Boxwood bushes are garden standards – evergreen bushes with many uses, from the traditional boxwood hedge to less formal shrubs in modern gardens. Because they have such a well-known name, new gardeners can easily think they are all the same, and that one boxwood is just like any other, so why not just grab the cheapest thing at a big-box store?
In fact, boxwoods are a diverse group of plants, the result of coming from different parts of the world, and of centuries of selection and breeding by boxwood enthusiasts. So although they may superficially look similar, with their small, rounded, glossy leaves, especially when the plant is young, they can be very different. Some grow well in cold areas, while other don’t. Some thrive in the heat of the South, while others sulk and protest. Some grow round and fat, perfect for trimmed globes or low hedges, while others are tall and slender, making screens in narrow spaces, or striking accent specimens.
All this means that a little knowledge, and a clear idea of what you want, are needed when it comes to choosing boxwoods. That way, you will achieve the look you want, your plants will be happy, and your garden will be just what you dream of, without the frustration (and cost) of failure.
Boxwoods and Winter
The most common problem with boxwood bushes is browning of the foliage in winter. This might be mild, with just a few brown leaves at the top, or severe, with branches killed as well, and sometimes with the whole plant dying. One possible cause is dryness, and that can affect all boxwoods, so remember to water deeply two or three times towards the end of fall, so that your plants have plenty of moisture around their roots. Putting down mulch in fall, rather than spring, is valuable too, as it keeps the soil warmer, preventing or at least reducing freezing. Frozen soil is tough on your plants, so that mulch will help them. Make sure you don’t cover the branches or leaves with it, or the main stem, just the soil.
If you live in zones 4 or 5, winter injury is very likely, and you need to choose your varieties carefully. Boxwoods from Asia are more resistant to winter cold than those from Europe, (which include both the English boxwood and the American boxwood). Look for Korean boxwood, if you live in colder zones. This plant is confusingly called by two names. The correct one is Buxus sinica var. insularis, but it can also be called Buxus microphylla var. koreana by some gardeners. The variety ‘Wintergreen’ is certainly one of the best, with dense growth, and good foliage color.
There is also Japanese boxwood, correctly called Buxus microphylla var. japonica. This species is also more resistant to cold, and comes in a number of varieties, selected for shape and foliage. There is also Littleleaf Boxwood (Buxus microphylla), which if very similar to the Japanese kind. ‘Winter Gem’ and ‘Baby Gem’ are top choices among the cold-hardy Japanese boxwoods available. If you do want to use a European boxwood in zone 5, then choose the variety ‘Katerberg’, sold as North Star®. It is securely hardy in cold areas and it makes a perfect rounded mound of green.
As you can imagine, gardeners up in Canada are especially interested in cold-hardy boxwoods. Way back in the 1950’s Sheridan Nurseries, in Toronto, produced a batch of seedlings that were a cross between European and Korean boxwoods, a tricky thing to create. Asian boxwoods usually have paler leaves, and don’t grow as densely as European boxwoods, so improvement was needed. Among those seedlings were plants that survived the Canadian cold magnificently, and has rich green, dense leaves too. Some were fat and round, others were more upright. All these great plants for cold areas have ‘green’ starting their name. Look for ‘Green Mountain’, a taller plant great for cones and taller hedges, or ‘Green Gem’, a superb rounded ball of foliage, for low hedges and balls. ‘Green Velvet’ is another, with great foliage color.
Boxwoods and Heat
Japanese boxwood is also valuable in hotter zones, where the stress of heat, dryness and humidity takes its toll on European boxwood. One top pick is ‘Green Beauty’, which was another Sheridan plant, but one that turned out to be very heat resistant, and it stands out as the #1 choice for hot and humid states.
Boxwoods in Planters
Besides growing them as hedges and specimens in your garden, boxwoods are very popular for planters. They can be grown alone, to make elegant specimens, as balls, cones, or fancy spirals. You can mix them with other shrubs in informal planters, without clipping, or surround those clipped ones with cascading flowers in summer, and bulbs in spring.
One thing that is not very well-known, and causes problems, is the fact that roots of plants are almost always not as hardy as the top growth. After all, when air temperatures are below minus 30, the soil is probably above zero. But when we put plants into containers, and leave them outdoors all winter, the soil freezes almost as cold as the air – and this kills roots, causing your plants to die. So, if you want permanent plants in pots and planters, you should follow this simple rule – choose a plant that is two zones hardier than where you live. In other words, if you live in zone 6, you should plant in pots as if you lived in zone 4. In zone 7, make sure the variety you choose is reliably hardy in zone 5.
Those cold-hardy boxwoods for northern gardens turn out to be the best choices for pot-growing in warmer zones too. Choose wisely, select one of the varieties mentioned above, and your plants will come through the winter unharmed. You can see though, that if you live in zone 5, and certainly in zone 4, boxwoods in planters need special care. The easiest solution is to grow them in their own pot, ‘planted’ inside the box. That makes it easy to remove it in late fall, and plant that pot directly in the garden, protected by some mulch. Roots will have grown through the drainage holes of that inner pot, but don’t worry, just trim them off before planting in the garden.
Boxwoods of the Shape You Want
Finally, consider what shape you want your boxwood to be. Although you can clip to different shapes, it is much easier if the plant already grows the way you want. For balls, choose rounded varieties, and for cones, upright ones. Letting plants grow naturally is also a great thing to do with boxwood – they develop lots of interesting character as they get older. By choosing the right variety, you can get roughly the shape you want for the spot you want to fill.
Especially interesting are some super-narrow varieties, that will grow up to 10 feet tall, yet be just a foot or two across. These make great accent specimens, and they bring a unique look to your garden. Look for varieties like ‘Graham Blandy’, ‘Green Pillar’, or ‘Green Tower’, which all grow tall and slender. The Dee Runk Boxwood is also tall and very slim, and it’s a good choice too, with a reputation for durability.