Mythbusters: Landscape Edition

I have always enjoyed the TV show Mythbusters, where a group of people test popular myths to see if they are either busted, confirmed, or plausible. It is always interesting to see what common understandings are actually incorrect. I have decided to bust a few myths with regards to landscape issues.

"Irrigation isn't the problem, I water my grass daily"

We've all done it. It get hot, so we bump up the water for our lawn. More heat, more water. Pretty soon, we're running the irrigation two, three times a day. Initially, everything gets greener, but after a while, it stops giving us the look we want. The soil turns into a rock, the turf thins out and trees and shrubs start dying. Well, what do we do? MORE WATER?
Most don't know that stressed plants look almost the same when they are over-watered as when they are under-watered. Irrigation water carries things that rainwater doesn't. Irrigation water contains a lot more than just H2O - including two of a landscapes worst enemies - sodium and chlorine. Excess sodium can destroy soil structure and chlorine can kill microorganism communities that make landscapes healthy and self-sustaining. It is believed that the number one reason for tree and plant death on irrigated landscape is OVER-WATERING.
Part of the reason we over-water is that we largely had poor soil in the Middle Georgia area. The soil can't store water it gets from rain, so we have to give it extra. Using a soil conditioner can help re-establish the small pores in the soil.
The other part of the problem is that most irrigation systems still use "dumb" timers. These are timers that turn on and off on a fixed schedule. To get the best results for your landscape, consider a "smart" timer that adjusts watering based on real-time weather data and local soil conditions. Such systems can be a bit more pricey on the front end, but typically pay for themselves in the first year or two by reducing the water bill and cost of replacement of dead plants.
Verdict: BUSTED

"If I mow my grass shorter, I won't have to do it as often"

This is one of those times that common sense collides with science. It's common practice to cut turf grass short with the goal being to mow less frequently. It seems reasonable. If you want the grass to be 4 inches high, and you cut it to 2 inches instead of 3 inches, you'll mow half as much, right? Wrong.
Like all living things, grass has one thing it must do in order to survive as a species: reproduce. To accomplish this, many grasses have to grow to the point where they can germinate seeds. The further away the grass is from seed-bearing height, the greater it needs to grow.
Cutting grass short doesn't just make it grow quicker, it also creates other problems. When you cut grass by more than 20% of its length, it releases significant amounts of water and nutrients. This stresses the grass and exposes it to attack by pathogens. It also means you have to irrigate more often to replace the lost water.
Finally, cutting the grass short reduces the 'canopy' effect of the grass. When grass is long enough, it shelters the soil during hard rainstorms. Heavy rain falling full speed on the soil increases soil compaction, causes erosion and creates runoff problems.
Verdict: BUSTED

"If I irrigate in the evening, I'm making my water go further because its not evaporating in the afternoon heat"

It seems to be common sense: if the water isn't evaporating as fast, the plant will have a longer period to drink up the water. Watering at night, however, can encourage disease in your lawn. Although you may not see immediate effects from late watering, it will greatly increase the chances of bacterial or fungal infection.
Another issue common to our area is over-compacted, clay soils. This hinders water to get to the root zone where it can be absorbed. This further exaggerates the issue of night watering. Aerating the soil by removing 1-2 inches long soil cores from the ground rejuvenates grass by providing better access to moisture and oxygen.
The ideal time to water is first thing in the morning. It is not yet hot enough to have a major concern about evaporation, and it prepares the grass to endure the long, hot afternoon sunlight.
Verdict: BUSTED

"Landscape weed barrier fabric will keep weeds out of my planted beds"

In theory, if weeds cannot get the sunlight or space to grow, you will never have too fight them. While the thought of a weed-free yard is awfully attractive, weed barrier fabric is not a perfect solution.
I will first lay out the benefits of weed fabric. It can prevent weeds from germinating beneath the fabric by suffocation and lack of sunlight. With the lack of weeds, it will limit the use of herbicides that can be harmful to other plants. It can also help retain moisture within the soil by reducing evaporation. It can also help with erosion control in area subject to washout.
Now, the negative aspects of weed barrier fabric. My biggest complaint about weed fabric is it is far from a maintenance free solution. When you mulch over the top of the fabric, the mulch will eventually breakdown and become essentially compost. The weeds can easily germinate and grow in this layer above the fabric. In order for the weed fabric to be effective, the mulch needs to be completely removed every few mulch applications or you will simply grow weeds on top. It also reduces the ability of natural organic mulch formation from fallen leaves and other natural materials. This material would naturally biodegrade and blend with soil for a healthy soil composition. It also reduces the amount of earthworms that can get into the soil and aerate and replenish nutrients in the soil.
Verdict: PLAUSIBLE