I finally own my home and this is my first spring. I have a decent front lawn that I want to keep as green as possible. I've always been told not to water in the day as it can burn the grass (as a result of the sun). Is this true? Is it true all the time? It's a nice 75 degress out right now, will this hurt my grass if I water it now? What about when it's a hot 95?
Any insight or recommendations?
Burning is open to debate (search this site for examples) but is probably more of an issue for delicate plants and buds, rather than tougher plants.
The big issue about daytime watering is that of evaporation. Here in Texas you will waste a large percentage of the water (especially if spraying) and it is against bylaws in summer in most cities.
In cooler climates, night time watering is thought to encourage to mould and rot. I don't ever recall this being an issue with lawns when I lived in the UK (where it rains at night!)
Lawns should be watered between the hours of 2am and 9am (or thereabouts). Evaporative loss is a concern for two reasons: it's a waste of water, and when a significant proportion of the water you apply evaporates, your turf isn't receiving as much water as you think it is. But even if you account for this evaporative loss (and you should) and don't care about wasting water (you should care), it is still important to limit your watering at a time that doesn't extend the amount of time your turf is wet (from dew, for example). If you water at 8pm, you are extending that wet time by 6 hours or more. Diseases, especially fungal infections love wet turf, and the longer the grass is wet, the greater the chance of infection. By 4am, your turf is already wet with dew, and it will dry out once the sun comes out again.
Just as important as the question of when to water is how much and how frequently to water. Water as infrequently as possible while still providing the proper amount (here is a nice guide, though every state will have one: http://pubs.ext.vt.edu/430/430-010/430-010.html). A typical lawn needs (depending on soil, location, grass type, slope, etc.) between .75" - 1.5" of water a week (including rainfall). The only way to know how long to water is to know how much water your sprinkler applies in a given time (see How to Calibrate Sprinkler Heads - http://edis.ifas.ufl.edu/pdffiles/LH/LH02600.pdf). Only after you know this can you determine how long you need to let those run.
Congratulations on the purchase of your house! Lawn care can be one of the most complicated things for new homeowners and there is definitely a right and wrong way to water your lawn. Things like seasons, how much water to use and how often to water your lawn all play a big part in the health of your lawn.
We have an article on watering lawns that has instructions and tips to maintaining a good lawn. In brief:
Water a Lawn Deeply and Infrequently
Deep watering (about one inch of water, one or two times a week) is much better for your plants than shallow, frequent watering, which leads to shallow roots and impacts the ability of your lawn to survive drought conditions.
Change the watering schedule according to the seasons
Grass does not need the same amount of water when it is growing as it does when it is dormant. So change your watering schedule depending on the season and how much rain you get.
Do not overwater
Watering too much is a waste because once the soil is saturated, excess water will drain off into the ground water system. If a soil remains saturated, lawns can suffer from lack of oxygen, which is equally as bad as suffering from drought.
Watering in the day is actually good for the plant because it reduces the chance of it getting mold/disease. However due to higher evaporation rate in the sunlight/day it is best to o it at night when the humidity/temp/light is lower to reduce your water use and also to let the water soak to a deeper level that just the top 1 inch.
