Viburnums pollination, propagation, provenance: Oh my!
There have been many excellent discussions about viburnums here on Shrubs forum, as well as elsewhere like Natives and Wildlife forums. Some of them have gotten to be voluminous, and have a lot of good collateral info. I wanted to summarize my thoughts/opinions about the rationale of pollination in viburnums. This same info is posted on the "Still about Viburnums: berries" thread on the Wildlife forum. Speaking of voluminous: stop now if you don't have your athletic reading shoes on.
Many posts on GW are hitting all around the concept of the conditions necessary for fine fruiting. I'm looking to provide some clarification of what I think most people are looking for, information-wise. I use Viburnum dentatum (arrowwood) as the example, because it is a widely used plant that most folks have heard of and is easy to grow.
FIRST: there are some claims that the only reason that anyone says you need two different plants with viburnums is so that they can sell you something. Hogwash. University professors, researchers, and people on GW don't have a financial interest in your garden. You can send me money if you want; I'd rather see you post (by this fall) that your viburnums are loaded with fruit because you installed several dissimilar individuals. And then you could send me some for my collection....
NEXT: Viburnums are monoecious, as has been stated elsewhere and can be looked up in texts. So are most of the Rosaceae family (Malus, Prunus, Pyrus, Amelanchier, Rosa, etc.) but many fruit tree growers will vouch for increased fruit production when multiple clones of a species are planted in proximity in order to provide cross-pollination opportunities. This implies (and researchers/scientists/someone besides me can verify better) SELF-INCOMPATIBILITY of individuals despite each plant having perfect flowers. This doesn't mean that a plant CANNOT pollinate itself, just that it does very little or poorly. There is anecdotal evidence (here on GW, and elsewhere) of some solitary plants of some species of viburnums that produce decent fruit crops, but it is so easy to plant a couple different ones that it defies logic not to. Co-opt a neighbor or some such if you don't personally have room.
NEXT: The biggest confusion I observe is the issue of species versus clone or cultivar. The best way to resolve this is to do a little reading in a biology or botany text, but I'll endeavor to layman-ize it. When someone says "I have the species Viburnum dentatum, not any clone" what they are saying is that they have an unnamed or unknown plant of arrowwood, not a named plant of arrowwood like Chicago Lustre. What they don't say (and maybe don't know) is whether they have a seedling of Viburnum dentatum. THAT MATTERS. If they know they have a seedling (grown from seed, not just a little plant), then they have a genetically distinct individual of Viburnum dentatum from a known provenance. If they just have an unnamed plant, it could just as well be a clone depending on propagation method. And on we go...
NEXT: Propagation....every Chicago Lustre is (should be) identical to every other Chicago Lustre because the plant is reproduced VEGETATIVELY (clonally or asexually), generally from cuttings that are then rooted. Species plants of arrowwood can also be produced this way. This is the trap that many individuals seem to fall into, in these threads, when claiming that they have "the species" and not necessarily knowing if they have seedlings or simply unnamed but clonally-produced plants. When plants are produced from seed (SEXUALLY) this means that there has been some genetic mixing between two parent plants resulting in seedlings that are related to but not identical to the parent producing the seed. Individually, these seedlings are no more or less capable of self-pollination. Are you worn out yet?
If you purchase and plant more than one arrowwood that were grown from seed (thus similar but not identical), then these will be fine for providing cross-pollination conditions if they have overlapping bloom times, which they should if from the same seed source.
NEXT: There was a GW question elsewhere about what happens when buying plants from Oregon and from North Dakota sources. This was one of the best ones yet about getting to the crux of the matter. Overlapping bloom times is the critical factor. If plants from these disparate sources bloom with a month separating them, no dice. If they overlap, one should have oodles of fruit.
NEXT: Provenance is important, especially to northern gardeners and those who want to respect their efforts to reinvigorate native landscapes. You want a plant that is known to survive your conditions (soils, moisture, low temps), and some want plants that are known to have naturally occurred in their area. Viburnum dentatum has an extremely wide range of natural occurrence (provenance); a glance at Hightshoe's text shows a distribution map shaded from Cape Cod MA down the east coast to northern FL, and along the Gulf coast to east TX. Interior areas shaded include most of those states bordering the Atlantic Ocean and Gulf of Mexico, as well as minor areas in AR, MO, TN, KY, and OH. This map is just for V. dentatum. Varietas of V. dentatum and its allies (like V. molle, V. rafinesquianum, V. recognitum, and V. bracteatum) extend this range even further. You want to know these things when selecting plants for ND, or NH, or GA. The different clones of Viburnum dentatum come from many areas; no wonder they don't all bloom at the same time! This applies not only to my garden bloom times (I have about a dozen different V. dentatum), but to the difference in WHEN they bloom for me and when they'll bloom for you. For me, arrowwoods generally bloom in May-June; for you, that may be a month or more later or earlier. The SEQUENCE of identical plants' bloom times should remain constant, though. If in KY mine proceed from Cardinal to Indian Summer to Northern Burgundy to Autumn Jazz, then you should have the same order of bloom in ND, or NH, or GA.
NEXT: One of the viburnum threads on Shrubs refers to several folks who will be again tracking bloom times in 2005, in order to help the GWers flailing about trying to match up some of their favorite fruiting plants. This will make life simpler in some respects (shouldn't be tough to have a start to finish list of all the clones' bloom times) but more confusing in others (seedlings, if not of known provenance, are going to be all over the place time-wise).
Is anyone still awake? Isn't this fun? My personal goal is to grow as many of all the viburnums as I can here in KY. Not just clones, but seedlings of known provenance too. Any that I learn to be invasive here will be eradicated, but there will still be many to permanently cultivate. These are great plants to look at, but also to learn from so that others can enjoy them successfully as well.