A Species Enthusiast Speaks
Dennis MacMullan, Greenwich, Conn.
Extract from paper written for ARS New York Chapter
FIG. 22. R. fulvum, in new growth.
Photo by Cecil Smith
My garden is located approximately one mile from Long Island sound. I am sufficiently elevated to be able to see across the sound to the North Shore of Long Island. My garden is very small, but since there are hardly more than three square yards that are level, I can accommodate far more plants than could be grown in a more "normal" planting site. A built-in advantage to this site is that drainage is aided considerably - and as we all know, poor drainage is one of the surest assassins of Rhododendrons. In our hot summers, excess water around a plant is a certain invitation to that unwanted guest Phytophthora cinnamomi - "Root Rot". I hope none of you have ever had the displeasure of a visit by "old droopy" but if you have, you know his calling card - not just one dead plant, but often everything in the area.
Species offer the enthusiast one thing (at least) that most hybrids do not - wide variance in leaf form, etc. This is even more true in the Northeast where most of the Maddenii, Irroratum, and Neriiflorum Series hybrids are not hardy. Since we live with our plants 52 weeks a year (some of us do get two weeks off for good behavior) and our plants flower (?) for about two weeks, shouldn't we try some varieties that will bring us pleasure for the remaining period of the year? Enter species!
In a small way I have been trying to work with certain species which have something to offer in three areas: (1) Excellent leaf form, plant habit, and often presence of indumentum (2) Flower color (3) Leaf retention.
The following list is comprised of species that have been winter hardy for me (with a little effort) for at least 2 winters (and summers). In winter I use burlap wind-breaks and also recommend a covering with salt-hay (which I have not yet used, but intend to this year.) Mice often tunnel in salt-hay and may chomp on plant leaves as a salad course so you have to be alert. It should pay off, however.
FIG. 24. R. crinigerum, Rock 2, showing
Photo by Carl Phetteplace
I work almost exclusively with cutting-grown plants because I have found that when working with specific clones of species there is considerable variance when selfed. Often no seed at all develops. Also when working with these "borderline" plants you will have more going for you initially with a rooted plant in your effort to bring it through a few winters. When the plant has proven itself to your satisfaction, seedlings can be developed.
I will not touch on Series that are probably being grown by most of you - Lapponicum, Ponticum, Fortunei, etc. There are a number of species within these series that are not being widely grown and I will mention them. Perhaps some of you will try a few listed - they are all marvelous plants. I hope this will be of some help so that you will benefit from some of my painful experiences. I have lost many plants due to over-fertilization (don't do it!), borers and other hazards. I fully expect to lose more - but at least not for the same reasons. However each year a plant survives, its chances of surviving for another year are greatly increased - older plants can survive increased adversity. Thus, those of you involved in hybridizing programs may really have something to work with if you can develop some of these species into sturdy plants. The rewards are far greater than the effort involved. That is the only thing I will guarantee.
There are other plants that I am trying (and intend to try) but they have not yet passed the test of "2 winters". Obviously there are many deciduous azalea species that should be developed such as the very prostrate R. nakaharae, R. amagianum, R. sanctum, R. wadanum, R. quinquefolium (a marvelous plant), R. serpyllifolium, etc.
Plant Series Winter Plant Damage
(s) = Winter Protection
Summer Protection Comments: R. argyrophyllum
also ssp. nankingense 'Chinese Silver' A.M.
Arboreum None (s) Semi-Shade Bright shiny foliage with plastered white indumentum below leaves. 'Chinese Silver' has truss with up to sixteen flowers. Highly recommended. R. crinigerum
also Rock #2 & Rock #38
Barbatum None (s) Semi-Shade
Typical Barbatum foliage with fine character. Bristle-coated leaf stems on all forms, even greater on Rock #38. Have seen this plant rated as H-2 and H-4 (Leach and ARS Handbook). Definitely worth a try. R. campanulatum
'Knaphill' - A. M.
Campanulatum Slight (s) Semi-Shade Excellent foliage and flower. RHS gave 'Knaphill' an extra star (4*) in its ratings. R. campylogynum
Campylogynum Slight Sun Excellent Rock Garden plant. Plum-purple flowers in bell form. Var. cremastum more upright. Var. 'Patricia' developed by Jim Caperci is actually a hybrid, but very similar to the other forms. R. rex Falconeri None (s) Shade "Yes, Virginia, there is a Santa Claus." This is the largest leaf plant that I am aware of that will grow in our climate. Leaves long and broad with beautiful new indumented growth. Develops into glossy upper leaf with fawn heavy indumentum below. Worth a try in a protected spot. If it never flowered it's worth having. R. fictolacteum Falconeri None (s) Shade Similar to R. rex with more indumentum on upper leaf surface. Leaves on my plant not as large. Plant also not as vigorous. Still very attractive. R. chlorops
Fortunei None (s) Semi-Shade Does very well for me. Beautiful blue-green foliage. Could be used in hybridizing for a yellow in our area. Highly recommended. R. imperator
(Carl English form)
Uniflorum None (s) Sun or
Good rock plant - this form larger in both leaf and flower than standard. R. campylocarpum
Thomsonii Moderate (s) Semi-Shade Semi-dwarf, excellent yellow. Fine leaf form. My plant has had winter damage but keeps coming back. R. campylocarpum
Thomsonii None (s) Semi-Shade Here is where varieties of the same plant will differ. Var. elatum more upright grower with paler yellow flowers. Planted within three feet of 'Hooker's form' it thrives nicely. R. souliei Thomsonii None (s) Semi-Shade This is a personal favorite - lovely leaf shape. The leaves of my plant are larger than R. wardii. Excellent pink flower. White form is available. A clone developed by Cox (Scotland) should be even hardier. Recommended. R. wardii Thomsonii Moderate (s) Semi-Shade Good yellow - saucer shaped flowers. Has been damaged each year for three con- secutive years. Needs considerable pro- tection. Suggest that specific clones be searched for to develop fully in our climate. R. pumilum Uniflorum Slight Sun or Semi-Shade Large flowers on tiny plant. Good rock garden variety. R. aureum (was R. chrysanthum) Ponticum None Semi-Shade The only Ponticum I will mention. Also an interesting plant to try from different seed. A nice, very dwarf yellow. Likes moist soil, good drainage. I have two forms, both from seed. Flowers when about three years old. Definitely recommended. Wada's form has more pointed leaves. Dr. Rokujo form rounded.