Science News: Watering fields in California boosts rainfall in Southwest

"What we do with water management really has an impact on climate — locally, regionally and globally.”

Irrigation has downstream effects on climate and runoff to Colorado River

BY ERIN WAYMAN 10:06PM, JANUARY 22, 2013

Magazine issue: Vol. 183 #4, February 23, 2013, p. 16

Farmers in California help make it rain in the American Southwest, a new computer simulation suggests. Water that evaporates from irrigated fields in California’s Central Valley travels to the Four Corners region, where it boosts summer rain and increases runoff to the Colorado River, researchers report online January 12 in Geophysical Research Letters.

This climate link may be crucial to the 40 million people who depend on the Colorado River for drinking water. That number could nearly double in the next 50 years at the same time that droughts are projected to become more common in the Southwest. Since the Central Valley’s supply of irrigation water faces an uncertain future, it’s important to examine how shortfalls in California might affect climate change in the region, says study coauthor Jay Famiglietti, a hydrologist at the University of California, Irvine.

“We have to understand these connections better to deal with changes in water availability,” he says.

The Central Valley is one of the world’s most productive agricultural regions. More than 50,000 square kilometers of the valley are irrigated, equaling one-sixth of all irrigated land in the United States.

A study in 2011 showed that watering the area’s crops cools local temperatures and increases humidity. But the work didn’t find any larger climate ties outside the region, because it relied on a regional climate simulation, which has trouble estimating conditions along the boundaries of a study area, Famiglietti says.

To overcome this problem, Famiglietti and Min-Hui Lo, now at the National Taiwan University in Taipei, simulated global climate over a 90-year period. They added in 350 millimeters of water — coming from groundwater and surface reservoirs — to the Central Valley between May and October each year. The researchers say that’s a realistic amount of irrigation based on published agriculture and climate data.

The simulations revealed that evaporation doubles in the Central Valley when there’s irrigation. That water vapor circulates to the Southwest during the summer monsoon season, which naturally brings rain to the area. “The monsoon is like a big campfire burning away over the Southwest,” Famiglietti says. “The irrigation acts as fuel on the fire.” In addition to bringing more water to the atmosphere, the water vapor brings more energy. And it changes the regional circulation, drawing in even more water vapor from the Gulf of Mexico.

Together, these changes intensify the monsoon season, resulting in a 15 percent increase in rainfall in Utah, Colorado, New Mexico and Arizona and a 28 percent increase in runoff to the Colorado River compared with simulations lacking irrigation. Some of the water returns to California via the All-American Canal, which brings water from the Colorado River to Southern California, the simulation suggests.

“It’s a nice first step,” says hydrologist Michael Puma of Columbia University. “And it’s a link that we need to investigate quite a bit more.” Many other variables, such as sea surface temperatures, also influence climate in the Southwest. To better estimate the strength of irrigation’s effect in the real world, more complex simulations that take these other factors into account are needed, Puma says.

The study also highlights the importance of investigating irrigation’s role in climate in other parts of the world, as well as other ways in which people’s use of water might have unintended consequences, Famiglietti says.“What we do with water management really has an impact on climate — locally, regionally and globally.”

https://www.sciencenews.org/article/watering-fields-california-boosts-rainfall-southwest

Citations:

M-H. Lo and J.S. Famiglietti. Irrigation in California’s Central Valley Strengthens the Southwestern U.S. Water Cycle. Geophysical Research Letters. Published online January 12, 2013. doi:10.1002/grl.50108. [Go to]

S. Sorooshian et al. How significant is the impact of irrigation on the local hydroclimate in California’s Central Valley? Comparison of model results with ground and remote-sensing data. Journal of Geophysical Research-Atmospheres. Vol. 116, March 16, 2011, D06102. doi: 10.1029/2010JD014775. [Go to]

Further Reading:

S. Perkins. Crop irrigation could be cooling Midwest. Science News. Vol. 177, February 13, 2010, p. 15 [Go to]

S. Perkins. Going down: climate change, water use threaten Lake Mead. Science News. Vol. 173, February 23, 2008, p. 115. [Go to]

S. Perkins. Hey, it’s cooler near the sprinklers. Science News. Vol. 171, March 17, 2007, p. 174. [Go to]

This article is reprinted as fair use in education, as one cannot directly access whole Science News articles unless one subscribes to Science News.

