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Garden Q&A: Mistletoe - it’s not just for the holidays

Q: When I drive around on the Eastern Shore in winter, I see clumps in some of the tree canopies that puzzle me. Not only do they look a bit green, but there’s too many for them to be squirrel nests. What might they be? Are the trees OK?

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A: It’s everyone’s favorite plant parasite — mistletoe! (Well, there are a number of parasitic plants that grow in Maryland, and their blooms can be quite interesting, so picking a favorite is hard.) It’s fun to realize something that seems so seasonal and exotic is actually quite local and with us all year long.

While there are multiple species in the U.S., our local one is American mistletoe (phoradendron leucarpum) and is predominantly found on our coastal plain on both sides of the Chesapeake Bay. Technically they are hemiparasites, which means they only partially depend on stealing nutrients and water from the tree’s vascular system; they can photosynthesize the rest of the carbohydrates they need, which is why they retain green foliage.

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Although impacts on the host trees vary with mistletoe species, they rarely cause tree death directly. Instead, a high population in a single tree might sap its vigor and contribute to a relatively early demise, but decline can take decades. Dead snags still provide great resources for forest animals. For example, a U.S. Geological Survey article about mistletoe mentions cavity-nesting bird populations have been found to be three times as high in forests with abundant mistletoe, since they have access to more nest sites.

Overall, American mistletoe is quite a beneficial member of this area’s natural ecosystem, providing early-season flowers for bees, serving as a host plant for the state-rare great purple hairstreak butterfly, and providing food and shelter for an array of bird and mammal species.

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Q: My spicebush hasn’t produced berries yet, and it’s several years old, so I think it’s mature enough. Am I missing something?

A: There are three possible reasons for this — two as to why it can’t fruit and a third as to why berries aren’t maturing.

Spicebush (lindera benzoin) produces male and female flowers on separate plants. This trait is shared by several other garden plants, including holly, bayberry , asparagus, ginkgo, juniper, yew, and persimmon. Male-flowered plants provide pollen but cannot fruit. Female-flowered plants produce berries if they’re pollinated.

Part of the problem is knowing which you have. In some species it’s hard to differentiate between flower sexes without magnification, and essentially impossible after bloom when fruit is lacking. Cultivars are usually of known sex, helpful when you either want berries (think: winterberry holly) or don’t want berries (think: asparagus, because it detracts energy from future harvests). Spicebush cultivars are scarce. Seed-grown individuals or plants of unknown parentage (if, say, a cutting was propagated from an unsexed plant) are potluck, so you either wait-and-see or plant several in the hopes that you have at least one of each.

If your plant is female, it needs a pollinator for berries. As with many fruiting shrubs, spicebush is insect-pollinated. Depending on how far they travel in their foraging, they may not have had spicebush pollen to collect before visiting your plant’s blooms. If there are wild spicebush nearby, perhaps the weather wasn’t cooperative. Pollinators are grounded when it’s chilly and/or rainy, and spicebush does bloom fairly early in spring. In that case, you’d just have to wait for a more cooperative spring with milder or drier weather.

Lastly, plants under stress will abort developing fruit as a measure of self-preservation — they have to conserve what resource reserves they have if there isn’t enough to both keep the plant alive plus finish ripening the fruit. Drought stress is a typical trigger. Fruits that weren’t well-pollinated also may start forming and then disappear (usually falling off unnoticed because they’re still green and small). Hollies are notorious exhibitors of both drought- and pollination-related berry drop. Spicebush thrives in woodland conditions, so if its needs are being met and growth looks normal, a female plant should fruit in due time.

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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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