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While compost and mulch may seem interchangeable, they have distinctly different uses in your sustainable landscaping. Photo: Water Authority Compost vs. Mulch

Using Compost and Mulch to Build Healthy Soil

When undertaking a WaterSmart landscape renovation, strive to continuously feed as much organic matter as possible to the landscape soil to keep it healthy. Start first with compost and mulch to jump-start the process. Eventually, your plants will feed themselves with their own leaf litter.

Organic matter feeds microbes living in the soil that make soil fluffy. It’s similar to bread rising because of yeast.

Learn more about healthy soil in this instructional video

Compost and mulch – what’s the difference?

Compost is a soil amendment. It looks like soil and it’s hard to tell what it once was. That is because it is food scraps, landscape debris and/or manure from livestock, or biosolids (human manure) and other organic matter that already has been partially consumed and mostly decomposed by micro-organisms. Good compost brings oxygen, water, and life in one package.

Compost can be store-bought or made at home. The compost-making process, or composting, involves creating optimal conditions for the microbes to do their transformative work. When compost looks like soil, it can be worked directly into the soil. The more coarse or visible the bits of the compost are, the more likely it is to be used as mulch on top of the soil rather than as an incorporated amendment.

Compost works in several ways. First, the compost itself contains particles improving soil structure. Next, as compost decomposes in soil it encourages the formation of soil macroaggregates. The resulting macroaggregates are composed of existing soil particles and decomposed organic matter, which combine to create a more stable and better functioning soil structure.

Mulch builds soil structure over time and holds in moisture. Photo: Monsterkoi/Pixabay compost

Mulch builds soil structure over time and holds in moisture. Photo: Monsterkoi/Pixabay

Mulch is a soil topping. Mulch may be organic or inorganic material covering soil. It’s made of larger particles and looks like recycled debris. Mulch can be made from organic matter such as grass clippings, leaf litter, and shredded wood trimmings, or inorganic materials such as gravel or decomposed granite.

The microbes in healthy, biologically diverse mulch bind the organic matter together, forming a thick blanket. This cover protects soil and plant roots from temperature change, keeps moisture in by slowing evaporation from the surface of the soil, and keeps weeds from sprouting by reducing sunlight penetration to the soil surface.

Mulch always stays on top of the soil. Unlike compost, it is never worked in. Recycled organic debris is the most effective type of mulch because it builds soil structure over time and provides a durable, protective surface barrier. The smaller the debris and the more mixed leaves with wood chips, the faster it decomposes. When building soil, small and mixed is best.

Composted material, especially coarse composts, also can be used as mulch. Artificial and inorganic mulches (decomposed granite, gravel, rubber chips, and other rubble) are primarily decorative since they do not contribute to soil life or plant health. They may be used in limited applications such as pathways.

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WaterSmart Living-Logo-San Diego County Water Authority

(Editor’s Note: The San Diego County Water Authority and its 24 member agencies offer programs, resources, and incentives to improve water-use efficiency for residential, commercial, and agricultural users. WaterSmart choices are a way of life in the region. Stay WaterSmart San Diego! For more water-use efficiency resources, go to WaterSmart.SD.org.)

In the November Garden, Carry On Cool-Weather Planting, But Cut Back on Water

While fall rains have already begun, climatologists predict a dry winter, courtesy of the long-anticipated La Niña conditions. Reservoirs are at dangerously low levels. There’s little chance of their being replenished this winter, according to predictions used by federal forestry and fire agencies.

Our governor has asked all Californians to voluntarily cut water use by 15 percent. San Diego County Water Authority asked residents to reduce water use by 10 percent. No matter where in California we garden, it’s time we look hard for ways to use less water.

Saving water-water bank-Conservation Cornerrainy day can be used later. Photo": Werner Jukel / Pixabay Bank your water savings

Bank Your Water Savings for the Future

Using landscape irrigation efficiently can significantly reduce overall household water consumption while leaving adequate water in the ground to cover your plants’ needs. One tool that can help is to build up your water savings when rainfall is available.

Approximately half of the water spent by average California homes is used outdoors, mostly for irrigation. Unfortunately, up to half of commercial and residential irrigation water is squandered by evaporation, wind, improper system design, or overwatering, according to the U.S. Environmental Protection Agency.

