Irrigation is quite a controversial topic in horticulture. Far too often, clients come into the office with grass struggling or detrimental fungal concerns in their gardens.  The “go to” conversation concerns the cultural practices being utilized in the landscape. Cultural controls include the homeowner’s landscaping and gardening practices. These can cover several topics, including proper fertilization, dealing with garden waste, and, of course, irrigation. While all these topics can have huge impacts on your landscape, for this article, we’ll focus on water usage.

The story of irrigation begins with the concepts of volume and frequency. Let’s take on these topics one at a time.

Volume

Volume applied, as you would think, refers to how much water you’re applying to the desired area. While there are many equations you could use to determine how much your irrigation system emits, it is much simpler to use the catch-can method.  This simply means distributing a collection device (rain gauges, tuna cans, etc.) evenly across the area covered by the irrigation head. Run that zone for a set amount of time, usually around 10-15 minutes. You’re looking for two pieces of information from this.

First, you learn how much water the irrigation head applies in a set time frame. You can use this information to adjust run times for a particular zone. Second, you’ll be able to determine whether water is being applied evenly. For instance, if ten minutes gives you 1/8 of an inch on one side and 1/32 of an inch on the opposite end of that zone, you likely need to adjust the head for better coverage.

Once you figure out how much is applied for a set period, you’ll be able to apply the optimal amount for the plants you are growing. For turfgrasses, this is ½ to ¾ of an inch per application.  For vegetable gardens, you’ll have to experiment with how much is required to wet the soil in the root zone (roughly 6 inches deep).

Frequency

Frequency is the next major concern regarding irrigation. How often you need to irrigate depends on the plants you are growing and your soil texture. As that sentence implies, plants have different water needs.

It’s important to research your broadleaf plants to understand their optimal environment. You’ll also want to familiarize yourself with the signs of water stress. Often, this is leaves that wilt in the middle of the day and do not recover when the sun goes down. Combine these signs with frequent soil checks (top ½ inch of soil dries out), and you’ll begin to develop an irrigation schedule. Keep in mind that frequency varies by season, so you’ll want year-round monitoring.

Tufgrasses

Turfgrasses are an entirely different story. They signal a need for irrigation by folding their blades, slight color changes (gray/blue), and slow rebound when stepped on. When you notice these signs on a large portion of your lawn, is it time to apply water at the rate outlined in the section on volume. You’ll want to apply the water before dawn. Early irrigation allows the turfgrass to dry out throughout the day, reducing the chance for fungal infection. Keep in mind that rain will count as irrigation. Aim for around 1 inch per week, which should translate to 1-2 times per week. Again, this will change seasonally so monitor your grasses and adjust your control heads accordingly.  For more information on watering turfgrasses, consult this document.

Soil texture is another important factor in irrigation. Soils with higher sand content will not hold water as well as soils with higher clay content. This may affect your watering schedule.

The final concern with irrigation scheduling is mixed landscapes. Your lawn spaces will not need watering as often as your planted beds. Using a single irrigation system to manage both is possible, but you’ll want to designate specific zones for lawns vs beds.  You may also consider switching irrigation heads in your planted beds to micro emitters.

Irrigation is an extremely important topic in horticulture. This article touches on the basics of operating a sprinkler system. If you’d like more information on this topic, please consult these documents. For more information on this or any horticulture topic, call your local Extension office.

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