Excessive nitrogen
Fertilizing mature plants with high nitrogen fertilizers like ammonium nitrate (33% N) or urea (46% N) can cause fruits to split and become inedible. It is rarely necessary to add additional nutrients to well-established vegetable gardens if compost is added regularly during the year.
Plant genetics
Jalapeno pepper pods develop very superficial cracks regardless of weather conditions. The cracks usually begin to appear as the pods turn from green and black to red. The cracked tissue becomes calloused and eating quality is not affected. Many large-fruited tomato cultivars, like the beefsteak types, are prone to significant cracking. Many melons are susceptible as well. Consistent deep watering and harvesting prior to full vine ripeness will help minimize the problem.
Uneven soil moisture/dew
Longitudinal and concentric growth cracking also called "rain checking", is a common weather-related condition caused by soil moisture fluctuations, persistent rainfall, and heavy dews. Melons, cucumbers, eggplant, tomato, and pepper are often affected. When fruit skins mature and toughen they become less resilient. If the plant then takes in a relatively large amount of water the fruit skins may lack sufficient pliability and crack under internal pressure (cabbage). Water from the dew that collects on the tops of tomato and pepper fruits at the stem attachment may cause fruit skins to split into thin concentric rings. Fruits with foliage cover are more resistant to cracking and splitting because the fruits are protected from wide temperature fluctuations.
How to prevent cracking
Avoid planting in poorly drained areas of the garden. Water plants deeply and regularly through the growing season. Mulch vegetable plants with available organic materials (e.g. newspaper covered with straw, shredded leaves, grass clippings) to help maintain even levels of soil moisture. Consider harvesting fruits prior to full ripeness during periods of frequent rainfall or heavy dew.