Written by davethetreecenters • February 07 The Yin and Yang of Viburnums

Some plants are so packed with charisma that they can become cult items, admired and coveted by every gardener who encounters them. To achieve this status usually requires two things – at least one unique feature of outstanding beauty and being not too easy to grow. That way, when you succeed with it, you get to enjoy the beauty, but also bask in the glory of your achievement – even if it is only a postcode lottery of where you happen to live. Of course, let’s not be too mean, because what makes a great gardener is knowing what plants will succeed in a particular garden, with its climate, soil, light and other unique characteristics – and then planting them. Now we have a way to overcome these problems and get a coveted look without a massive amount of effort. So bear with me while I explain, and reveal the Yin and Yang of the world of Viburnums.

David’s Viburnum

All those coveted features can certainly be found in David’s Viburnum, a gorgeous Chinese plant (extra points for being Chinese. . .) that features some of the most graceful and attractive evergreen foliage of any shrub, and that has one of the plant kingdom’s rarer features – berries in late summer and fall that are bright turquoise blue. It also helps Viburnum davidii that this plant was discovered early in the 20th century by one of the most famous of all plant collectors, Ernest Wilson, who brought back many new discoveries from China, for both British nurseries and Boston’s Arnold Arboretum. Plus, he named it after Armand David, an almost equally famous naturalist, who found many species new to Europeans while working as a missionary in China. All in all, a pedigree more ‘common’ plants can only envy – kind of the ‘Upstairs, Downstairs’ of gardens.

David’s viburnum scores well on the ‘not easy to grow’ scale too. It only succeeds to perfection in climates with mild winters (zone 8 is good) but with cool, moist summers – common in much of Europe, but rare in North America outside of the northwest. The soil needs to be rich and acidic, and it needs light shade – not too much light and not too little – to become the 4 foot wide and 3 feet tall shrub it can become. Finally, you need two genetically-different plants to cross-pollinate each other, and produce the spectacular blue berries, and that means growing several plants together.

Notice that these plants are not like holly bushes, where there are separate male and female trees, with only female trees having berries. You need a male tree, though, to pollinate the female. Viburnums are more like apple trees, where every tree produces apples, but you need two different varieties so they can cross-pollinate each other. This is true of all viburnums, so it always pays to have different varieties of the same species in your garden – that will give you lots of berries.

Wow, what a challenge! But before you move on to easier goals, let me reveal exactly what this blog is all about.

Creating the Yin and Yang Viburnums

Dr. Thomas Ranney has pretty much the ideal life. He works at the Mountain Horticultural Crops Research and Extension Center of North Carolina State University. Sitting in the hills, surrounded by state forests, he gets to run the Crop Improvement Lab, where he can concentrate on his passion – breeding plants. Winner of multiple awards, and responsible for many great garden plants, he too admired David’s Viburnum, and knew how hard it was to grow well. So he had an idea.

It is well-known that hybrid plants – made by cross-pollinating two related species together – are often more vigorous and tough than either parent. Breeders call this ‘hybrid vigor’. The plants need to be closely related to be able to make successful crosses, so of course you can’t cross an oak with a potato, or a rose with a banana! ‘Close’ almost always has to be the same genus (the first name in the botanical name), and usually they need to be ‘close’ within that genus too. First of, Dr. Ranney looked around for Viburnums that are close to David’s Viburnum. They would probably need to be from China, so he looked there.

It turned out that Ernest Wilson had also introduced the plant that was to be the answer. Wilson brought it back to America in 1901, but it had never become popular, and was really only found in specialized collections and botanical gardens. Usually called the Chinese evergreen viburnum, Viburnum propinquum looked pretty similar to David’s Viburnum. It has leathery oval evergreen leaves and a nice compact form, but the berries were a more common navy blue to black, not the turquoise that made David’s Viburnum so desirable. Most importantly, it is happy to grow in the southeast, and doesn’t mind heat and humidity too much – unlike, as we have pointed out already, that fussy David’s viburnum.

Early this century Dr. Ranney got to work. He crossed together Viburnum davidii and Viburnum propinquum, taking pollen from one plant and fertilizing the other. He ended up with a batch of seeds that did germinate and grow, producing a mixed bag of seedlings. Once those flowered he crossed together the most promising ones, and in 2011 picked out a plant that looked an awful lot like David’s Viburnum, with turquoise berries, but was perfectly happy growing at the Crop Center, in hot and humid North Carolina. He named it officially as ‘NCVX2’. A few moments of thought will tell you what the letters stand for (hint: the symbol ‘x’ is used to indicate a hybrid plant*). He then tested his other seedlings in pairs with ‘NCVX2’, to find out which ones gave the best cross-pollination, When he found the best on for mutual cross-pollination, he called it ‘NCVX3’. Both of these plants were patented, to protect his hard work, and fund more research.

Meet The Yin and Yang Viburnums

Now of course those are boring names no one will remember, so Dr. Ranney needed something much more catchy. Something Chinese-themed perhaps . . . . yes, of course. Since they went together, they were the Yin and Yang of Viburnums. ‘Ying’ is the female principle, and ‘Yang’ the male, among the many other things attributed to these complementary forces, the primary and first split of the unified force – Taiji – that is the whole universe.

The Yin Viburnum  (‘NCVX2’) and the  Yang Viburnum (‘NCVX3’), are bushes that looks very similar to David’s viburnum, with the same leathery, evergreen leaves with three pronounced veins running along their length. Fertilized by each other, they will produce the great crop of blue berries you see at the top of the blog. Very similar to the parent, but the berry stalks are not as red as we find in David’s Viburnum. They are great evergreens for semi-shade in neutral to acidic soils, growing in time to be around 4 feet across and 2 feet wide. Simply mix them together in roughly equal numbers, and create a wonderful bed. Wonderful in spring, with an attractive show of fluffy white flowers. Then the excitement of waiting for the clusters of green berries to turn blue, and when they do, a fabulous display for late summer and fall. All year round some of the most attractive evergreen foliage of any shrub. To top it all off, way easier to grow in the southeast, with much better resistance to heat and humidity in summer.

It’s time to get planting, don’t you think?