More vigorous varieties tend to shade spur leaves in spring with rapidly growing shoots that send all their energy forward. I've come to believe that this has a strong influence on whether spurs can provide enough energy to develop fruit. Lacking adequate energy they abort. When conditions are cloudy shortly after flowering, the issue is exacerbated. Inadequate light on spur leaves also is probably a strong contributor to biennial bearing- second to excessive cropping, of course. It is in the days immediately after petal fall where the issue is crucial- the total period being about a month. I believe it may be useful to eliminate some of the most vigorous new wood- especially water spouts, as soon as they appear, in order to keep spur leaves sundrenched at this crucial time. This is my own idea and only loosely connected to research based information, but it is at least a logical leap from what we do know. We know the growing shoots don't supply the fruit with energy until they've stopped growing in mid-summer. We also know that they shade the spur leaves and make them less able to harvest light and convert it to energy. And finally, we know that the crucial period for spur leaves to hold fruit and develop flowers for the following year is in the 3-4 weeks post petal fall. My conclusion appears to be obvious. I'm not saying this is the only other issue in play here, and various varieties probably hold or abort fruit for other reasons that are more complicated.

I have seen them too. Mixed messages concerning hardiness and whether the plants are really perenial. No information whether the seeds germinated 'normally' or developed in a laboratory. They are marketed as Rudbeckias: Berlin, Dublin, Peking.

Kinda. Cultivars of avocados have two different kinds of flowers, usually called simply "A flowers" and "B flowers". Some cultivars have only "A flowers" and some have only "B flowers". "A flowers" are receptive to pollen in the morning and shed pollen the following afternoon while... "B flowers" are receptive to pollen in the afternoon, and shed pollen the following morning. Consequently from a technical standpoint, production is best with cross-pollination between two cultivars, one with type A flowers and one with type B flowers. But the reality is, most cultivars of avocado seem to get better and better at producing furits as they get older, another pollinator or not. And if you live in a good avocado growing climate, there's almost invariably another avocado tree in the neighborhood that will be your avocado tree's buddy in the next many years. By the way, 'Hass' has A flowers. And most trees in 5-gallon cans or larger will prodcue a few fruit the following year. Joe

Open pollinated plants are pollinated in two ways, either cross pollination between two plants by wind, insects, or water. Or self-pollination by mail and female flower parts contained on the same plant. Hybrid seeds are a result of cross pollination between two different varieties of the same plant.