During the winter in metropolitan San Diego County, healthy soil can absorb water in surprisingly large quantities to be released slowly to plants as they use it during drier months – like using a savings account to pay for expenses over time.

There haven’t been many opportunities in recent years to do so. However, whenever it is possible, there is no need to use the residential water supply on your landscaping when Mother Nature can bank water savings deposits for you.

Balance your water bank account 

Maximize your landscaping soil's ability to retain and save rainfall and irrigation for drier days. Photo: D. Douk/Creative Commons

Maximize your landscaping soil’s ability to retain and save rainfall and irrigation for drier days by creating a water savings account. Photo: D. Douk/Creative Commons

Water entering the soil – whether as rain or as irrigation – is like a deposit into a soil checking account.

By keeping track of those transactions of water in and water out, it is possible to know how much water in the soil “reservoir” is available in the landscape at any given time for the plants to access.

The initial soil bank balance is determined by direct observation or is assessed after a thorough wetting of the soil by irrigation or winter rains. Every day, plants take small amounts of water from the soil. Rain and irrigation fill up the water bank again. The trick is to make sure this “account” does not get overdrawn.

How can you tell when the account is depleted? Smart irrigation controllers and landscape professionals can calculate this for you. You can also rely on a soil probe, or even testing the landscape by feeling the soil surface with your fingers.

When oxygen and water are balanced in the soil, the amount of water lost through evapotranspiration is similar to paying fees on your savings account. Shading the soil surface with plant materials and mulch protects water in the soil by slowing evapotranspiration and leaving more water in your soil’s account.

This article is part of a year-long series inspired by the 71-page Sustainable Landscapes Program guidebook. The Water Authority and its partners also offer other great resources for landscaping upgrades, including free WaterSmart classes at WaterSmartSD.org.

Develop a Mulch Master Plan

How much mulch does your landscaping plan need? To develop your mulch master plan and answer this question, you first need to understand the job it will perform in different areas of your watersmart landscaping plan.

Conservation Corner-mulch-landcape-WaterSmartill you need? It depends on how you'll be using it in your sustainable landscaping. Photo: Phil Roeder/Flickr-Creative Commons License mulch master plan

Develop a Mulch Master Plan

How much mulch does your landscaping plan need? To develop your mulch master plan and answer this question, you first need to understand the job it will perform in different areas of your watersmart landscaping plan.

  • If you want to hold in moisture and keep down weeds: Use three to six inches of mulch on top of the soil
  • If you want to maintain your planting beds: Maintain two to four inches of mulch on beds at all times

Master Tip: Keep mulch one to six inches away from plant stems. When mulch crowds them, it can cause plants to rot due to moisture.

How much mulch do you need?

How much mulch do you need? First, decide how it will be used in your sustainable landscaping. Photo: Water Authority Different types of mulch

How much mulch do you need? First, decide how it will be used in your sustainable landscaping. Photo: San Diego County Water Authority

For accurate results, check these numbers:

  • Square footage of your landscaping
  • Thickness of your mulch cover in inches

Take your square footage, multiplied by mulch thickness, and divide this number by 12. The result is the amount of mulch you need in cubic feet.

Example: 891 square feet of land, multiplied by one inch of mulch, divided by 12 = 74.25 cubic feet of mulch.

Avoid these mulch types around plants

Inorganic mulches don’t decompose to feed your soil microbes and keep your plants and garden healthy and thriving. There are also some organic mulches containing dyes or other chemicals. Others such as shredded redwood take a very long time to break down.

Master Tip – These are the types of mulches you should use only in areas without plants:

  • Shredded redwood
  • Dyed wood mulch
  • Decomposed granite
  • Gravel
  • Rubber pellets

This article is part of a year-long series inspired by the 71-page Sustainable Landscapes Program guidebook. The Water Authority and its partners also offer other great resources for landscaping upgrades, including free WaterSmart classes at WaterSmartSD.org.

