Winterberry (Ilex verticillata) A Favorite Native Landscape Plant

Although this winterberry (Ilex verticillata) has only a few
berries remaining, the winterberry is widely used in
wreaths and decorative holiday arrangements for its
winter color.
Photo by Brad Sylvester. Copyright 2011. Do not copy.

Driving along the back roads of New Hampshire in the fall after the leaves have dropped, it is not unusual to see the otherwise bare branches of the winterberry (Ilex verticillata) bedecked with bright red berries. In fact, you'll often see cars stopped near these wild, native shrubs clipping off the branches with the festively colored berries to weave them into homemade wreathes or to simply arrange them in vase as a holiday decoration. Winterberries are actually a species of holly plants as are all members of the Ilex genus.

I did not think that there was any winterberry growing on my property, but while taking a walk through the woods yesterday, I noticed a few dozen red berries on a thin tree-like plant that stood about 6 feet high. Winterberry! As you can see from some of the pictures on this page, it was growing in what I might call a vernal pool, if it were spring. Since it is December, however, I'll call it a wet, low-lying area flooded by recent rains and snow-melt located in the forest about twenty feet away from the edge of a stream bed.

Two small winterberry shoots can be seen to the right of
the larger main stem emerging from runner roots that
travel underground.
Photo by Brad Sylvester. Copyright 2011. Do not copy.

As you can also see from the picture on the right, the forest floor there is covered in this year's fallen leaves and pine needles. The decay of leaves and evergreen needles tends to make soil acidic, which is actually preferred by the winterberry. It also prefers very moist soil such as that found along roadside ditches, river banks, lake shores, and wet, low-lying areas in the middle of the forest.

Winterberry is shade tolerant and will grow in areas of only partial sun, such as the middle of a forest where I found this one. It will grow, much fuller and bear more fruit if it is placed in full sun since it will be able to harvest more energy from the sun which it uses to grow, flower, and fruit.

Actually, though, not all winterberry plants fruit. The plant has both male and female sexes and it is only the female plants that will produce the bright red berries. In order to do that, however, they need to be pollinated by a male winterberry plant. If you have one on your property that does not flower, then it is either a male plant, or a female plant without any male winterberry plants nearby.

Aside from the berries, which grow off the sides of young branches as shown in the pictures, the bark is a useful identification marker in the winter as well. The trunk and branches have horizontal lenticels, much like a birch tree, that break up the smooth bark. A lenticel, as we are reminded by this Cornell University publication,  is an area that allows the  plant's inner bark to "breathe," by providing permeable openings in the bark of the winterberry, which would otherwise not allow gas exchange.

In the spring, the winterberry has tiny, yellow-green flowers, which will become green berries on the female plant if pollinated. The green berries ripen around late October, turning a vibrant red. The red berries will stay on the branches through most or all of the winter, providing eye-candy for humans and a more nutritious treat for many wild animals. The USDA says as many as 48 species of birds eat the fruit of the winterberry plant as do white-tailed deer, moose, snowshoe rabbits and cottontail rabbits, as long as the latter two can reach the berries, often aided in their reach by walking atop deep snow. Winterberry plants can reach as high as 8-15 feet in height.

Propagating Winterberries

Winterberries, like many wild plants, have redundant systems of reproduction. They have fruits that contain seeds, of course, but they also send out runners, roots that travel underground and surface periodically with a new plant, like lilacs and many other shrubs. With human intervention, cuttings can be taken and rooted to make new plants as well.

Seed Propagation of the Winterberry Plant

Winterberry fruit (Ilex verticillata) and two seeds
Photo by Brad Sylvester, copyright 2011. Do not copy.

Of the three methods only the seeds produce new plants which contain a mix of the genetic material between the pollinating male plant and the fruit-producing female plant. Each berry contains 3-5 seeds each with a hard outer shell. That shell protects the seed as it travels through the digestive system of birds or other animals that eat the berries. The bright red fruit that is easy for birds to find helps ensure that the seeds are widely dispersed. Presumably, if the bird that found the berries prefers the same habitat in which it found the winterberry plant, then it will deposit the seeds, or most of them, in the plant's favored habitat although that may be far away from the parent plants.

