Q. I have a LOT of different shrubs and trees on only 2 valves (front & back). The shrubs have 2 emitters per shrub and range from 2- 2gph for plants like photinia, red autumn sage, fountain grass, jasmine vines, rhaphiolepsis etc.; and  2-4gph on euonymus, abelias, boxwood, honeysuckle vines etc. The trees have more emitters. My landscaper told me to water 6 days per week for 2-20 minutes per day (equals 4 hours per week). Star nursery advised me to water only 3 times per week for 45 minutes per day. Plant World advised 6 days per week. So, what to do?             My biggest problem is my 8 year old magnolia tree, trunk diameter about 5″, has 4-4gph emitters. It used to be very full, now it’s about 10 ‘ high & the leaves are dark brown, dry and falling off.  All help would be appreciated. A. You even confused me. In their defense I would have to say it’s possible that all three could be right. Because plants are adaptable to different situations there can be several right answers to one irrigation question. Nurseries are there to provide service, the best answers they can muster up. I am an educator so let me take a stab at it from an educator’s point of view. I would like to give you enough information so you can solve your own problem with irrigation. But you I think already realize that this is not the best irrigation setup for conserving water. You will have considerable waste even though it is on drip irrigation just because you have so few valves. Bear with me on this. Let’s all agree for the most part that as plants get larger they will require more water. Let’s also agree that large plants will use more water, and considerably more water, is one smaller plant. The larger the plant, the more water it should receive. Irrigation valves are basically an on and off switch for water; when the valve is open, water flows. When the valve is closed, water stops flowing. Since you have one valve in the front and one valve in the back, these switches open water to all of your plants in the front at the same time and the valve in the back does the same for plants in the back. There are three basic questions that must be answered; 1) how long to water, 2) how much should be applied, and 3) when to apply it. The valves basically solve the question when to water. The drip emitters solve the question about how much to water. Irrigation clock answers the question when to water. The irrigation valves allow water to flow and the emitters determine the amount of water applied to each plant. The length of time the valve is open combined with the size of the emitter determine the amount of water delivered plant. This is where the confusion begins. To make it as easy as possible to irrigate let’s hold one of these variables constant. Arbitrarily, let’s hold the length of time the irrigation valve is open to one hour. Just for the sake of argument. It could be 30 minutes, it could be 90 minutes, but let’s just hold it at 60 minutes. If we make this decision first, how many minutes to open the valves, it can make our other decisions much simpler. So we now agree the valve will be open for 60 minutes for drip emitters. This is how I typically determine an irrigation schedule for drip. To determine how much water each plant will get we have to size our drip emitters. Because of plugging, it can be a little bit dangerous to give plants only one emitter. If that’s emitter plugs, chances are we will lose the plant in a short period of time during the summer. To determine how much water to give the plant at each watering or when the valve is on we look at its size. The smaller plants of course require less every time the valve is on. So for the sake of argument let’s do this. Let’s give a plant 1 gallon of water every time the valve is open (in this case one hour) for every foot of its mature size. A very small plant may get 1 to 2 gallons. A medium-sized plant may get 3 to 6 gallons. A large shrub may get 8 to 15 gallon every time it’s watered. The larger the plant, the more emitters it will need under its canopy. A very small plant may require one to two emitters. A medium sized plant might require 3 to 4 emitters. A large shrub might require 6 to 8 emitters. So now you will take the number of gallons you are giving this plant and divide it by the number of emitters you will provide for each plant. When you do this, you will determine the number and size of the emitters you will give to each plant. So for instance a medium sized plant may get 3 to 6 gallons at each watering delivered by 3 to 4 emitters. So the size of the emitters might be 1 to 2 gallons per hour. But I would keep all the emitters going to one plant at the same size. So what if it’s one or 2 gallons more than you calculated. What is important is that you apply enough water during one irrigation to water the entire rootzone of each plant (plus a little extra to keep those salts in our city water flushed out of the rootzone). So now we have answered two of the questions; how long to run the valve and as a result of that how much water each plant will get because you have selected the correct size and number of emitters. The next and last question is probably the most difficult to answer. Remember, you have elected to set the time that the