For establishing trees and most other plants the rule of thumb is to provide the equivalent of 1" of rain a week, watering well beyond the branch spread. This requires about 5-10 gallons of water a week for very young trees- it all depends on how much area needs to be watered.

The rule of thumb is only a recipe or I should say part of a recipe, other ingredients that change the ratio are soil texture, weather temps, humidity and wind. Mulched trees lose less water to evaporation and some mulches can store water.

Ultimately, to become a knowledgeable gardener, you start with a recipe but get your hands in the soil to see how long it takes to dry out. Gradually you will learn the perfect level of moisture for the trees and other plants- that Goldilocks point of not too wet- not too dry.

Once the trees get to a decent size and are bearing fruit you will probably want to be stingy with water to improve fruit quality.

I have dry sandy soil, and I mulch for the first three years to help retain water. I water the first year after transplant only. After that they are on their own. You want the trees to build deep roots so they are self sufficient for water. I would only water after that if there are signs of water stress on the tree or an extended drought. I get 2 - 4 feet of new growth each year using these methods.

We have clay based loam here that seems to store water pretty well.

Even new trees rarely need water here as long as they're mulched.

I think one of the main reasons mulch retains so much soil moisture is that it completely shades the sun from the ground and blocks wind evaporation. In our soils, with mulch, water just sits under there until the tree uses it up.

Here in NY I plant bare root trees in my nursery and size them up with only the help of mulch- no irrigation. In general, even with mulch, timely irrigation will help things size up more quickly, even after the first year, if you suffer drought, which is common.

It is spring drought that is most dwarfing. This year my bare roots that I had sized up for a couple of years and then moved definitely suffered. Worst early spring drought in decades!

Olpea, I've read in soil text books that mulch is not as affective as people assume at stopping evaporation, in that soil itself has a similar affect. The wind and sun only works on the top couple inches, apparently.

My text books could be wrong, of course (the two I have on my shelf are 25 years old), but mulch works in many ways to retain water. It even creates it (probably not much) as it breaks down and the, uh, carbos are released from the hydrate, so to speak. I wonder if mulch doesn't also feed and increase the affect of the mychorizal fungus, augmenting that symbiosis which is known to help trees withstand drought as the hyphae increase (extend?) water access for the tree.

It's been a very very dry spring here. There was a month and a half period were we didn't get any sustantial rainfall at my location (dry from about mid March thru April). Finally, we got some rains maybe 1.5 - 2" total, but it's getting dry again.

Hman,

I hadn't considered the effect of mulch itself breaking down and producing water (much like when fuel is burned - CO2 + H2O). That makes sense.

I do think the evaporative effect is more than the textbooks infer. I'm sure you've recognized when a tree/plant is heavily mulched, the soil beneath can be very damp, where soil outside the mulched area is bone dry. I've noticed the same thing when I've put down black plastic. It stays wet (almost mud) under there for a long time.

Living ground covers can create a natural multch as well. You can use herbs like oragano or thyme that dont grow too tall in sunny spaces, and some types of say, clover or comfrey in shadier spots. THe herbs attract beneficial insects, while the clover fixes atmospheric nitrogen into the soil, and the comfrey pulls up nutrients from deep in the soil.

Yes, they use water as well, but they shade the soil, making it cooler, which means there is way less evaporation.

Mulching is good for the soil too. It protects the soil fromn the sun, but it also protects it from wind, which can dry it out, and rain, which can compact it. Certain tree leaves can put certain minerals back into the soil, creating light, fluffy "tilth", which most plants thrive in. THis "tilth" also holds water liek a sponge.

Cold front came through last night. Once again, all the storms went north of us. No rain at all.
Getting the lawn sprinklers turned on tomorrow. Bought a traveling tractor sprinkler to water my pine trees (wind break)

It has been a dry spring here in SE MI. And yet, my newly planted (March 2012) bare root orchard has not needed any water yet. 8 inches of wood chips appear to do the trick, and possibly the clay soil and the fact that I mulched the whole orchard (the entire area) help. There is no grass to draw moisture from the ground. I went there last night, sure that I had to water, and there was no need. I don't even have to worry about dwarf versus semi-dwarf, it is still so moist under there. The few uncovered patches were dry.

I use clover in my lawn in order to actually grow grass, that is how sandy my soil is. Without clover, the grass dies, and all that's left is sand dunes. The clover helps retain moisture, and appears to add nitrogen far beyond it's boundaries.

As far as mulch, I mix grass/clover clippings with wood chips created by my chipper, let it all compost some and it makes a perfect mulch, that usually breaks down by the next year. There is a huge difference in moisture and temperature under the mulch then in the surrounding sand soil. This appears to be enough, and after a few years, the soil around the tree becomes very rich, holds water, and I don't even need to mulch any more.