Winterberry seeds do need to be cold-conditioned before they will germinate effectively. That means either leaving them outside and collecting them in the spring to be planted, or collecting them in the fall and winter from the ripe red berries and placing them in the refrigerator (not the freezer) for a period of 45 days or more before planting them as you would any other seed. Plants grown from seed may turn out to be either male or female plants, there's no way for the average gardener to choose, or even tell which it is until the plant is several years old and becomes sexually mature.

• Read more about cold conditioning seeds here

Winterberry Propagation by Runner Shoots and Cuttings

The runner shoots can be dug up after the leaves have dropped off the winterberry plant and it has gone dormant for the winter. The third method of propagating winterberries is to root cuttings. This is done in the spring (May-June) when the plant is primed and in growth mode. Using either of these propagation methods will result in new plants that are exact genetic copies of the plant from which they were taken. That means they will even be the same sex so plan accordingly and remember that you'll need at least one male, pollinating plant near the female plants if you want them to produce berries.

I'll write up and link some complete guides to various types of propagation, as well as handling and transplanting tips and link from each appropriate plant on this blog soon. --Follow this blog now with either Networked Blogs or Google Friend Connect (found in the margins of this page) if you don't want to miss it.--

In the spring, I'll definitely take some cuttings from this winterberry plant and add a few new plants to the more landscaped part of my yard along the stream bed in the back yard. Because winterberry is a native plant to the area and will be planted in the type of soil and conditions that it prefers. It is an eco-friendly choice for New Hampshire home-owners, requiring neither extra watering nor special pesticides or fertilizers to thrive here.

Propagating Perennials from Seed: Cold-conditioning

Many of the pereennials we choose to keep in our yards are selected for their beautiful flowers. Whether we're adding a spash of color to a border area of our yard or building a complex web of colors in our gardens, perennials offer just what we need. Once we have one that we really like, we often want to add more of the same variety. There are several ways to propagate perennials, for this blog entry, I'm going to talk about seed propagation.

Flowers exist to make seeds. That's what they're for as far as the plant is concerned. Bright colors or attractive scents are just tools to make the flowers better at producing seeds. Color and scent attract pollinating insects or birds to fertilize the flowers by transferring pollen from the anther to the stigma of either a different flwoer or within a single flower.

Once a flwoer is pollinated in this way, the pretty petals are no longer useful to the plant so the plant stops using up energy to maintain them. The dry up and fall away leaving behind the grwoing seeds. Seeds may either be encased in some sort of pod, as in the California poppy or may grow individually as they do in the cone flower. In any case, once the flower dies off, the plant diverts energy to the growth of the seeds themselves.

Gardeners who want the plant to continue flowering for a longer period of time can make the decision of where to send energy for the plant. By cutting off the flowers as they begin to fade and wither, a process called dead-heading, the gardener can stop the plant from expendign it resources on seed growth. Instead, many plants, detecting the lack of viable seeds, will rush to produce more flowers to start the seed-producing process all over again before autumn sets in.

Those who want to gather seeds from their perennials to produce even more plants next year, therefore, should not dead-head the spent flowers. Even though more flowers might grow later, the plant should have more energy earlier in the year and the first batch of flowers and seeds should mature faster and be more prolific and hardy.

When the seeds look all dried up they are ready to harvest. For those growing in pods like the iris or poppy, the top of the pod may "pop," providing a way for the seeds to exit the pod. Collect the seeds and carefully label them if you are going to save them until spring planting or start them indoors.

Seeds collected from many perennial plants adapted for northern climates will not grow if planted indoors immediately or if kept indoors until spring. Think about it. If these seeds were ready to sprout as soon as they matured, most would start growing in the autumn after a late summer rain or during a warm week in late Spetember or October. This would mean the plants would be fragile and tiny seedlings when the frost and killing freeze hit them.