Science News: Crop irrigation could be cooling Midwest

“A variety of climate simulations don’t show such long-term changes in precipitation, probably because those simulations don’t take irrigation into account, Robock and his colleagues say. July, Robock noted, is when irrigation on the Great Plains is most profligate, with more than one-third of groundwater withdrawal occurring during that month.”

Drop in hot days blamed on moisture from Great Plains

BY SID PERKINS 2:02PM, JANUARY 22, 2010

Magazine issue: Vol. 177 #4, February 13, 2010, p. 15

ATLANTA — If summers seem cooler and wetter in parts of the Midwest in recent years, you can thank — or blame — farmers, two new studies contend.

While average global temperatures rose about 0.74 degrees Celsius during the past century, the U.S. Midwest has experienced a noticeable slump in summer temperatures in recent decades, reported David Changnon, a climatologist at Northern Illinois University in DeKalb, on January 19 at the annual meeting of the American Meteorological Society.

On average, daily high temperatures in Chicago rise above 90° Fahrenheit (32.2° Celsius) on 24 days each summer. But from 2000 through 2009, only two years tallied more than 24 days hotter than 90°— the lowest decadal total in 80 years, Changnon noted.

Rather than being just a statistical anomaly, the recent cool temperatures seem to be part of a steady long-term decline in summertime highs in Chicago, Changnon and his colleagues found. The last 10 years have seen a total of only 172 days above 90°; the 1930s saw more than twice as many. And Chicago wasn’t alone. The team noted a comparable decline in unusually hot days at 13 other sites in a swath stretching from western Iowa through Illinois to eastern Indiana.

From 1970 through 2009, average high temperatures at the sites in Iowa and Illinois during July and August were between 0.5 and 1.0 degrees F (0.28 and 0.56 degrees C) cooler than they were for the years 1930 through 1969, the researchers found. The amount of precipitation received in the region has changed substantially as well: Average rainfall for July and August from the 1970s through 2009 was about 0.33 inches (0.8 centimeters) higher each month than it was from the 1930s through the 1960s.

Changnon suggested that fewer hot days and more precipitation are linked, because humid air warms more slowly than dry air does. One likely source of the extra moisture is the region’s agriculture. Plants pump vast amounts of water from surface soil into the atmosphere as they grow, and thirsty row crops such as corn and soybeans are much more prevalent in the region these days — about 97 percent of farmland is planted in those crops now, versus about 57 percent in the 1930s, Changnon notes. Also, the plants are spaced more closely now (about 30 inches apart, versus the 40-inch spacing typical in the 1930s), a trend that has boosted the numbers of water-pumping plants per acre by about 60 percent.

Even if much of the extra summer rainfall in the Midwest derives from water in local soils, the original source of that moisture might be an irrigation spigot somewhere on the Great Plains. A rapid rise in irrigation in that region apparently has boosted precipitation downwind in the Midwest, Alan Robock, an atmospheric scientist at Rutgers University in New Brunswick, N.J., reported January 21 at the meeting. Rather than running off into rivers and streams or soaking back into the ground, Robock added, most of that liberated groundwater was used by plants, evaporated into the air and was carried downwind, where it condensed in clouds and then fell to the ground as rain.

In 1930, in a swath of plains that stretches from South Dakota down to Oklahoma and the Texas panhandle, farmers irrigated only about 7,500 square kilometers, an area about half the size of Connecticut. But by 1980, he notes, irrigated farmland in this same area covered about 60,000 square kilometers. During the 20th century, irrigation pulled more than 333 cubic kilometers of groundwater from aquifers beneath the Great Plains.

