It’s difficult to walk past Winterberry Holly (Ilex verticillata) when it’s in fruit without noticing it. The abundant, vividly red, globular, fleshy fruits of this aptly named shrub never fail to catch the eye.
Where do all of those luscious-looking fruits come from?
Have you ever noticed Winterberry Holly in bloom?
In late spring, Winterberry Holly is covered with an equally large number of somewhat inconspicuous greenish-white flowers. The flowers bloom gradually over a period of a few weeks.
Like all hollies, Winterberry usually has male and female flowers on separate plants. Only female flowers can develop fruit. Although it isn’t typical, there may occasionally be a specimen with male and female flowers on the same plant, or some flowers that are perfect, that is, they have both male and female parts. Plants often have some variation, as they continue to evolve to try to find the most effective and efficient survival strategies.
Female flowers are usually in small clusters of up to three. The flowers have a single pistil (the female reproductive part) at their center. The green rounded base of the pistil is the ovary. If a flower is successfully pollinated, the ovary will mature, becoming the bright red fruit we see later in the season. The ovary is topped by a stigma, where pollen must be deposited in order for pollination to occur and fruit to develop.
The white arrow- or spade-shaped projections in between the petals of the female flowers are sterile stamens; they don’t produce pollen that can fertilize the flowers. It’s likely that they help attract pollinators. As these sterile stamens age, they turn brown.
Male flowers often bloom in crowded clusters of up to 10 or more. The male reproductive parts, called stamens, reach upward from the face of the flower, the anthers at their tips ready to deposit pollen on a flower visitor.
Winterberry Holly needs third party assistance to move pollen from a male flower on one plant to a female flower on another plant, in order to achieve pollination. It may be easy for people to walk past without noticing when these shrubs are in bloom, but fortunately the flowers are enticing beacons to potential pollinators of many different species, especially bees. A recent study showed Winterberry Holly to be among the most attractive to bees of the flowering shrubs.
In my own garden I spotted Bumble Bees, Mining Bees, Sweat Bees, Small Carpenter Bees and a wasp visiting the flowers for nectar rewards. Bees also eat pollen, and female bees may collect pollen to feed their larvae.
Without the assistance of these flower visitors, pollination would not take place, no fruit would develop, and Winterberry Holly would not be able to reproduce. If these pollinators do the job the plants have enticed them to do, fruit develops, ripening by fall.
Birds are the primary target audience for the colorful display of Winterberry Holly’s bright red fruit. Many different species of birds including Eastern Bluebirds,
and Hermit Thrush
eat the fleshy fruit and later become the unwitting dispersers of the seeds inside as they deposit them with natural fertilizer when defecating.
Small mammals like mice and squirrels may eat Winterberry fruit, too. People are just the accidental beneficiaries of the bright spectacle, but shouldn’t eat the fruit, which is toxic to humans.
Winterberry Holly fruits contain more carbohydrates than fats, making them less preferred by birds than some other fruit available in the fall. As a result, Winterberry fruit is frequently passed over until later in the season, often well into winter, although sometimes a flock of hungry American Robins or Cedar Waxwings will strip a Winterberry Holly of all its fruit in a matter of hours.
Winterberry Holly is a deciduous shrub or understory tree that grows to a maximum height of about 15 – 20 feet (5 – 6 meters). It prefers moist soil, and is indigenous in bogs and wet woods in the eastern half of the United States and Canada. It makes a great addition to your own landscape for its benefit to pollinators, birds and other wildlife. It doesn’t hurt that Winterberry Holly adds some bright color to a winter landscape.
Eastman, John. The Book of Swamp and Bog. 1995.
Eaton, Eric R.; Kauffman, Ken. Kaufman Field Guide to Insects of North America. 2007.
Mach, Bernadette M.; Potter, Daniel A. Quantifying bee assemblages and attractiveness of flowering woody landscape plants for urban pollinator conservation. 2018.
Rhoads, Ann Fowler; Block, Timothy A. The Plants of Pennsylvania. 2007
Williams, Paul; Thorp, Robin; Richardson, Leif; Colla, Sheila. Bumble Bees of North America. 2014.
Wilson, Joseph S.; Carril, Olivia Messinger. The Bees in Your Backyard. 2016.
Missouri Botanical Garden Plant Finder
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Thanks Mary Anne. I love all that information and the wonderful photos!!
I enjoyed this & will share. I planted a male & female winterberry, together,10 years ago, I seldom if ever get fruit. I ordered a “pair” of tall ones & a male & several females of the shorter varieties, which produce lovely berries. I will closely observe the pair of tall ones & check to make sure they have obvious male & female flowers. The shorter varieties are close to my entrance, so I observe them more often & know that the male blooms before the females & both are quite late to out of dormancy & bloom.
Even if the taller pair are one male and one female, if they aren’t blooming at the same time, pollination won’t occur. I’m glad you enjoyed the post! Thanks for sharing.
According to my vet, winterberry is poisonous to dogs & cats
That may be true. The fruit is toxic for humans, too.
Great post! Cheers!!!
Thanks, Deedee! Happy new year!
Thank you, Mary Anne! We planted winter berries last year and got a beautiful crop from the female. We appreciate your filling our knowledge of this lovely pollinator attractor! Bill & Dot
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It’s a beautiful shrub, and great for birds, too!
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So interesting and beautiful! I love the pictures and descriptions of the male and female flowers.
Wow. Thanks for sharing all of that fascinating information about winterberries and your wonderful photos.
Thanks, Mike! I’m glad you enjoyed the post. Happy New Year!
In fall 2019 I planted a winterberry bush in each of the flower pots by my garage with the intension of having fresh berries on on the bushes for Christmas 2020. I bought my bushes at Shady Brook Farm in Yardley. The bushes contained the male and female on the same bush. Tiny bees pollinated the bushes. I had beautiful red berries before Thanksgiving but one morning all the berries were gone. I think a squirrel might have eaten them. I saw the squirrels eating my beauty berries. I then bought winterberry for decoration and no one is eating the berries.