Answer: In my experience, there are many variables -- both pragmatic and esthetic -- that go into the selection of a particular cultivar in a landscape plan. For this reason I would suggest you contact the original landscape architect or designer who specified this plant and ask them what they would like to see substituted. Alternatively, you could ask your supplier what they have available and make a selection from that listing.
Unfortunately, without knowing why the original selection was designated it is very difficult to suggest something else. For example was it based on height, width, winter foliage color, bloom color, bloom sequence, is it something that is just usually easy to find locally or was there simply a nice batch available at the time the plan was drawn, or what?
If on the other hand there is some underlying compelling reason for that particular variety (for example there is a special significance to the name), it might be worth ordering it specially, even if it means waiting until next spring.
GOod luck with your installation.
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