There are main beliefs behind flourishing implementation in every art form and merging plants into gorgeous arrangements is every bit as much an art as is music or painting. Complete books are devoted to the subject matter of merging plants, but a few universal principles can here be outlined which might prove helpful.
Eclecticism is the most general indulgence of beginners, with one of these and one of those… Whereas this can make an inspiring collection of botanical specimens, it will not make a very acceptable garden.
Some of the most fine-looking scenes in nature consist of a massing of a major plant steadily giving way to another largest plant in a natural drift, with an area in which both amalgamate. If these plants correspond and or distinguish adequately, the result is particularly outstanding. Often this will be with a consistent backdrop and or forefront of some single or methodically intermixed planting of another type which ’sets off’ the major focal plantings.
So, defining the region, producing a constituent or unity with a meticulous look within the garden, which merge into another component in close harmony or distinctive contrast is one key to merging plants.
This look need not be shaped with only one kind of plant and are often all the more prosperous and fascinating if several plants having strong resemblance and some differences are intermixed. A combination I personally enjoy, for example, is flecked ornamental grasses mixed with Iris and variegated Iris, with drifts of variegated liriope and an occasional daylily. All these are blade-leaved plants and together create an idiosyncratic compositional ingredient while providing distinction in detail and in blossom.
Right in the center of this I may place a dappled Hosta, or run the blade-leaved planting into a planting of Hosta, and I may place a Hydrangea macrophylla mariesi to the stern of the planting. The variegations all harmonize, relating even the Hosta and Hydrangea to the blade-leaved plants, and the broad leaf of the Hosta and Hydrangea distinguish very well with the shrubbery of the others.
Which brings us to the fundamental principle: Relationship? What was just explained is a planting in which all the plants concerned relate to each other through several of their distinctiveness. If you take any two vegetation you have, or pictures of them, and put them jointly you can begin to see what is meant by relationship. Do they do anything collectively? Do they intermingle, visually? Does each underline the qualities of the other or does nothing happen - there is no association that you can see?
This is analogous in principle to merging colors efficiently except that with plants it is more multifaceted because we are working with the general form, with the consistency created by the plants, with the individual leaves, with leaf color and with flower form and color. But the thought is the same. Is there an association? Do the plants work collectively? If not, then don’t put them mutually.