Water excess can be catastrophic to plants

The fungus is among us, people. And I gotta tell you, it freaks me out to see all this destruction caused by over-watering in the desert.

I had a friend who moved here from the Northwest once tell me, “I don’t think you can ever water too much here.” I can’t begin to tell you how wrong this is.

We’re not used to having this much precipitation in the Grand Valley. Yes, I know 1.37 inches of rain (according to the National Weather Service) doesn’t seem like much for July in most places, but it’s a fair amount for those of us who had everything burn up last summer. In fact, it’s the 12th-wettest July since 1893.

Yes, less than two inches of rain in a month seems like a laughable amount in many other places. But here in the desert, where we’re used to keeping our landscapes alive with a lifeline of irrigation water, we have a tendency to not adjust our habits, and that causes problems.

A significant portion of the questions, house calls and samples the master gardeners are receiving at Colorado State University Extension currently are directly related to over-watering. Fungus thrives in humid, wet conditions and boy, are some of us encouraging that in our landscapes.

Here’s a typical scenario: A local homeowner brings in a sample of his lawn. Part of it is green, part is brown, and he says he’s been watering the brown spot more because he thinks it is dying from lack of water. The soil attached to the grass roots is sopping wet.

Turns out, the “extra watering” is just causing the brown spot to spread, because the wet conditions encourage the fungus that is killing the lawn. On top of that, the grass roots are so waterlogged they can’t breathe properly (yes, roots breathe) and that’s not helping matters.

Honestly, correct watering practices are the best defense to this problem. The CSU Extension recommends watering lawns between 10 p.m. and 6 a.m. to limit the amount of time the grass blades will be wet (this period of time covers the hours of the day that the grass would be wet with dew anyway). They also recommend watering to a depth of six to eight inches, which can be checked with a long-handled screwdriver. Just push the screwdriver into the ground and see if there’s much resistance, and if it goes in easily, you’ve watered enough.

CSU also recommends applying about 1 1/2 inches of water when irrigating your lawn. How do you know how long this takes? You can use empty tuna cans to measure the amount of water your sprinklers are applying to the lawn. Just let the sprinklers run for a while (they suggest 30 minutes) and see how deep the water is. Then figure out how long you should be watering.

This is where it gets a little tricky. If water is running off your lawn in the period of time it takes to apply this much water, it’s not doing much good. The clay soils we have in the Grand Valley are annoying this way — they don’t soak up the water as fast as we apply it. If this is your situation, consider cycling the sprinklers in a shorter period of time, such as 10 minutes at a time, and letting the water soak in between cycles. You still need to apply a total of 1 1/2 inches of water, but you don’t have to do it all at once.

How many times a week should you water? Well, it varies from yard to yard. It depends on how much sun or shade you have, what type of grass you have, how much you watered the last time, whether your neighbor’s watering overflowed into your yard, what the weather is like this week, etc.

I don’t have a silver bullet kind of answer for this. The truth is, every yard is different. You should watch for signs of dryness and wilt, and water your lawn when it is thirsty again.

Some signs that you should re-evaluate your watering practices are if you have brown spots in your lawn, bizarre patches of bleached-out, yellowed or brown grass, ring patterns in the grass or mushrooms popping up. Some symptoms of turfgrass fungus can appear suddenly — a matter of days or even overnight. These fungal problems have names like “dollar spot disease,” “melting-out disease,” “necrotic ring spot,” or even the nearly-impossible-to-pronounce “asochyta leaf blight.”

These can be difficult to diagnose without a microscope to get a good look at the fungus, so if you have any of these symptoms, take a sample to the master gardeners at the extension office or call them at 244-1836.

Erin McIntyre is an advanced master gardener, writer and Grand Valley native. Please email her at .(JavaScript must be enabled to view this email address) with story ideas or feedback.


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