Does the shorter growing season in Maine impact the height of plants like American Holly?
I am looking into putting American Holly in my yard, specifically Blue Princess and Prince. I’ve read online that it can grow 10 feet tall but other local sources say 4-6 feet tall. Do plants in Maine not grow as tall as they say online because the growing season here is shorter?
While the short Maine growing season can absolutely impact the height and general growth pattern of annuals, a long-lived perennial’s mature height is less affected by the season’s length than it is by general growing conditions (light, soil, water). For your question, I consulted one of my favorite reference books, the “Manual of Woody Plants,” by Michael Dirr (this book is probably on the desk of every horticulturist at every Extension across the country…). I have good news, bad news, and more good news.
First, ‘Blue Princess’ and ‘Prince’ (both cultivars of Ilex x meserveae) are terrific cultivars that should thrive in your yard. The evidence presented in Dirr did mention they can sustain some winter kill of foliage in very cold winters, and that plantings with north, northeast, and northwest exposure did better. Regardless, they might need a bit of protection on the coldest nights, but should otherwise do fine. The bad news for your question is that every source I’ve checked puts the mature height in the 10-15′ range, which they might not reach *quickly* because of our short growing season, but would probably reach *eventually.*
Which brings us around to the second good news–these plants are easily pruned and if you’ve fallen in love with the cultivar, it can be maintained at the height you’re looking for, but it will take some attention now and then to preserve them once they attain the size and shape you’re looking for. And pruning them in the winter can give you nice holiday decorations, to boot. If you aren’t looking for something that needs the extra effort, a different plant may be in order, but this is absolutely a garden to-do item that the average gardener can easily handle.