When Robock and his colleagues analyzed precipitation at more than 300 weather stations from central Wisconsin and Michigan down to northeastern Arkansas and northwestern Tennessee — a region that includes much of the same area studied by Changnon and his team — they too found that rainfall had increased. At sites in that swath, precipitation during a typical July late in the 20th century was between 25 and 50 percent higher that it was early in the century.

A variety of climate simulations don’t show such long-term changes in precipitation, probably because those simulations don’t take irrigation into account, Robock and his colleagues say. July, Robock noted, is when irrigation on the Great Plains is most profligate, with more than one-third of groundwater withdrawal occurring during that month.

Future analyses will compare the results of simulations that include irrigation with those that don’t, Robock said. Results of those studies might allow the team to more confidently pin the blame for the region’s increased July rainfall on Great Plains irrigation, he noted.

https://www.sciencenews.org/article/crop-irrigation-could-be-cooling-midwest

(Reader’s note: “Blame?”  Rain and milder summer weather than 90 degrees is a good thing!)

Citations:

Changnon, D., V. Gensini, and J. Prell. 2010. A common Midwestern question: Where have all our 90° F days gone? American Meteorological Society meeting. Jan. 17–21. Atlanta. Abstract available: [Go to]

DeAngelis, A. . . . A. Robock, et al. A. 2010. Great Plains irrigation produces enhanced summer precipitation in the Midwest. American Meteorological Society meeting. Jan. 17–21. Atlanta. Abstract available: [Go to]

Further Reading:

Perkins, S. 2007. Hey, it’s cooler near the sprinklers. Science News 171(March 17):174. Available to subscribers: [Go to]

This article is reprinted for fair use in education, as one cannot directly access whole Science News articles unless one subscribes to ScienceNews.

A conspiracy for Planet Money: saving water

A residential property in Grants Pass.

Planet Money, you asked for conspiracy theories.  Mine is about the environmental fad of saving water, regardless of local conditions, supplies, or needs.  This started in the ‘80s, with people telling us that only 2% of the water on Earth is fresh, and we must therefore conserve it, that it is a precious resource.  It is not precious, it is vital to life and healthy living, and now it is overpriced by the unit in many, if not most, places in this country and around the world. 

Governments in the United States and throughout the world have taken it upon themselves to ration water by price, instituting low base rates and high unit prices, the opposite of previous water pricing, which was all base rate.  

California cities have led the way, with tiered pricing, charging more per unit for higher tiers of use, the opposite of normal business pricing. http://www.nytimes.com/2014/05/09/us/a-thirsty-california-puts-a-premium-on-excess-water-use.html?_r=0   

That practice has spread to Oregon, including my city of Grants Pass, encouraged by state officials.  High unit rates have spread to sewer rates, with units based on winter water use, putting downward pressure on household water use.   My sewer bill jumped from $20 to $40 when these unit rates were instituted, and this year it jumped to $75, because I had 7 people living in my house last winter.

It is a quiet war on irrigation and use of sprinklers particularly.  Their battle cry is “Evaporation is waste!”  My landscape management teacher, in 2000, told us that half of sprinkler water evaporates; evaporation is waste; we were due for a drought; and to sell customers on drip systems.  In my 18 years of gardening professionally, I did so for the first 10 and sooner and later lived to regret it.  Drip and all other water-saving irrigation devices are delicate and don’t water completely or well, which is their point.

The war on irrigation is a direct attack on gardening, and landscape maintenance codes have not been enforced well for 20 years, mainly due to the property bubble, filling city councils with bankers, speculators and developers, none of whom want to maintain properties at all, much less to code. Weeds grow, bloom and seed unchecked on many properties, making it harder for gardeners to maintain their own places.

