Flowering is the process during which the pollination and fertilization of the grapevine happens. Each flower is a potential grape, as a general rule only 100 to 200 berries will make it through.
There are several environmental factors that determine when flowering will start and finish. Flowering usually starts when the mean daily temperature reaches 20 °C. Flowering can also start earlier with warmer soils (gravel) but this always depends on the grape variety. In Cyprus (dry, warm, sunny conditions), the duration of flowering can last approximately 7-10 days although in colder, wetter climates flowering might extend to 3-4 weeks.
At the start of the flowering process what is visible is something resembling a tiny grape. This is actually the calyptra which encloses all the reproductive organs. At some point the calyptra separates and exposes the anther (male part which contains the pollen) and the pistil (female part). The majority of grapevines self-pollinate which means that fertilization happens by the same vine. A very small percentage might also cross-pollinate (two different grape varieties help each other with pollination). Wind and insects do not play a significant role in pollination.
Cypriot and international grape varieties such as Xynisteri, Mavro, Shiraz and Semillon self-pollinate. Maratheftiko on the other hand finds it hard to self-pollinate. The result is what is shown in the following photograph; only a few grapes are produced of which only a handful are actually fully ripe.
Some grape growers in Cyprus plant in the same vineyard both Maratheftiko and Spourtiko for cross-pollination reasons. Both grapes flower at the same time which means Spourtiko can help Maratheftiko produce more grapes although in some locations or with some Maratheftiko clones this does not seem to work.
The following photographs were taken in our Fournia vineyard in Pano Arodes. The first photograph shows clearly that the Anther (male part) in a lot of flowers is either absent or underdeveloped. The second photograph is a comparison between our Mataro that grows in the same vineyard as our Maratheftiko. In most cases the calyptra did not separate completely; all this results in restricted pollination which leads to the production of only a small number of grapes.
In this specific Maratheftiko vineyard we have planted several Spourtiko grape vines. What we observed over the last two years was denser Maratheftiko bunches on all the vines next to the Spourtiko. This confirms the idea of cross-pollination as a possible solution. However, this does not solve the problem in all the vineyards and therefore much more research needs to be carried out in this never-ending problem.