Wildflower Wednesday: Nodding Onion

With Autumn bearing down upon us and two near frosts (0.5 C or 33 F) in the Home Bug Garden already, the thoughts of all optimistic Zone 3 gardeners turn to Spring. Well, really, one should be filling one’s basement with the famous Alberta green tomatoes first, but it is best to have one’s bulbs in the ground here as soon as possible and before the end of September for sure. Thus, another tardy Wildflower Wednesday is given impetus as I watch the frost on the garage roof dissipate in the weak Sunday sun.

 Although Alberta's current native flora can boast of about a dozen species that form true bulbs (essentially a buried bud composed of thick leaf and stem tissue), many of these are restricted to the extreme southwestern part of the Province. Most Albertan orchids, irises, and members of the Lily family (in the old sense) tend to overwinter as fat roots or rhizomes. The most spectacular exception is the Western Wood Lily (Lilium philadelphicum) that seems to do well everywhere except the prairie and the far north. One would think from the name that the Venus’ Slipper Orchid (Calypso bulbosa), a circumboreal inhabitant of coniferous forests, would also qualify, but leaf tissues seem to be missing from the ‘bulb’, so it is more likely a corm. Perhaps less spectacular are two species of Death Camas (Zigadenus elegans, venenosus) that cast their pallid pall across southern Alberta and three of the four species of Albertan wild onions (Allium).

 More than one hundred species of wild onions currently make their homes in America north of Mexico, although several of these are recent colonists and even weeds, e.g. the invasive Eurasian Wild Garlic (Allium vineale). Alberta has only four species, all considered native: Geyer’s Onion (A. geyeri), restricted to the SW mountains, and the more widely distributed Wild Chives (A. schoenoprasum), Prairie Onion (A. textile), and Nodding Onion (A. cernuum). The Home Bug Garden can boast two of these species: Nodding Onion and Chives. Native plant purists might challenge us on the Chives – var. sibiricum being considered native and var. schoenoprasum the introduced culinary Eurasian variant. However, since some chives came with the house, we may have both. Actually, a purist might even challenge us on the Nodding Onion. Our plants came from a sunny south slope of a glacial knob on our Moose Pasture 75 km to the east. It is quite likely that a century ago pondweeds, sedges, and cattails were the HBG native flora.

 As wildflowers go, though, Nodding Onion (Zone 2, sun to part sun, average to dry soil) is quite an attractive and interesting one and fits in well with other garden plants, at least on the border. The plants produce a tuft of strap-like leaves (~2-3 dm [8-12”] long) with an oniony taste and smell in May and the leaves persist all summer. The umbels of pink flowers are unlike most onions in that they dangle – the flowers are all upside down – seemingly making things a bit more difficult for pollinators. 

Interestingly, a study of Nodding Onion pollination on the coast of British Columbia, Schuett & Vamosi (2010, Evol Biol 37: 19-28) found that flowering at the same time as another wild onion or another Alliaceae, a starflower (Brodiaea), resulted in a decrease in the “quantity and proportion of conspecific pollen” being delivered by pollinators to the stigmas of Nodding Onion. That suggests to me that Nodding Onion may be being different on purpose, perhaps to keep the attention of bees that can learn how to pollinate difficult flowers. Schuett & Vamosi were more interested in theory than the natural history of Nodding Onion, but do mention that species of Andrena and Bombus were seen visiting the flowers. Bumblebees are known to be able to learn pollination tricks, so that is consistent with my hypothesis. Verbeek & Boasson (1995, Can J Bot 73: 723-727), however, have another hypothesis: nodding flowers are dodging the rain. They note that nodders (shooting star, some lilies, trout lilies, fritillarias, and Nodding Onion) in coastal British Columbia tend to bloom early when there is more rain. This would not seem to hold in Alberta (especially not this year – with the wet and cool weather continuing throughout the summer and into today). The central Asian Honey Lilies (once Allium, then Nectaroscordum, but now back in Allium) also dangle and some research (e.g. Dubouzet & Shinoda 1998. Theor Appl Genet 97: 541-549) supports a close relationship to Nodding Onion, so perhaps they may one day shine some light on the cause(s) of nodding (other than overly long blog posts).

 Nodding one’s umbels of flowers is an interesting behaviour, but what happens after pollination is even more interesting: the umbels become erect, assume a typical Allium exploding firework pattern, and seem to grow a bit larger too. Verbeek & Boasson report post pollination stem elongation as a general pattern in their meadow plants and explain it as facilitating seed dispersal. This seems to make sense to me and the addition of an attractive seed head is always welcome in a garden plant. Another advantage of Nodding Onion is that takes well to Green Roofs. One can find Green Roofs in British Columbia – the one on Vancouver Island with the goats is one of my favourites – but what with the extremely steep pitch to the typical Alberta home roof, weight of snow, and the intense winter cold - I can’t see them in my future. In Michigan, however, Getter et al. (2009, Urban Forestry & Urban Greening 8:269–281) found that Nodding Onion does very well on green roof plots with shallow soils (8-12 cm) and in sun or shade. So, perhaps some day I’ll get out the harness, ropes, and carabineers and start planting Nodding Onions on the roof. Not in the rain though. No matter how nice rain is for transplanting, this interminable rain of 2010 makes me want to stay indoors and away from slippery slopes and slugs.