By William Scheick
Among botanists, hollies still raise many unanswered questions. Least understood are both the extent and the limitations of cross-pollination among hollies.
Relatively rare leaf-shedding (deciduous) hollies, including possumhaw (Ilex decidua) and common winterberry (I. verticillata), are less scientifically documented than the more prominent evergreen hollies, including yaupon (I. vomitoria). Even Fred Galle’s extensive taxonomic book titled Hollies only mentions sketchy “reports of” certain hollies successfully cross-pollinating or failing to cross-pollinate.
So when it comes to using these three Texas native hollies in our landscapes, we are counting on a certain amount of good luck with “berry” (drupe) production by female plants. Most of the time we do quite well because our purchased female hollies get required pollen from unseen suitable/compatible male holly donors located somewhere else.
When thinking about native hollies, notice how often the most impressive displays you have seen were plants in open spaces. Fenced-in or crowded plants have less of a chance of being pollinated by some compatible male holly on someone else’s property. Even landscaped yaupon hollies will over time lean farther and farther away — an allelopathic response — from an encroaching neighboring plant. Location, location, location.
Be sure, too, that hollies are not situated downhill from lawns that are fertilized or (worse yet) treated with other chemicals. I have seen people accidentally kill foundation plants by failing to notice that heavy rains on treated lawns result in chemical impacts on nearby plants. Too much nitrogen, for instance, will stimulate hollies (and many other plants) into stem- and leaf-production at the cost of flowering/fruiting. This could be a factor for one frustrated grower of berry-less mature possumhaws sprouting only “new growth all over the place.”
Besides location, enticing bees to your hollies is important. Bees are holly pollinators, but bees are hardly plentiful these days in my experience in the Austin metroplex. Substantial companion plantings that attract bees would benefit nearby native hollies.
Drought is also a factor, not only in the reduced number of bees but also in the reduced number of holly berries. Drought can cause male blooms and compatible female blooms to emerge at different times rather than at the same time, and this lack of synchronicity would mean little-to-no pollination.
Drought can cause premature berry-drop, though the fruits are so small that the typical viewer might not likely notice. Hollies are tough and can withstand drought, but forcing them to expend their carbohydrates during survival mode will result in little-to-no berry production. In the wild, Texas hollies tend to prefer thickets along streams, a fact suggesting that these plants will be more likely to produce berries with some hydration to ease the effects of droughty conditions. After all, berries are like watermelons in that they contain a high percentage of water.
Droughts also cause animals to forage for the moisture in fruits that they might normally ignore during better times. Sometimes this means that holly berries disappear while unripe and before we get to appreciate them. On the other hand, it is helpful to hollies when birds consume ripe berries later on in the season, thereby making branch-space for next year’s flowers.
Seasonal bad luck with hollies includes a late freeze that destroys holly blooms to a heavy population of grasshoppers that devastates the berries. And although you might not catch them doing it, some dogs (my huskies, for example) don’t eat the toxic berries but do delight in nipping them off one at a time just for fun.
Texas native hollies are highly adaptable as home landscape plants in bush or tree form. So most of us, thankfully, have trouble-free experiences with them. Even so, sometimes hollies can be a bit persnickety — not as badly as my huskies, but still… Some hollies will exhibit a quirky behavior known as “cycling,” which refers to periods when a plant function (such as flowering or fruiting) clicks off for a time or skips a year or two for reasons not at all perfectly obvious to us.
Which returns me to my starting point: hollies still raise many unanswered questions.