Strawberries lose thier vigor? I have always heard this but not really sure how to keep a vigourous patch going. Is it the crown that does this and if you get a runner off of the crown and get it started again will the vigor return? OR do I have to order new plants? If so where do they get their plants from seed?
For future reference, as this is an interesting concept;
There is a phenomenon known as hybrid vigor or outbreeding enhancement. The technical term is heterosis and it has everything to do with genetics and selective breeding. This is a bit complex of a subject which could be described using lots and lots of big words, but here is how I understand it in a nutshell.
So whenever plants, including strawberries, have sex and produce offspring you can effectively refer to those offspring as being "hybrids" of the parents. The genetic material of the parents is shared and combined, those genes will determine what characteristics or traits the plants have. Some of these traits may be desirable and translate into stronger, more vigorous and better adapted plants (this is hybrid vigor) while others are harmful. Those that are harmful should become recessive and die out through natural selection.
However, when there is a lack of genetic diversity such as in a patch of strawberry siblings and these siblings are inbred the resulting offspring likely will not be as vigorous as the previous generation(s). As the inbreeding continues the homozygosity also increases. What that means is that the alleles of the genes (which translate into traits) are becoming more and more the same and undesirable recessive traits become more apparent making the offspring less vigorous.
While nurseries may propagate their stock of strawberries through "runners" (clones), the initial starts probably would have come from a plant started from seed. Strawberry breeders will painstakingly select parent plants with different desirable traits to crossbreed. If the resulting offspring is faster growing, produces more blossoms and bigger fruit with increased resistance do disease it is said to have hybrid vigor. Once the breeder obtains all the characteristics desired, I would imagine that this is when runners are taken as identical clones to be shipped off to the nurseries.
Here are some references: http://www.answers.com/topic/heterosis-1 http://en.wikipedia.org/wiki/Heterosis http://www.innovationaccess.ucdavis.edu/strawberry/program.htm