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Garden Q&A: Who is the ‘father’ of a surprise crop of holly berries?

Q: My hybrid holly has a decent crop of berries this winter, which was a pleasant surprise since it didn’t berry well in prior years. I don’t think I did anything different this year in terms of care. I wonder, why is it suddenly fruiting?

A: The difference was probably pollination, either because the plant was better-pollinated this year or there is now a compatible pollinizer nearby where there wasn’t before. Hollies produce male and female flowers on separate plants. Female plants are the only ones capable of fruiting (producing berries), but usually only when pollinated.

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Within hollies, some cultivars can ripen fruit even without pollination, so are considered self-fruitful or self-pollinating when described in plant catalogs. (The latter term is technically incorrect since pollen was not involved, nor was any coming from the same plant. Parthenocarpic is the appropriate technical term.) Usually, though, fruiting is best when the female blooms receive pollen from another plant that creates fertile seed in the fruits.

Small bees and some flies pollinate holly, so there is a reliance on weather involved with pollination success any given year. Wet or cold weather can ground insects that need a minimum amount of warmth to fly. This might play a part in your plant’s lack of fruit in prior years, though it’s less likely to be the only factor if it’s happened several years in a row. Plant stress can influence fruiting as well. For example, individuals experiencing drought stress can shed unripe berries or even drop flowers, preventing fruits from forming that year regardless of how well pollination went.

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A prolific crop of berries on a female American holly.

We grow a wide variety of holly cultivars, both species and hybrids, in our gardens in Maryland. Though a few occur naturally, human-made hybrids are created by fertilizing the flowers of one species with the pollen of another. This can continue for several generations, resulting in a complex lineage for modern hybrid varieties. This might allow for easier pollination matchmaking since you could select from several different males as the potential pollen source to ensure fruiting on your female plants.

Generally, pollen from the same species is ideal for pollination, but as evidenced by the rampant hybridization, sometimes pollen from any of the parent species for a hybrid variety will suffice as well. Relatively few male cultivars of holly are grown by nurseries or gardeners since they offer less seasonal interest, but fortunately many of the female cultivars we plant are either relatively easy to provide a pollinator for or are self-fruitful and don’t need one. In your case, maybe a neighbor or someone living nearby planted a male cultivar that happened to be compatible with your female cultivar. Or, perhaps a wild American Holly male growing nearby is the “father” of a surprise crop of berries.

Q: I think a large woodpecker has taken an interest in one of my trees, though they never seem to finish making their nesting hole, even though new holes seem to appear regularly. Is their persistence a sign the tree is dying?

A: Woodpeckers consume insects that are living in the wood, though these are not always insects that caused the tree any serious damage. (The insects may be living in wood which is already dead or dying from other causes.) Small downy woodpeckers, for instance, seek out insect larvae tunneling just under the bark (plus insects hiding underneath loose bark flakes for winter shelter), whereas the bigger pileated woodpeckers excavate larger hollows to get at carpenter ants nesting deeper in the heartwood. This sounds like what might be happening in your case — the holes are not the abandoned beginnings of nest cavities but are instead access points drilled for feeding.

Gardeners sometimes blame carpenter ants for killing a tree, but in actuality the ants generally move in when a tree’s heartwood is already accessible and softened by moisture intrusion or wood decay. Since heartwood is already naturally dead tissue, this ant excavation doesn’t threaten the tree’s life directly, though it might make it less stable in a storm. If the tree’s canopy looks normal so far, there probably isn’t a serious issue present. If borers are damaging the tree just underneath the bark instead, often canopy decline is evident by the time such pests are abundant, so while you can’t do much about it at that point, at least it would be more clear as to why the birds are foraging there. Worst-case, if a tree is in decline, it can still offer great wildlife value (and a lot of other forest creatures rely on woodpecker excavations) and is worth keeping for this reason if it’s not a hazard.

University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Extension” to send questions and photos.


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