Are you a Good Sport or a Bad Sport?

This week, we spotted a variegated sport on a large hedge of Thuja ‘Green Giant’ at JLBG. Sports are a common term used to refer to plant mutations. These mutations, which are often chimeral in nature, occur due to an error during the cell division process. This is similar to what happens when cancers develop in animals. Some sports have great ornamental value, while others may have undesirable traits.

As a plantsman, we always enjoy finding new sports, but we do so, knowing that most have no real value. Many times each year, we are contacted by gardeners who have also found sports, most of which mistakenly assume the sports have significant horticultural value. The reality is that probably 99% of all plant sports are neither desirable or valuable. So, let’s analytically evaluate our new sport below.

Thuja ‘Green Giant’ sport

Green flag #1 is that it’s a sport from a well-known parent, Thuja ‘Green Giant’. The next thing to assess is whether or not the plant can be propagated and retain the qualities of the sport. In this case, the answer is yes, so that’s 2 green flags. The third thing to determine is the stability of the sport. With many sports, the stability of this irregular variegation patterning is concerning. While this pattern is not stable in some plant groups, it does tend to stay irregularly stable in conifers, so that’s green flag #3.

The next thing to evaluate is how the variegation will affect the growth rate of the plant once it’s on its own roots, and not attached to an energy supplying parent. As the chlorophyll (green) pigment is replaced by carotinoid (yellow) pigment, growth usually slows. In this case, small sectors of green growth seem to constantly re-emerge from the gold sectors, which will reduce the vigor, but not to the point at which the plant never grows larger. It will absolutely keep it out of all commercial markets except for small, boutique specialty growers, who propagate their own plants. This would be our first yellow caution flag.

The first red flag is the foliar burning that shows up as a browning of the yellow tissue. Sometimes, this is a winter only problem, due to chromoplasticity, but usually not. If the yellow growth burns while it’s attached to the parent, it will most likely burn worse, when rooted and growing on its own. Some of the burning can be mitigated by providing some light overstory shade, but that will also slow down the plant growth rate and make the plant more spindly. So, our evaluation of this sport concludes with 3 green flags, 1 yellow flag, and 1 red flag. In this case the red flag (foliar burning) overrides all of the positives, so, sadly, this will probably never be anything more than a short term novelty.