How-To · Holly Pollination · Southeast

The Holly That Stands Bare in December

Every winter someone writes to us about a holly that flowers faithfully and fruits never. The answer is almost always the same, and almost always fixable, though the fix takes a spring to show.

9 min read · By Fiona von Grey · Aiken, South Carolina

IThe December complaint

The letter arrives in the second week of December, and the wording barely changes from year to year. A holly was planted five or six seasons ago, specifically for the berries. The shrub is healthy. The leaves are glossy. Every spring there is a modest, sweetish flowering that the bees find before the gardener does. And every December the branches are green and bare, while the neighbor's holly, planted the same year and never once fussed over, is loaded to the point of sagging.

The usual assumption is that something has gone wrong: wrong fertilizer, wrong pruning, wrong soil, wrong luck. In practice the plant is doing exactly what the plant was built to do. The gardener has simply bought half of a holly.

IIA genus that keeps the sexes apart

Nearly every holly is dioecious, from the Greek for two households. Male flowers and female flowers are borne on separate plants, and no amount of good culture will persuade a male holly to fruit or a lone female to fruit without pollen. Only the female carries berries, and only after a male has bloomed within range of the same bees.

This is not obscure botany. What makes the problem so persistent is that the two sexes are nearly indistinguishable at the garden center, in leaf, in habit, and on the label. A one-gallon Ilex verticillata in May looks the same whichever household the shrub belongs to. The difference shows for perhaps ten days a year, in flowers a quarter of an inch across, greenish white and easy to walk past.

Both sexes flower in spring, in the leaf axils of the current season's growth, which is worth holding onto: next winter's berries are riding on wood that has not yet been made. Male flowers are usually solitary in the axil and obviously stamened, a small crown of pollen-bearing filaments around a vestigial center. Female flowers sit in small clusters, called cymes, and carry a plump green ovary in the middle, ringed by stamens that carry no viable pollen at all. Once you have seen the green bead at the center of a female flower, the distinction is unmistakable forever after.

How to sex a holly in bloom, without a hand lens

Pick a single open flower in mid spring and turn the face toward the light. If the center is flat and the whole flower reads as a fuzz of stamens, the plant is male. If there is a distinct green dome in the middle, the size of a pinhead, sitting proud of the stamens, the plant is female. On a female you will also find the flowers gathered in twos and threes along the new shoot rather than sitting singly.

The blunter method works just as well: wait until autumn. A holly with fruit is female. A holly with no fruit, in a garden where other hollies are fruiting, is almost certainly male.

The gardener has not failed the plant. The gardener has bought one household and expected two.

IIIMatching the bloom, not just the species

Buying a male is the first half of the answer. Buying the right male is the half that gets skipped, and where the deciduous hollies punish carelessness hardest.

The winterberries, Ilex verticillata and the hybrids with I. serrata, have been selected over decades for flowering time as much as for fruit color, and the named males were bred to bracket the season. 'Jim Dandy' is an early male, opening in the window that suits early females such as 'Red Sprite' and 'Maryland Beauty'. 'Southern Gentleman' is a late male, cut to the bloom of 'Winter Red' and 'Winter Gold'. Pair an early female with a late male and you get what everyone dreads: two healthy shrubs, both flowering, missing each other by a fortnight, and a bare December.

The overlap does not have to be perfect. More overlap simply means more fruit, and a partial overlap gives a partial crop, which is why a mismatched pair sometimes produces a thin scatter of berries and convinces the gardener that the problem is nutrition.

Female winterberry	Bloom window	Male to plant with
Ilex verticillata 'Red Sprite'	Early	'Jim Dandy'
Ilex verticillata 'Maryland Beauty'	Early	'Jim Dandy'
Ilex verticillata 'Winter Red'	Late	'Southern Gentleman'
Ilex verticillata 'Winter Gold'	Late	'Southern Gentleman'
Ilex 'Sparkleberry' (verticillata × serrata)	Late	'Apollo' or 'Raritan Chief'

The evergreen hollies are more forgiving. Ilex opaca, I. vomitoria, I. cassine and I. coriacea flower over a longer, sloppier window, and a male of the same species planted anywhere in the vicinity will generally do the job without a named cultivar and a calendar. Cross-species pollination happens too, more readily than the tidy literature suggests, which is why the neighbor's unplanned holly sometimes carries the whole street.

IVHow far is too far

Holly pollen moves on insects, chiefly bees, and the practical range is generous but not infinite. The working figure most extension services give is one male within about fifty feet of the females, and one male for something between three and ten females depending on how heavy a crop you want.

