JARS v38n4 - The Rest of the Year
The Rest of the Year
Parker Smith, Sebastopol, CA
Most rhododendrons bloom in our gardens two to three weeks out of the year. Looked at another way, rhododendrons are without flowers for 95% of the year. Excellent foliage is an attribute of most rhododendrons and by taking advantage of this and other non-flowering features that many offer, we can create combinations that provide visual excitement and interest in the garden long after the flowers have passed. Most of today's gardens are quite limited in area, making it all the more critical to create plant combinations that compliment the spaces they occupy throughout the year.
Ideally we should determine the effects we want to create in our garden, choose plants with the characteristics that accomplish the desired results, and then install the plants that achieve our goals. More commonly, we collect rhododendrons for their individual virtues, primarily their flowers, then attempt to combine these into a pleasing garden arrangement. Either way can be successful if we take the time to observe the similarities, differences and individual characteristics of the rhododendrons that we combine.
Whenever we combine plants we are practicing 'planting design' whether it be on paper or outside in the garden. Many factors require consideration when making these decisions. The basics of plant size and form, overall color, and textural effects, plus the flower color and season of bloom all require evaluation and determination at the outset. There may be cultural and environmental factors that will affect the plants appearance that should also be understood at this stage.
If your garden is spacious and your primary use of rhododendrons is for mass foliage and seasonal flower color effect viewed from a distance, then application of the basic design considerations should be adequate. When rhododendrons are going to be observed at closer range, as we are virtually forced to do in a typically sized garden, then additional factors come into play. Close observation of any plant means the foliage, and often individual leaves, take on greater importance than the overall effects of plant form, color, and texture. These 'leaf characteristics' can aid in combining rhododendrons into flowing, well integrated plantings that are interesting throughout the non-blooming seasons.
The character of a leaf is composed of its size, shape, color, surfaces, edges, density of foliage and the manner of attachment to the branch. Unless there is a relationship in most of these characteristics between the rhododendrons in a group, the element of continuity will be lost and all that will be created is a busy, unrelated mass of plants. Successful plantings can be created by combining plants having a majority of similar leaf characteristics while contrasting one or two others to provide interest. Major accents can be created by installing a plant having similar leaf characteristics but being very different in one or more of these or in an overall plant effect (form, color or texture).
Even though rhododendrons comprise a single plant genus, there is tremendous variation in their foliage characteristics. Leaf size differences are great from the huge R. sinogrande leaves to the tiny ones of several azalea species and hybrids. The plants textural effect is the result of the leaf size, shape, quantity of foliage and the nature of the spaces between the leaves. Major changes in leaf sizes in a plant grouping need to be carefully blended with intermediate sized except when a significant accent effect is desired.
Leaf shapes exhibit as tremendous a variation as sizes do within this genus. The rounded leaves of R. williamsianum and the narrow foliage of R. strigillosum and their hybrids, form the extremes with the great majority of rhododendrons somewhere in between. Generally a similarity in the leaf shapes is necessary if a feeling of continuity is to be attained within a plant group. This does not mean each plant in the group must have the same exact leaf shape, but rather their foliages should provide a similar feeling. For example, R. 'Crest' and others with a rounded end to their foliage combine well with R. williamsianum hybrids having quite round leaves. There are also leaf shapes which fail to fit strongly into any particular category and these can be used to form transitions between groups having more distinct leaf shapes.
'Parlevou' leaves spaced along stem not in typical whorls
Photo by Parker Smith
The close-up leaf color and the overall plant color is usually very similar in rhododendrons. This is due to the leaf usually being a solid color, with little or no variation from the center to the edge. Major color changes should be blended by using intermediates, much the same as with textural changes. When color contrast is desired, it is safer to simply insert a plant having much lighter or darker foliage but of the same general color (i.e. yellow green, blue green, etc.) as the rest of the group. Color combinations, more than any other design consideration, are personal choices as to what colors you prefer to see together.
deeply veined leaf surface
Photo by Paul Molinari
Upper surface leaf characteristics (dull, glossy, smooth, deep veined, etc.) can be combined to strengthen the continuity of a planting or provide contrasting interest within the group. A glossy foliaged individual among several dull leafed plants will accent it to a similar degree as a color or textural change. Smooth leaves can be contrasted with heavily veined ones ( R. smithii ). These characteristics can also be used in non-contrasting, blending ways by using intermediate forms to complete the transition from glossy to dull or smooth to deeply veined leaves.
The underside of the leaf can also be a strong element in plant combinations when easily observed, such as with the new, upright growth of some rhododendrons. Special color interest is the usual result provided by the indumentum or scales on the lower side of the leaf. Combining plants having this upright characteristic that exposes the underside of the new leaves provides an interesting effect, often with spectacular color interest.
twisted foliage character
Photo by Paul Molinari
Just as the shape, surface, and underside of a leaf can affect its character, so can the edge. It can be rolled (not just due to weather conditions) or wavy (R. 'Jan Dekens'), twisted ( R. laxiflorum ), plain (many hybrids), or hairy (R. 'Thalia'). Again, combining rhododendrons having similar leaf edge characteristics will create plantings that have a feeling of belonging together. Those who have resident root weevils could put the most susceptible rhododendrons in one grouping with the resulting notched leaf edges creating the plantings strongest element of continuity!
Overlapping leaves tightly held to stem
Photo by Parker Smith
The leaf's attachment to the branch has a major affect on the character of the foliage. Most rhododendrons have whorls of leaves radiating around the branch, but there are exceptions (R. 'Parlevou'). Some whorls of leaves are tightly held against the branch with little or no leaf stem and with a portion of their foliage overlapping ( R. haematodes and R. 'Buttermint'). Other rhododendrons have long leaf stems, separating the leaf from the branch and usually setting each leaf off as an individual with no overlap within the whorl (R. 'Loderi'). Some leaf stems arch while others remain quite straight. Others exhibit colorful leaf stems which can provide interest and accent when these plants are placed among a group with green stems. The angle at which the leaf stem comes off the branch, if extremely tight to the branch ( R. chapmanii ) or nearly perpendicular, can contribute to the leaf character. Some plants hold their leaves differently when growing in full sun than in partial shade (R. 'Noyo Chief').
'Noyo Chief' leaves held at
45° angle when grown in full sun
Photo by Paul Molinari
leaf angle very
tight to branch in full sun
Photo by Paul Molinari
A little close-up observation of your rhododendrons can go a long way toward successful garden arrangements. Assuming that all species in a particular series, or most hybrids having the same parent on one side, will look well together does not always hold true. Some species ( R. williamsianum , R. griersonianum , etc.) do influence the leaf characteristics in their first generation hybrids to a high degree while other species fail to have such dominating influences. Choose plants to combine based on their foliage characteristics, not on their species classification or hybrid parentage.
Successful rhododendron combinations can be achieved in any garden if the leaf characteristics of the plants are combined and blended to form related groupings. Interest and accent can be created within the various groupings by subtly or dramatically contrasting one or more leaf characteristics. Rhododendron gardens are spectacularly colorful with their spring flower displays but they should also be exciting foliage gardens the rest of the year.