Best Time to Water Plants in the Vegetable Garden
The answer to when to water plants in the vegetable garden actually has two answers.
Watering Plants in the Morning
The very best time to water plants is in the early morning, while it is still cool. This will allow the water to run down into the soil and reach the roots of the plant without too much excess water lost to evaporation.
Watering in the early morning will also make the water available to the plants throughout the day so that the plants will be able to deal better with the heat of the sun.
There is a gardening myth that watering in the morning will make the plants susceptible to scorch. This is not true. First of all, almost all areas in the world do not get intense enough sun for water droplets to scorch the plants. Second of all, even if you live in an area where the sun is that intense, the water droplets would be evaporated in the heat long before they could focus the sunlight.
Watering Plants in the Afternoon
Sometimes, due to work and life schedules, it can be difficult to water the garden in the early morning. The second best time to water a vegetable garden is in the late afternoon or early evening.
If you are watering vegetables in late afternoon, the heat of the day should have mostly passed, but there should still be enough sun left to dry the plants a bit before night falls.
Watering plants in the late afternoon or early evening also cuts down on evaporation and allows the plants several hours without sun to take up water into their system.
One things to be careful of if you water in the late afternoon is to make sure that the leaves have a little time to dry before night comes. This is because damp leaves at night encourage fungus problems, such as powdery mildew or sooty mold, which can harm your vegetable plants.
If you are using a drip or soaker irrigation system, you can water right up until nightfall, as the leaves of the plant do not get wet with this form of watering.
[Source - gardeningknowhow]