The ignored collateral damage of all this water saving is the budgets and lives of the poor and middle class, who are provided cheap access to water with a low base rate but must pay through the nose to use it.  They can’t afford to water lawns, trees and shrubs, or grow food.  What good does it do to let us buy vegetable seeds with food stamps, if we can’t afford to grow them?  In the ‘80s, we paid only a base rate for water, and could use all we needed or wanted.

But if the poor can’t garden, then they won’t garden for you.  They’ll work fast food.  Those who would hire gardening help are finding that weeders are hard to find.  Grants Pass is dry, dusty, and prone to weed fires, where it used to be clean, green and well kept.  Even though poverty was high and wages were low in the ‘80s, we all lived more beautifully.

Evaporation is not waste; it is part of the water cycle.  It cools, humidifies and makes rain.  It is the easiest way to share water with neighbors and other localities downwind, and to make rain in and around the place it from which it evaporates.

https://www.sciencenews.org/article/crop-irrigation-could-be-cooling-midwest 

https://www.sciencenews.org/article/watering-fields-california-boosts-rainfall-southwest

Indeed, it is hard to waste water in a city with a good sewage system and a good river with a storage dam.  Water that goes down sewage pipes is cleaned to drinking water standards and returned to the river.  Irrigation water either goes into the ground, recharging the water table; into the air to make rain, or into and through the plants, and transpired to make rain.  Even the plants we grow eventually give up their water to the cycle.

We on West Coast who live near rivers are blessed with clean rivers running west, into the prevailing wind, which blows our water vapor uphill, where it condenses and rains, filling our creeks and rivers.  The more we use sprinklers, the more rain we make. 

When I read the above article about California water boosting rainfall in the Colorado River drainage, I did a study of rainfall and temperature in Grants Pass zip code, June-September, 1983-2012.

I lived here from late ’84 to ‘86, which, thanks to this fad, was probably the height of sprinkler irrigation in California and Oregon.  We had wet thunderstorms every weekend in midsummer, though not usually wet enough to skip watering.  We didn’t have many dry lightning storms that started fires and had no fires or smoke near Grants Pass.  Watching the local news, I saw that Medford had more and larger midsummer storms than Grants Pass, and Klamath Falls had more than Medford, which fits with each city in turn adding to the water in the air with sprinklers as it condenses and falls from blowing uphill from the west.

We had a drought in ‘86 and were told not to water lawns or wash cars.  Everyone suffered equally, and paid equally for water, and our slight suffering ended with the fall rains.  That year, we had 103 days without rain, because we weren't watering lawns.

My study showed that the first decade, 1983-1992, had larger top rain events in July and August than in June and September; 1993-2003 reversed that; and 2003-2013 reversed it further.  Highest monthly temperatures also tended to increase, but lowest lows also decreased.  The amount of midsummer rain dropped nearly an inch per month per decade.

Between 1987 and 2000, I lived in Arizona.  I saw the cooling effects of irrigation in their cotton and corn fields, 10 degrees cooler in the fields than up the road in Bullhead City.  I saw the thunderstorms, torrential rains and flash floods; cold nights and hot days; the tempering effect of humidity and rain during their monsoons; and even brush fires.  Fires, floods and weather and temperature extremes are common to deserts and droughts, not a consequence of a slowly warming climate.

We have changed the climate.  First we made it wetter and cooler between the 1960s and 1980s by widespread sprinkler irrigation, and then made it drier and hotter since the ‘80s by making water use too expensive, mainly in the cities.  The resulting drying and warming has been blamed on trace gases like CO2 and methane, measured in parts per million and billion, respectively.  The former has been ignored as natural variation, rather than looking at the role of water vapor, 1%-4% of the atmosphere, and the way we keep it wetter and cooler when we use sprinklers and work the water cycle.

Why would the enviro powers-that-be push this deceptive and absurd water-saving agenda?  To gain their goal of carbon taxes, their holy grail.  But the semi-desert cities in California, Oregon, Greece, Spain, Italy and Australia that were turned into gardens and then let dry out every summer are starting to burn up (even in winter in California and the Great Plains) from all the dry weeds that these water-saving policies have grown, along with the dry forests and grasslands around them.