The would not have strong root systems or stores of energy saved up from rampant leafy growth phase that often occurs in the parent plant after the seeds have matured. In other words, they would not have the stregnth or energy to survive the winter and spring up again whne the ground thaws and the warm weather returns the following year.

Plants have adapted to the climate over millions of years and have solved this problem in a variety of ways. One of the most common ways that seed-producing plants in northern climates have overcome this obstacle is to produce seeds that will not sprout until they have been cold-conditioned, or spent some time in winter-like temperatures. Extended periods of cold are required to "prime" the seeds or trigger them to respond to favorable growing conditions.

Failure to cold-condition seeds harvested from garden plants is one of the main reasons for very low yields or complete lack of germination. Fortunately, armed with a little knowledge, gardeners can cold-condition perennial seeds to make them ready to plant.

This can be done in two ways. First, seeds can be cold conditioned the natural way. You can scatter or plant them in the fall before winter to allow them to be cold-conditioned by the winter termperatures. This will generally work fairly well. After all, if left to its own resources, it's how the plant would handle the matter itself. On the other hand, look at the number of seeds most plants produce and ask youself why your yard isn't completely overrun with wild flowers. Each poppy flower produces hundreds upon hundreds of seeds, but you don't wake up one spring morning to find five or ten thousand new poppy plants growing in your yard. That's because many of the seeds don't survive until spring.

Why not? Well, many reasons. Insects, birds, or rodents may eat them in the fall, the spring or even during the winter itself when other food is scarce for winter birds or those few rodents that don't hibernate. They may succumb to fungal infections or rot if they stay too wet for too long. They may be lying on top of the ground exposed to extrememly cold temperatures that test them beyond their cold-resistant properties. Perhpas they simply fall on a patch of ground that is not conducive to plant growth. Some few may even try to sprout without cold-conditioning, dooming them to an early demise.

Still, enough survive to ensure the continuation of the species, so leaving them to endure the winter can be a successful propagation strategy. The up side of this approach is that the seeds decide when to start growing in the spring. When the soil is warm enough, has the right level of moisture, and there is enough sunlight in the day to ensure the young seedlings have the best chance at survival, they will sprout on their own and begin to grow. This way, they are automatically hardened off to outdoor conditions.

To cold-condition perennial seeds this way, harvest the dried seeds from the plants in the fall or as soon as they are ready. Decide where you want them to grow next year. Clear other plants that may already be growing there so the new sprouts will have less competition form stronger more mature plants. This may means digging or pulling up roots as many wild perennials will propagate from even small pieces of root.

It doesn't have to be a perfect process, but the more of the existing plants that are pulled, the better chance the need seeds will have in the following spring. Then, after the first few frost, simply scatter the new seeds over the prepared plot. Do not water them in. Remember, the plan is for them to remain dormant until spring. All that water will do at this point is reduce the viability of the seeds.

The other method of cold-conditioning perennial seeds is to keep them in the refrigerator for at least 45 days. The refrigerator temperature is cold enough to convince the seeds they have made it through an actual winter. However, the danger of this method is dehydrating the seeds. The cold air of the refrigerator will suck every bit of mositure out of the seeds, killing them in the process. 

To prevent this, pack them as you would pack food to prevent freezer burn. You can place them in a double-sealed freezer bag or an air-tight tupperware type container. You don't want too much moisture in the container or too much air. Once they have served their sentence in the fridge, the seeds can either be planted outdoors, or started indoors before it's warm enough to plant outdoors. Just remember that if you do start them indoors and want to transplant them outdoors, you'll need to harden them off, or gradually accustom them to the harsh rays fo the sun and the extreme hot and cold temperatures they may face once they are outside.

The second method, properly executed, should result in a much higher yield percentage for a given quantity of seeds. In other words, if 2-3 percent of the seeds survive and grow if left to fall from the parent plant and cold-condition in place, you might get as much as 80% or more germination from seeds harvested, cold-conditioned, and sprouted indoors.

Not all the perennial plants in your garden require cold-conditioning, but those well-adapted or native to northern climates likely will benefit.