Q. The landscape people are into variable drip emitters and think I am a little looney sticking to drip emitters.  How do you determine how many gallons to give large trees like African sumac, bottle trees, Swan Hill olives, Yew pines and chaste trees? A. No one puts it in gallons because there are too many different manufacturers and rates of deliveries of different irrigation emitters and sprinklers. These can vary from 1/4 gallon per hour (1 liter) to five gallons per hour. Then there are the types that are variable and can be twisted open to give you more or fewer gallons per hour. Drip emitters color coded for gallonage You have to figure make the conversion and convert it yourself. It is not terribly hard to do, particularly in drip irrigation. Each emitter is labeled or color coded to the gallons per hour that they emit. The hardest emitters to figure out are the types that can be adjusted (variable) to different amounts of water. Many of these are adjustable between 0 (shut off) to 10 gallons per hou It seems simple. You just twist the emitter open and it delivers more gallons per hour. But in actuality it begins to defeat the purpose of drip emitters: precision. Also many of these variable flow emitters are not pressure compensated. If it is not pressure compensated, then opening one emitter and allowing more gallons to flow can affect the number of gallons on all the other non pressure compensated emitters on the same line. Variable drip emitter This can mean you have to twist open or twist close each emitter along the same line perhaps multiple times to get the flow that seems to be appropriate. Not only that but these variable output emitters frequently emit so much water so quickly at the higher settings that it results in water puddling and running off to low spots. This is exactly contrary to the reason we should use drip emitters. With many different types and sizes of plants along the same line the next difficulty for most people is to figure out what size (gallons per hour) to match up with each plant along the line. So this is how I do that. The first thing I do with an emitter line attached to a single valve is determine how many hours or minutes the valve will be left open for watering. Frequently for drip irrigation the shortest time is one hour. Flag emitters easy to clean and color coded “Yikes” you might say because most people want to irrigate fifteen or twenty minutes. The problem with these short irrigation times is that it may force you to use the variable output emitters. Or it results in water applied so rapidly it does not penetrate the ground and instead runs and puddles somewhere else. Start with a minimum of one hour. In some cases you might water for two or three hours on a single line. What difference does it make? You are not standing there with a hose and it can take all night if you want it to. There is no problem watering at night with drip irrigation. Let it soak long, slowly and deeply. Try to use at least two emitters per plant in case one plugs. Here is the one hour example. One gallon plants, give them one gallon per hour (two, half gallon per hour emitters). Five gallon plants give them three to five gallons per hour (two, two gallon per hour emitters or three, one gallon per hour emitters). Fifteen gallon plants give them 8 to 15 gallons per hour (two, four gallon per hour emitters or two, five gallon per hour emitters or three, three gallon per hour emitters, etc.) Distribute the emitters under the plant canopy, one foot from the plant with distribution tubing and secure them in place with rock mulch or stakes to hold them in place. Emitters should be above the mulch so you can check them for plugging. Plants that are spaced closely together can and will get water from each other. Does this help a bit?