Watering in a greenhouse is a daily job, but I wonder about the home gardener what is the recommended routine for watering. So this is what I found. taken from http://www.weekendgardener.net/soil/wateringtips-070807.htm
HOW TO WATER PLANTS PROPERLY
It seems pretty straight forward, but one of the biggest problems gardeners have, and one of the most frequent questions they ask is, "Am I watering properly?" Because it is such a widespread problem, relax, because you're not alone, and the good news is that with a few rules of thumb, you won't have to worry about how to water ever again.
Some Bad Advice:
A lot of times gardening books will tell you that a general guideline for watering is 1 inch (2.5 cm) per week. There are a lot of problems with that guideline because it doesn't address different climates and different times of the year, and while that 1 inch (2.5 cm) may be good for a warm summer day, it may be too much for a plant on a cool spring or fall day. It also doesn't address if you get rain, or what your soil type is. More bad advice is when you're told to water, then wait for a day or two, and then dig down 2 to 6 inches (5 to 15 cm) and test the soil moisture around the root zone. Yea right, like every time you to want water you're going to dig around to check. Get real!
Some Good Advice
There are three main things you want to keep in mind:
1.The type of plants you have
Plants with deep extensive root systems, or those that are able to store moisture (like succulents), are able to survive on less water and are drought tolerant, as opposted to non drought tolerant plants that need lots of water to survive.
2.The moisture retaining capacity of your soil
Plants growing in fast draining sandy soil are going to need more frequent watering than plants grown in heavier or well mulched soil that holds water better. If you have sandy soil, you would be wise to consider mulching.
Do you live in a desert or do you get periodic rain, etc.
A Good Rule Of Thumb:
The best rule of thumb is to water as deeply and as infrequently as possible. Watering to make sure the soil is moist to at least 6 to 8 inches (15 to 20 cm) deep is best because it helps the plant grow its roots deeper into the soil. A note here: We don't mean to flood your plants! Just a good deep watering, don't get carried away. Frequent light watering in not good for your plants because it only wets the surface of the soil which encourages roots to grow upwards in search of moisture. The water evaporates quickly and the soil dries out, leaving the roots in hot, dry soil.
The Best Time Of Day
The best time of day to water is always in the morning. This gives the plant time to absorb the water and get ready to handle heat, cold, or just the energy it takes to produce chlorophyll, grow, and move nutrients around. If you water in the late afternoon or evening, the problem is that the plant is now wet and the air temperature is cool. Those are the best conditions for mildews, molds, and all kinds of disease problems. Keep life simple, water in the morning. But for many that work out of the home, this isn't possible so water when it is the best for you because the plants will be happy with the watering when ever. Till next time, this is Becky Litterer from Becky's Greenhouse, Dougherty