Charlie,

Just to be clear, you irrigate 100 trees at a time with a 1 gph emitter per tree or 100 gph flow for 12 hours or 1,200 gallons once a week. Maybe 2,400 gallons if twice a week. Am I correct? Are you giving a tree 12 gallons a week or possible 24 gallons a week. What are the type and size(age) of the trees? Is that correct? Who gave you this advice? Aloha

Most all irrigation timers today have multiple programs along with multiple start times.
you can easily have it come on for 4 hours, say at 9:00 am then repeat the cycle at 2:00, then again at 7:00 pm. the more you stretch out the cycles the better. It gives it time to absorb the water. With various combinations of separate programs and multiple start times you have endless choices to accomplish what you want to do.

Some clarification. I live in central Washington, with about 9" rain/year. Precipitation mostly comes as snow or during spring rain events. Its dry, hot and windy in the summer and cold in the winter. The trees are mostly aspens and hybrid willows (Australian willows), plus weeping willows, chokecherry, serviceberry, ninebark, and wild rose. The trees are a few years old and are about 6Â-7Â high; the bushes are smaller, perhaps 3Â high.

I have three separate drip systems, each with about 50 trees and a few bushes. Each tree has two 1gph emitters. I used to water the trees everyday for 1 1/2 hrs. So each tree receives 3 gal/day. Given the hot weather and high evaporation rates, much of the 3 gal/day water is lost. I was advised to change my watering strategy and soak the trees twice a week for about 10 hrs. This would provide each tree with 20 gals twice a week. The advice came from long term residents/farmers that have experience planting trees and gardening.

Charlie,

In very dry and high evaporation areas mulch would be critical especially wanting to make drip as efficient as possible. I agree with Homr that spreading the watering out would allow the trees to uptake more of the water. It seems to me your are losing alot of water into the ground. Trees that small would not have a root system developed to uptake 8 gallons per day. Please do some research by asking your local agriculture extension service or U of Wash what water regimen trees that tall would actually use. Just curious, were you experiencing stress from lack of water in your plants and asked local advice.? Wonder why you didn't really answer by previous question. Was I correct in my clarification summary of what you were expecting to do? If you are just interested in controllers to do what you want follow Homr's advice and break your irrigation quantity into more zones or systems or times. Are you running a commercial operation(plant nursery)? JMHO Aloha

Thanks!
The trees are for a wind break, birds, and they look really nice. I did add a 2" cover of mulch the trees, so the emitters drip on the mulch. After the helpful post from Homr, my feeling is "why didn't I think of that obvious solution. First, I will contact my local agicultural extension, or the local university about watering trees. Second, depending on their advice, I could run the drip for 3 hrs (my timers have a maximum duration of 180 min) and just repeat the cycle, as suggested by Homr. charlie

Charlie,

I would put the mulch on to of the drip line. Water on mulch and evaporating is not getting to the roots. The water soaks into the ground and is protected from evaporating by the mulch above. Also mulch because of its high undecomposed material content may resist water from penetrating and cause it to runoff to where it is not efficient for the roots to pick the water up. JMHO Aloha