Gardening and Horticulture - Watering trees

I would like to know how much water the following 15 gallon sized trees need (watering once a week):

Haas Avocado
Maple
Dwarf Orange, Lemon, Lime and Nectarine

Thanks.

(Southern California)

Hass Avocado: When watering, it is best to soak the soil well, then allow it to dry out somewhat before watering again. Depending on the weather, your tree may need more water. Typically, trees need to be watered two to three times a week. At planting a tree can take 2 gallons of water a day. A mature tree will take about 20 gallons of water a day.

Maple: Some species are more drought tolerant than other. Red maple prefers moist conditions. A rule of thumb for watering trees is to water one hour per inch diameter of the tree. Place the hose at or beyond the drip line for the most effective watering.

Citrus trees: Young trees should not be allowed to dry out. The frequency of watering will vary with soil type and seasonal conditions (as with all trees), but it is likely to be at least weekly while the trees are being established. Moisture should be monitored due to small root system. Usually frequent watering of short duration is required. Mulching reduces surface evaporation around young trees of any kind. Mulching also keeps soil cooler, which is important while trees are getting established.

I know that for mature Haas trees in our part of southern California, 250 - 300 gallons a week (once a week) is what is generally recommended. Haas should only be watered deeply when mature - not superficial waterings. What I am trying to determine is for younger trees (like our 15G) and how many gallons how frequently. Since, our nozzles that were installed are adjustible, my best guess based on the type of nozzle is that it is getting about .5G/minute. So, I currently have it set for 20 minutes - twice a week. The same nozzle and line is on the maples and citrus trees. I just wanted to make sure this was OK or if I should add more time or one more watering. It's going to be averaging around 90 degrees daily here soon. Thanks.

Contact your local Dept. of Agriculture Extension Agent for watering schedules for trees in your area.