I gave the pumpkin plants some Lithovit (AKA CO2) this afternoon and then some calcium nitrate this evening. Lithovit is the product name for a calcium product that helps the plant deal with heat stress and photosynthesis. Sprayed finely onto the leaf surface, the nano sized particles are taken up directly through the stomata and converted into carbon dioxide. By doing so Lithovit can considerably increase the photosynthesis rate, since the essential factor limiting photosynthesis outdoors is the natural CO2 content of the air. This leads to yield increases, accompanied by a reduced water requirement, with Lithovit the plants are able to keep the stomata closed longer in case of water stress. In addition, the micronutrients also contained in the product and the trace elements that influence plant physiology, such as manganese, copper, zinc etc. increase the resistance, growth of the pumpkin plant and hopefully the pumpkin. Lithovit is 100% organic calcite carbonate from natural limestone deposits.
I would prefer not to use calcium nitrate on my pumpkin plants because it is a chemical fertilizer but because of high potassium levels in my soil I am concerned about calcium uptake so I will probably do 2-3 foliar applications on calcium nitrate this season.
I've read a lot about the importance of calcium uptake and movement through the vascular system of the pumpkin plant this off season and I'm convinced that calcium being transported to the pumpkin is critical in fruit set and the pumpkin going heavy so I'm doing what I can to make sure that the plant is getting the calcium that it needs. Hopefully by doing and additional watering I can solve or reduce the issues I had last year with the pumpkins going very light.
If you would like to try the products mentioned try my Giant Pumpkin Growing Kit.