The lone voice of horticultural reason

“Installing an automatic drip or overhead irrigation system for shrubs, trees or perennials mean you never have to water them by hand”

Blessing or curse? Shrub irrigation systems are both.

Wrong – and I’ll take some of the blame here. On the site I’ve written about installing drip line irrigation around plants in the landscape, even shown how to do it, but perhaps was not clear enough about one crucial point: You’ll still need to monitor the amount of water being delivered to the various plants, and no doubt water some of them by hand.

Drip line and overhead irrigation systems installed around trees, shrubs and perennials are a tricky enterprise, filled with mystery and witchcraft. It’s nearly impossible to design and install the system, either by yourself or with the aid of an irrigation company, so that it waters everything perfectly.

Particularly the first season. First year in the ground, plants require more water than these systems are going to deliver. Sure, you should set the system (if automatic) so that it runs longer the first season than it will in the second and third, but this is always dicey. Drip line systems – I recommend using Rainbird drip line hose, with 12” emitter hole spacing – can be circled two or three times around a new evergreen tree, once around each of those shrubs over there, and woven through a perennial planting, in an attempt to provide different amounts of water based on the size and type of plant, but it’s always a crapshoot.

Plus I should note the lesser potential of running a landscape plant irrigation system too long or too often, such that a perennial or a finicky young evergreen shrub receives too much water, and dies, while the young birch tree or six-foot pine down the line is as happy as a clam. This is gardening, after all. You want an easy hobby, collect state quarters.

After first-year monitoring, supplemental hand watering as needed, and probably adjustment to the system (either in time duration or addition of drip line), irrigation systems can do a decent job of watering landscape plants in their second season and beyond. You’ll get the hang of how long to run the system, and how often, based on natural rainfall, temperatures, drought, extreme heat of midsummer, etc.Bottom line: An automatic irrigation system for landscape plants is hardly a set-and-forget exercise. Once installed, you need to monitor the plants at least weekly the first season. Eyeball their health – deciduous shrubs and perennials will tell you in just a few weeks if they’re not happy. Evergreens will lie, appearing proud and stout for an entire season, before showing up dead in spring. Not enough water the first year, or in supplemental years. Check the line at least three times per month, dig away mulch here and there along the line, including the end of the line(s), to see that water is dripping from the emitter holes when it’s turned on.

From my experience, however, the only sure way to properly water your landscape is to nix all thought of an irrigation system, and water all plants by hand, with a watering wand.

How much water? You take a five-gallon bucket, turn your hose on full bore, and time how long it takes to fill the bucket with a watering wand attachment (thirty seconds, maybe?). You then water the newly planted trees for 90 seconds every three days (the first spring and summer in the ground), the small to medium size shrubs for twenty seconds every three days, each perennial for six seconds every five days (all depending on sunlight exposure and soil drainage), and you know the new ball-and-burlap trees are getting 15 gallons of water, the shrubs around four gallons, while the perennials are receiving a gallon. Welcome to gardening.

One other point, don’t let an irrigation company propose an above ground, spray irrigation system for trees, shrubs and perennials. They’ll want to install vertical pipes in the landscape, with water spray heads – think of a lawn irrigation system on steroids – that waters your plants with an overhead spray. No. The plant foliage blocks the water from getting around the base of each plant, and constant overhead watering encourages fungal disease and mold growth.

If yours is not a large collection of landscape plants, water your plants by hand. You’ll have much better success. If you decide to try an irrigation system for landscape plants, use only a drip line system, installed on the ground, circling or weaving around each plant, covered by organic mulch. Don’t bury the lines underground, then cover with mulch. Makes it darn near impossible to locate the spot where a squirrel gnawed a hole in it after three years, rendering the entire system useless until repaired.

Don Engebretson
The Renegade Gardener