Water tames climate and fires

          

         It is August, and parts of California and Oregon are burning as has happened nearly every summer for the last 10 years, and in many parts of California last winter.  We are being told this is the new normal.  It was also the old normal, before we started watering with sprinklers, making it cooler, wetter and saving our cities from wildfire.

Water moderates climate and tames fire.  At 1%-4% of the atmosphere, water vapor is the most abundant greenhouse gas, holding heat by its sheer thermal mass and the blanketing effect of clouds. Yet it also cools the air during the day, by cloud shading; rain; evaporation; and transpiration through plants, which can bring the air down to 40 degrees F, the temperature at which it starts evaporating.

Evaporation is the first step in the water cycle.  That evaporation doesn’t just come from large bodies of water.  In fact, water in a body doesn’t evaporate well, because of surface tension, unless it is warm or whipped into spray by the wind.  Being near a seashore with a prevailing breeze blowing off the ocean doesn’t guarantee any rain will come of it, if the air pressure is high and the ocean is cold.  It makes fog on the west side of the coast range. It takes either a lot of heat rising from the land to pull it in from a warm sea, monsoon style, making wet thunderstorms, or a low-pressure system with wind-whipped waves to bring cooler ocean moisture onto land and make rain.

Inland, on the east side of the coast range, ocean moisture doesn’t make it to Josephine county unless a strong low-pressure system brings it in.  It was known as the Agate Desert before we started watering with sprinklers.  Extreme heat, cold, fire and floods are characteristic of deserts and drought.

When absolute humidity is closer to 4% than 1%, it is harder for fires to start and burn.  When summer thunderstorms are given moisture from sprinklers on almost all the properties in cities and the surrounding country, they make rain, not dry lightning.  This is what happened in the ‘80s, a wet decade we are told, when practically everybody in cities and country watered because water was cheap, and they wanted their yards to be clean, green and safe.

That was also the decade when water alarmists started telling us that we have to save fresh water, no matter the locality or the conditions because only 2% of the water on Earth is fresh water, and telling us that evaporation is waste.  California, and later Oregon, started instituting rationing by price, oppressing the poor and middle class, many of whom stopped watering their yards.  Many other cities around the world have done the same, drying out their cities and the countryside around them, making the world as a whole drier, hotter and more dangerous, as we saw in Greece this summer.

Thousands of single family homes in a single subdivision in Santa Rosa, California burned in Santa Anna winds last winter, while thin strips of green grass and trees out front of those homes did not. Their top water rate is $6.50 per 1000 gallons.  600 homes burned in Redding this summer, while paying $1.425 for every 750 gallons.  When people can’t afford to water, many stop cutting their weeds, because no one likes to maintain ugly.   Those weeds grow, spread their seeds, dry out, and can easily burn down their homes.

          Published at GardenGrantsPass.blogspot.com.  Like Garden Grants Pass on Facebook

Gardening is easy if you do it naturally.  Litter is tagging, marking the territory of the disorderly.

Rycke Brown, Natural Gardener               541-955-9040                 rycke@gardener.com

The Natural Gardener: Watering Is Not Waste

          Oregon water law allows any use that is beneficial.  It forbids waste, which it defines as using more water than necessary for any beneficial use or use that benefits nobody.

            Watering one’s property is not waste, even outside the irrigation season, so long as there is a good reason for it, like keeping the cracks in the ground open around a well, so water continues to flow into it.

            Indeed, it is difficult to waste water by watering, except by overwatering, which makes soil so wet it is difficult for plants to grow and encourages crane flies that eat grass roots.  This harms the yard, but still contributes to humidity.  Water that sinks into the soil recharges the water table and/or eventually flows through ground to the river.  Water that is taken up by plants grows plants or is transpired into the air.  Sprinkler watering washes plants, removing dust and fungus spores.  Water that transpires or evaporates from plants, the sprinkler and the ground makes the air cooler and more humid and makes clouds and rain.  Using cleaned city water prevents contamination from E. coli and other nasty germs.

