A combination of modern horticultural apathy and too many choices was probably the demise of conformity in home gardens. Formal hedges or even informal screens of several of the same plants are nearly obsolete. Ironically, long and low barrier hedges and so called ‘orchards’ of identical trees planted in regimented rows or grid patterns have become common in large landscapes in public spaces.
Those of us who still crave formal hedges, paired trees or any such symmetry in our home gardens must be more careful with the selection of the plants that need to conform than would have been necessary decades ago when there was less variety to complicate things. It is just too easy to get different varieties of the same plant. Only plants with matching cultivar (cultivated variety) names will necessarily match. (Yet, on rare occasion, even these are inaccurate.) For example, ‘Emerald’ arborvitaes will match other ‘Emerald’ arborvitaes, but will not match ‘Green splendor’ arborvitae, no matter how they resemble each other in the nursery.
Plants that are identified by their characteristics instead of by cultivar name are riskier. Blue lily-of-the-Nile could be any one of many different cultivars with blue flowers. It is therefore best to obtain all lily-of-the-Nile for any matching group from the same group in the same nursery at the same time. What will be available next week may actually be a different variety with a different shade of blue and different foliar characteristics. Nurseries bring stock in from so many different growers.
Adding new plants to replace those that have died within established hedges or streets flanked with the same trees can be particularly difficult, especially if the old varieties are no longer available. The old fashioned yellowish Japanese boxwood that was so common for small hedges in the 1950’s has not been common in nurseries for several decades. Replacement plants are darker green. Some are even compact cultivars or different specie like English boxwood. When lined up and shorn together, they make ‘calico’ hedges.