Most fruiting vegetables require successful pollination for fruit development. Some are self-pollinated while others are aided by wind or insects. Self-pollinated crops are those where flowers are designed so that the pollen pollinates the flower that produced it. Some legume crops have this system and in some cases pollination occurs before the flowers even open. Other pollination systems are more open (cross or open-pollinated) and even though pollen from the same flower can successfully pollinate the flower, pollen from other flowers on the same plant, or plants of the same species, can be carried between flowers by wind or insects.
Cross-pollinated systems can have male and female flower parts in the same flower (perfect flowers) or they can have separate male and female flowers on the same plant, or plants can have all male or all female flowers. These systems are designed for the freer exchange of genetic material between plants of the same species. Common vegetables having separate male and female flowers on the same plant are cucumbers, squash, pumpkins and other cucurbits and sweet corn. Asparagus is a good example of a vegetable where each plant has either all male or all female flowers.
Pollen designed to be carried by insects is generally large and heavy, while pollen carried by wind is light and may even have “wings” to help it be caught and carried greater distances. Wind-pollinated crops also produce huge amounts of pollen (think pine trees here). Flowers that are aided by insect pollination will benefit from having bee hives brought into the field during the flowering phase.
Robert Westfield wrote a good review article on vegetable crop pollination titled “Pollination of Vegetable Crops.” The article has a table, which I’ve included below, on the general times required from flowering to harvestable fruit. These time periods are only general and can be affected by temperature and other climate conditions, but it does give a general timeframe that some will find helpful.
Source: MSUE