            The water cycle works better if we work it.  In the ‘80s, at the height of sprinkler irrigation, nearly every city property and county farm was irrigated; Grants Pass was clean and green.  We had wet thunderstorms nearly every week in Grants Pass, though usually not enough to stop watering.  There were bigger rain events in July andAugust than in June and September.  There was more rain in Medford than here, and more rain in Klamath Falls than Medford, in midsummer, because everyone was watering, and water was building up and falling as it traveled uphill and downwind, filling creeks along the way.

But in the ‘80s, we started hearing that fresh water is in short supply and we should save it, regardless of local supplies and conditions.  After 30 years of “saving” water in Grants Pass and Medford by price rationing, the situation has reversed, with smaller, fewer rain events in midsummer and dry lightning being more common than thunderstorms, making bigger, more frequent forest fires.  Half of Grants Pass has gone dry, weedy, seedy, and littered in summer because so many people stopped watering, mowing and maintaining their yards.  We have had yard and forest fires in the City because of that lack of maintenance. 

I was told by a city staff member on several occasions that Oregon law requires tiered rates, or the state could take part of our water right.  I asked him to show me that law.  He could not and asked me to look for it.  I did, reading the state water manual and searching Oregon water law.  I found a law which says that the state wishes us to save water, but no mandate to do so, and nothing about unit prices or tiered rates.  I found a law which says that if a city saves enough water that it wants to do something not already in its permitted water right, it must ask the state Water Board for permission to do so. If the Board disagrees with that use, it can take that part of the city’s water right.  So, the only danger I could find to our city’s water right is if we save water, not if we use it beneficially.

          Published at GardenGrantsPass.blogspot.com.  Like Garden Grants Pass on Facebook

Gardening is easy if you do it naturally.  Litter is tagging, marking the territory of the disorderly.

Rycke Brown, Natural Gardener               541-955-9040                 rycke@gardener.com

The Natural Gardener: Price Water and Sewer Fairly

It doesn’t take a rate consultant to create fair water and sewer rate systems.  Generally accepted accounting principles would take all the fixed “overhead” costs and pay for them through the base rate, and pay for the unit costs, which vary with the amount of clean water produced and delivered, in the unit price.  This pays for the cost of providing clean water in the base rate, pays for unit costs in the unit price, and keeps the finances of the plant stable.

It takes a rate consultant, using arcane formulas, to assign overhead costs to particular customer classes’ unit rates and thus give governments, businesses, apartment dwellers and smaller households lower rates than larger families in single family homes, who are often poorer people sharing increasingly high housing costs.

When I lived here in the ‘80s, we paid $25 per month for water and sewer. The city was clean, green, and beautiful. When I moved back here in 1999 and bought a house for me and my two children, I paid between about $50 in the winter and $75 in the summer.  The difference was that the water base rate was $13 lower and unit costs were charged.  This city was drier and dustier than before.

In 2005-2006, the City hired a rate consultant to devise a water rate system that saved water, though the city had no need to do so, with large water right and a dam to keep our river running.  They lowered the base by $4 and started a three-tiered unit rate system, with higher marginal unit prices only on single family homes: not on governments; businesses; apartments; or PUDs.  My water bill more than doubled, bringing the combined bill to $140 in midsummer. 

A lot of people quit watering.  Within two years, the City had to raise the base rate $3 to pay the overhead.  It has continued to increase it since; it is now at $17.70, more than double the 2006 base rate, as more people stopped watering due to high unit prices.  My combined bill has risen to $183.

