Xtreme Gardening CalCarb is a readily available source of carbon dioxide and calcium. Calcium is critical to the health of your plant, contributing to the strength of cell membranes and regulation of nutrient use. Calcium is known to play a major role in the quality of many crops, including tomatoes, peppers, and watermelon. Use this on all your plants for stronger healthier crops. CalCarb is a great way to supplement Calcium and CO2 directly to the foliage of your plants. CalCarb can increase plants' ability to withstand environmental stressors like heat and drought by strengthening the cell walls of the foliage. CalCarb can also assist with the production of photosynthesis as well as help prevent blossom end rot.