Drip Irrigation for Montana Beds, Trees and Gardens

Why use drip instead of sprinklers for beds?

Efficiency and plant health. Colorado State University Extension's guide to drip irrigation for home gardens puts drip efficiency above 90 percent, compared with 50 to 70 percent for sprinklers, and lists the reasons: less loss to runoff, wind and evaporation, no overspray on siding or fences, and automation that suits a busy schedule. Montana State University Extension's Yard and Garden Water Management MontGuide adds that drip and soaker hoses cause minimal surface wetting while letting water reach the root zone, that soaker hoses can reduce water use by 60 percent or more, and that drip and micro-spray suit areas that dry out quickly, such as foundation plantings and borders along sidewalks and driveways.

Wind is a real factor here. The Missoula and Bitterroot valleys get afternoon wind through much of the season, and a spray head watering a narrow bed in the wind waters the sidewalk. Drip does not care.

What are the parts of a drip zone?

CSU lists the order for a permanent system as backflow preventer, control valve, filter, then pressure regulator, followed by the tubing and emitters. The backflow preventer protects your drinking water. The valve lets the controller run the zone. The filter keeps grit out of emitters, and CSU recommends 150 to 200 mesh for relatively clean municipal water and 200 mesh for in-line emitter tubing. The pressure regulator matters because CSU says drip components are designed for about 20 to 30 psi, while household pressure often runs 50 to 60 psi or more.

Downstream of that head assembly, CSU describes half-inch or three-quarter-inch polyethylene mainline, with a maximum of about 200 feet of mainline per zone. Emitters plug into the mainline or come built into emitter tubing, and quarter-inch tubing carries water to individual plants.

How many emitters does a shrub or tree need?

CSU gives practical starting points. A perennial gets two half-gallon-per-hour emitters at its base. A shrub of 1 to 5 feet, or a small tree under 15 feet at maturity, starts with two 1 gph emitters about 12 inches from the base, increasing later to 2 and then 4 gph emitters as it grows. A shrub of 5 feet or more gets three 1 gph emitters, and a medium tree of 15 to 25 feet gets four emitters about 2 feet from the trunk. For newly planted trees, CSU suggests three 2 gph emitters for a 1-inch caliper tree and three 4 gph emitters for a 2-inch caliper tree.

For larger trees, Utah State University Extension uses a formula: the area under the crown times the share of it you want wetted, divided by the area one emitter wets in your soil. USU recommends wetting at least half the root area under the drip line, preferably 60 percent or more, and its example works out to about five emitters spread evenly under a 15-foot crown in loam. USU also recommends keeping emitters above ground so they can be inspected and roots cannot grow into them. As trees grow, emitters need to move outward; a ring tight against the trunk of a mature tree misses most of its roots.

How far apart should emitters be in Montana soils?

It depends on how water spreads sideways in your soil. CSU's spacing for emitter lines is 12 inches in sand, 18 inches in loam and 24 inches in clay. Utah State gives the same pattern from the other direction: one emitter wets roughly 5 to 21 square feet in sandy soil, 21 to 65 in loam and 65 to 161 in clay.

Soils vary across western Montana's valleys, sometimes within a single lot, so it is worth knowing what is under each bed before choosing spacing. Our guide to Bitterroot Valley soil types explains how to find out what you have, and the rocky soil guide covers the cobbly ground where drip is often the only practical way to water beds.

How long should a drip zone run?

Longer and less often than people expect. CSU says that after plants are established, about one hour of run time per week is a common starting point, that sandy soils or moisture-loving plants may need watering twice a week after planting, and that native or xeric plants can be watered weekly or every couple of weeks, letting the soil dry between waterings. CSU also advises using a controller and avoiding overnight runs.

CSU's weekly water figures are a useful check: about 1 gallon a week for xeric perennials, about 2 for moderate-water perennials and annuals, 4 to 6 for a shrub from a 5-gallon container, 10 to 12 for large shrubs, and for established trees up to 10 gallons per week per inch of trunk diameter. Multiply emitters by their gph rating by run time and compare it with the target. MSU's MontGuide adds the Montana timing: woody plants need water from early spring through August, should be allowed to harden off by gradually withholding water from September to mid-November, and benefit from a deep watering after leaf fall and before the ground freezes to help prevent winter kill.

How big can a drip zone be?

CSU's limits are about 200 gallons per hour on a half-inch mainline zone (possibly more, depending on the manufacturer) and up to 480 gph on three-quarter-inch, with only 75 percent of the source flow treated as usable. Its example: fifty 2 gph emitters need 100 gph. Those numbers are why one drip zone can water an entire foundation bed. They are also why drip should never share a valve with spray heads; the run times are measured in different units. See our irrigation zone design basics for how drip zones fit into a whole system.

Is drip good for vegetable gardens?

Yes, with attention to timing. MSU's MontGuide says the cool of the evening is the best time to soak or drip irrigate a vegetable garden unless root rot is an issue, giving the soil all night to absorb the water, and recommends soaking the garden once a week to a depth of 6 to 12 inches, then waiting until the top few inches dry before watering again. MSU also notes that watering is most critical while plants are producing the edible portion, and that newly seeded plots and transplants need shallower, more frequent watering than established plants. A separate drip zone for the garden lets you change its schedule without touching the shrubs.

What maintenance does drip need?

CSU's list is short and worth following: before the first spring watering, flush the mainline, clean the filter and check the emitters; during the season, check and clean emitters periodically; and flush after any break or repair. CSU is also honest about drawbacks: leaks at ground level are hard to see, poor emitter placement can limit root growth, the system needs regular inspection, and tubing can be a trip hazard or get cut during other yard work. A bed that suddenly looks stressed in July is usually a plugged emitter, a pulled-off line or a missing end cap. Our irrigation leak signs guide covers how to spot those.

How is drip winterized in Montana?

CSU recommends removing the head assembly (portable valve, backflow device, filter and pressure regulator) and storing it indoors, and draining the mainline by uncapping it, especially where no emitter sits at the low point. CSU notes that polyethylene mainline is not damaged by freezing, but systems with many right-angle fittings may need compressed air to clear the water, and that emitters usually store fine outdoors. On permanent systems tied into a sprinkler mainline, we blow drip zones out at lower air pressure as part of the fall sprinkler blowout.

Can HJ add drip to an existing sprinkler system?

Usually, by converting a bed zone or adding a valve. We design drip zones with the filter and regulator in the right order, emitters matched to the plants and soil, and lines placed so they can be inspected. Drip pairs naturally with xeriscaping, shrubs for western Montana and watering trees in drought. This guide is part of our Montana Landscaping, Lawn & Irrigation Guide, and our irrigation systems page explains how we build. Call HJ Property Care & Tree Service at (406) 215-7319 or request a free estimate. We work across Missoula and Ravalli counties, from Missoula and Lolo to Florence, Stevensville, Corvallis, Victor, Hamilton and Darby.

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