A few years ago, the City decided that people should pay for their sewer use based on winter water use, so that they would pay for every unit of wastewater cleaned.  My sewer bill doubled, from $20 to $40, as the base rate was cut and unit costs were charged.  They are now rebuilding parts of the wastewater treatment plant and raised wastewater rates 7% on both the base and the unit price per year for four years starting last February and 7% more each year for the next three.  My sewer bill is now over $70, as we had 7 people in our house last winter, up from 3.

Now the City plans a new water treatment plant.  Their rate consultant literally doubled down on tiered rates and high unit prices.  They will be voting to raise water rates soon.

State law requires that fees for government services be no higher than the cost of providing that service to each customer separately, not collectively.  Base rates for water and sewer that don’t cover the cost of overhead and corresponding high unit rates make larger households pay more per unit for water and sewer than smaller households and destabilize the finances of our water and sewer plants.  Ask the City Council to put all of our overhead in the bases, and only unit costs in the unit prices, to keep the utilities’ bills paid and the residents able to afford to use all the water we need.

Email the Grants Pass City Council and Mayor: mayorcouncil@grantspassoregon.gov

Rycke Brown, Natural Gardener               541-955-9040                 rycke@gardener.com

The Weekly Weeder: Natural Weed Control

Notice the old leaves under the rose, and the 4 x 8 sand paths.

            Weeds are taking over neglected portions of our cities and countryside, making them ugly, disorderly and unsafe.  Flowering weeds are often ugly, always disorderly, and once they dry out, they are a fire hazard.  If not killed before going to seed, they spread themselves around; they are a nuisance that multiplies.  Whole city subdivisions have burned in recent decades, and some small towns as well. When weed codes are well enforced and properties are watered, cities don’t burn. 

          The most dangerous weeds are annuals and biennials that seed and dry out in a season.  They make many seeds, some of which can last for years in soil before they sprout or rot.  But their roots don’t need to be pulled to kill them.  All their top growth comes from their crowns, the part of the plant between the roots and the stems.  Cut them under their crowns or pull them when they are flowering before they go to seed and they are gone, but it can take years to control the seeds already in the ground

          You can cut them under their crowns with scissors or a knife, which is great for going after individual weeds, but is relatively slow.  Still, this is the best way to handle seeded puncture vine, a noxious weed that pops bike tires as well as sticking shoes and bare feet.  Cutting under crowns or pulling are the only ways to take weeds out selectively in lawns, beds and borders.

          You can also beat the crowns out of the soil wholesale with a string trimmer.  This works best when the plants are young and not yet seeded, and the soil is relatively soft.  It has to be repeated to catch newly sprouted annuals and re-growing perennials.  Done often and long enough, it can kill out perennials as well.  It is rather messy.  A hula hoe (AKA scuffle hoe and stirrup hoe) doesn’t throw stuff around.

          You can mulch with leaves, compost, wood chips or bark to smother small plants and stop seeds from sprouting.  Most very small seeds need a touch of sunlight to sprout, and nearly every newly sprouted plant can be easily smothered with 2 inches or more of dense mulch.  Avoid fine bark and bagged bark with fines; bark’s natural preservatives leach downward and kill soil life, but not plants. Larger barks do not kill soil, but ¾” bark and walk-on fir are dense enough at 2” deep.  Walk-on fir bark is most effective at staying put; ¾” floats away on slopes.

          Leaves are the most effective mulch, though some tend to blow around.  Leaves that last for a year, like oak and red maple, are most effective.  They dry quickly on the surface and make a lousy seed bed for whatever falls on them.  Leaves and compost also feed soil life, which makes the soil soft for pulling weeds and provides habitat for good (predator) bugs.

          Perennial weeds like blackberries can also be fire hazards and nuisances.  Cutting under or pulling their crowns is effective, but birds drop seeds in their droppings.  When it comes to weeding, constant vigilance and watering is the key.

 

Revised 12/10/2024.  Published at GardenGrantsPass.blogspot.com

           

          Rycke Brown, Natural Gardener          541-955-9040        rycke@gardener.com