The studies are blunter than the garden advice. Fruit set in holly has been measured falling from roughly ninety-five percent at forty meters from the nearest male to about thirty-five percent at a hundred meters. Bees will carry pollen much further than fifty feet when the foraging suits them, so distance is a gradient rather than a wall. A male at the far end of the garden will give you some berries. A male inside the same bed will give you the crop you paid for.

Siting has a second, quieter benefit. A male holly is a perfectly good plant in every season except the one everyone cares about, so the usual move is to put the male behind the females, or at the back of a mixed screen where the winter bareness of a deciduous male reads as background rather than absence. The columnar yaupon Ilex vomitoria 'Will Fleming' solves this neatly for the evergreens, being a strictly narrow male that works as a vertical accent and a pollen source at once.

VWhen pollination is not the problem

Before rearranging the garden, rule out the three other honest causes of a barren holly.

A late freeze. Hollies flower in spring, and a hard frost landing on open bloom will take the crop for that year outright. A single berryless winter on a shrub that has fruited before is almost always weather, not sex, and the following season usually corrects.

Drought. Berries swell through late summer and early fall and need water moving into the fruit continuously. A holly under real drought stress will shed developing fruit rather than carry what the plant cannot supply, and the tell is wrinkled, undersized berries dropping in August and September rather than a clean absence from the start.

The pruning. Because flowers form on the current season's growth, a holly sheared hard in late spring is a holly whose flower wood has just been carted to the compost. Hedged hollies fruit poorly for exactly this reason. Prune in late winter, before growth begins, and take whole branches rather than shearing the surface if fruit matters to you. The cut stems are worth having indoors, and we have written elsewhere about harvesting and conditioning woody cut stems so the berries hold.

Birds are the fourth cause and the one nobody should try to fix. Cedar waxwings can strip a mature Ilex opaca in a morning, which is the entire ecological point of the fruit.

VIThe exception that proves the rule

There is one famous cheat. Burford holly, Ilex cornuta 'Burfordii', sets a heavy crop of fruit without pollination at all, a condition called parthenocarpy, and the dwarf form behaves the same way. A Burford planted alone in a courtyard will still fruit, which has made the cultivar a fixture of Southern foundation plantings for the better part of a century and has quietly taught two generations of gardeners the wrong lesson about the genus.

The trait is worth knowing about, and worth not generalizing from. Burford is the exception in a genus of several hundred species that otherwise holds firmly to two households.

VIIWhat to do about a barren holly this fall

Fall is the right season to fix this in the Southeast, because fall is when hollies go in the ground here and because the diagnosis is easiest while everyone else's hollies are visibly fruiting.

Walk the garden in December and mark which hollies carry fruit and which do not. Identify the species you are dealing with, because the male you need is species-specific for the deciduous hollies and roughly species-specific for the evergreens. Then plant one male of the matching species, and for winterberry the matching bloom window, within fifty feet of the females, ideally closer and ideally behind them. Water the new plant through the first summer so the roots are established before the first flowering that matters.

Then wait. A male planted this autumn flowers next spring and delivers berries the following December, which is a long wait by the standards of most garden problems and a short one by the standards of hollies. The shrubs will outlive all of us.

What if I cannot add another plant

Two workable tricks. A branch of male holly in bloom, cut and stood in a bucket of water beneath a female in flower, will pollinate a small shrub adequately for one season; nurseries and holly societies have done this for decades and it is less absurd than it sounds. Failing that, a male can be grafted into an existing female, which gives you one household in two on a single set of roots. Neither is a substitute for a second plant, but both will get you a crop while you decide.

Do the native evergreen hollies need this too

Yes. Yaupon (Ilex vomitoria), American holly (I. opaca), dahoon (I. cassine), inkberry (I. glabra) and large gallberry (I. coriacea) are all dioecious. The difference is that in much of the Southeast these species grow wild in the surrounding country, so an unplanned male in a fencerow half a block away is often already doing the work. Gardens in new subdivisions, cleared lots and coastal developments are where the absence bites, because the wild population was scraped off before the houses went up.

If you want the wider picture of the genus rather than the mechanics of fruit set, our North American guide to hollies walks the species one by one. For the strangest fruit color in the group, see the yellow-berried yaupon 'Yawkey'. And for the holly nobody grows for berries at all, there is yerba mate, grown for the leaf and drunk by half a continent.