysuckles, two tubular-flowered, fragrant species of azaleas from the south come into bloom. These are R. viscosum and R. arborescens . And so in the middle of July the rhododendrons and azaleas are over.
What about cultivating these plants? There are two major requirements, a humus-rich soil and winter shade. Both of these are easily supplied. In creating a humus-rich soil use plenty of sphagnum or imported peat moss or rotted oak leaves, pine needles, sawdust or wood chips. With sawdust or wood chips additional nitrogen may be necessary to prevent injuring the plant by nitrogen loss during decomposition. Peat moss of the sphagnum type has been found to be extremely beneficial as its composition has a chelating effect on minerals that are needed by the plant. Using plenty of the humus mentioned when planting will get the plants off to a good start. A good azalea or evergreen fertilizer mixed in this material is very desirable. Be sure drainage is good. One way is to add the humus on top of the present soil and mix it into the top few inches. This will raise the bed.
Winter shade is obtained by selecting planting sites that are on the north sides of building, in the shade of evergreens, underneath oak and other large trees. The most recent studies have shown that winter injury is caused or greatly increased, by winter sun heating the leaves to above freezing followed by below freezing temperatures occurring rapidly when the sun leaves. In the case of small plants protective screens can be used but the right planting situation is preferable.
Summer shade usually is automatically secured when winter shade is provided. Summer shade is desirable in raising the humidity and lessening the need to water.
Many of the so-called rock garden species have not been too successful in this region. This is not from any lack of hardiness: they survive our coldest winters but they usually fold up in summer, generally in late spring when the climate shifts from a moist, cool air to the hot blasts from the plains. The right situation that would avoid this problem seems necessary for success with species such as R. racemosum , R. impeditum , R. williamsianum , etc.
Feeding should take place either by a regular application of granular fertilizer once a year, or by liquid feeding not over twice a year, once when growth starts and again about a month later. Ortho and Plant Marvel are both products with formulas designed for these plants for liquid feeding. Watering should be done whenever the soil becomes slightly dry. This is important during the first two years when the roots are close to the surface. After that they can withstand considerable dry weather without damage as the buds for next year are formed about the end of July-before our heavy droughts usually occur.
A mulch, preferably of oak leaves (chopped are best), wood chips, sawdust or pine needles, helps keep the soil moist and adds to the appearance of the bed. These plants have shallow roots and should not be cultivated.
Other plants that grow under these same conditions are holly, Clethra, blueberries, ferns, wild flowers, and some of the early bulbs. Other shade desiring plants such as Violas, Bergenia, columbine, and the bleeding hearts are additional possibilities.
All considered, if you live in this area and have a shade problem in your garden try these unusual and lovely rhododendrons and azaleas. They are easily grown with the main consideration being to start them right as outlined above. Spring is the preferred planting time but plan now for the place where you will plant next spring. This fall will be a good time to get some oak leaves which many parks, homeowners and cemeteries are anxious to dispose of.