What if fruit walls were invented/discovered earlier?


Fruit Walls

The design of the modern greenhouse is strikingly different from its origins in the middle ages
[*]. Initially, the quest to produce warm-loving crops in temperate regions (and to extend the growing season of local crops) didn't involve any glass at all. In 1561, Swiss botanist Conrad Gessner described the effect of sun-heated walls on the ripening of figs and currants, which mature faster than when they are planted further from the wall. Gessner's observation led to the emergence of the "fruit wall" in Northwestern Europe. By planting fruit trees close to a specially built wall with high thermal mass and southern exposure, a microclimate is created that allows the cultivation of Mediterranean fruits in temperate climates, such as those of Northern France, England, Belgium and the Netherlands.

An English fruit wall. Wikipedia Commons.

The fruit wall reflects sunlight during the day, improving growing conditions. It also absorbs solar heat, which is slowly released during the night, preventing frost damage. Consequently, a warmer microclimate is created on the southern side of the wall for 24 hours per day. Fruit walls also protect crops from cold, northern winds. Protruding roof tiles or wooden canopies often shielded the fruit trees from rain, hail and bird droppings. Sometimes, mats could be suspended from the walls in case of bad weather.
The fruit wall appears around the start of the so-called Little Ice Age, a period of exceptional cold in Europe that lasted from about 1550 to 1850. The French quickly started to refine the technology by pruning the branches of fruit trees in such ways that they could be attached to a wooden frame on the wall. This practice, which is known as "espalier", allowed them to optimize the use of available space and to further improve upon the growth conditions. The fruit trees were placed some distance from the wall to give sufficient space for the roots underground and to provide for good air ciculation and pest control above ground.


Source: http://www.lowtechmagazine.com/2015/12/fruit-walls-urban-farming.html
 
How much earlier, because there wouldn't have been a need for them during the Medeval warm period, there were wine grape growing in England during that period. Perhaps it is invented in Scandinavia or elsewhere in the north and spreads south as the climate cools. Either way it isn't going to give a massive boost to productivity like the agricultural revolution did in Britain from the 1700s.
 
They will probably only be invented/discovered, as in OTL, in a cooling climate phase, where the crop is already established in the region. A fruit wall allows the yield to be maintained so that the same crop can still be grown rather than extending it's range.

Are there any other local historic cooling periods where that could have happened?
 
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