Mulching for Water-Use Efficiency

Even though temperatures rarely drop below freezing in most parts of Southern California, many people overlook winter when it comes to caring for their native plants and traditional landscapes. There are many things that can help keep landscapes healthy and water-efficient, especially during the winter months when there is more natural rainfall. One of these things is to use a layer of mulch to prevent water loss and insulate landscapes during colder times.

Person holding organic mulch

Mulching for Water-Use Efficiency

Even though temperatures rarely drop below freezing in most parts of Southern California, many people overlook winter when it comes to caring for their native plants and traditional landscapes. There are many things that can help keep landscapes healthy and water-efficient, especially during the winter months when there is more natural rainfall. One of these things is to use a layer of mulch to prevent water loss and insulate landscapes during colder times.

Mulch types

For maximum sustainability and to support plant health, use a locally sourced and blended organic mulch. If the goal is to create a walking trail or other area that is not intended to grow plants, consider a longer lasting wood mulch or inorganic mulch. Organic mulch may be available at low cost from local landfill recycling centers. For optimum soil and plant health, look for a mulch that has a blend of leaves, stems and woody portions of the plants. This type of blended mulch will break down over time and add organic matter to the soil to support natural biological processes, prevent erosion, maintain soil moisture and support water infiltration into the landscape. In addition, composted blended mulch has gone through a natural maturation process that kills weed seeds and pathogens.

Mulching tips

Apply a layer of mulch three to four inches deep and remember to keep it at least four to six inches away from plant stems to avoid creating a condition that is prone to disease. In areas where the goal is to build the health of the soil, avoid using weed guard type fabrics. Pulling weeds and clearing debris also helps to increase the efficiency of mulch and removes hiding places for pests.

Reduce irrigation costs

With a layer of mulch on your landscape, you can conserve water because the layer of mulch will help keep moisture in the soil – this is especially important because most plants grow deeper roots in the fall and early winter. Be sure to also manage your irrigation by setting your irrigation schedule seasonally, controlling overspray and fixing any other problems promptly.

Winter Landscape Tip: Tell your landscaper about FREE training. Webinars in English and Spanish include sustainable landscape principles and irrigation essentials. Learn more: https://qwel.watersmartsd.org.

Qualified Water Efficient Landscaper training is made possible by the San Diego County Water Authority, its member agencies and the County of San Diego.

Want more tips for water-use efficiency and maintaining your sustainable landscapes? Check the free WaterSmart education classes and on-demand videos: WaterSmartSD.org.

How to Compost the Right Way

You can make composting on-site a goal for your sustainable landscape maintenance to reduce waste and help the soil thrive. You’ll know when the compost is ready to use when it has an earthy smell, has cooled off, and doesn’t reheat when stirred. Next, look for a uniformly dark brown or even black color. You shouldn’t be able to identify any of the original particles.

Spread compost directly on the soil surface to use it as mulch. That can prevent erosion and help plants and soil filter pollution, such as hydrocarbons and metals from road surfaces. Most greenwaste-based composts can be applied to a depth of three inches. Use up to two inches of bio-solids.

If you don’t produce your own compost on site, get it from a reputable source that guarantees high quality. Commercially produced quality can vary significantly due to the diverse nature of feedstock, processes, and maturation standards.

Use compost to make healthier soil

For native plants in your sustainable landscaping, use roughly 15 percent compost by volume to repair disturbed or damaged soils.

Clay-based soil amended with compost leads to more productive and healthy plant growth at a lower cost than amending the same soil with the necessary 45 percent sand. Therefore, you can mix poor soils that are compacted, lifeless, or subsoils with about three to six cubic yards of high quality compost per 1,000 square feet to improve the soil structure.

If your compost is based on bio-solids, it can be high in ammonium nitrogen. Use this type of compost sparingly.  When using bio-solids, be sure you know exactly where they came from.

Read more at Gardening Know How: Composting With Biosolids: What Are Biosolids And What Are They Used For https://www.gardeningknowhow.com/composting/ingredients/composting-with-biosolids.htm

This article was inspired by the 71-page Sustainable Landscapes Program guidebook available at SustainableLandscapesSD.org. The Water Authority and its partners also offer other great resources for landscaping upgrades, including free WaterSmart classes at WaterSmartSD.org.

Conservation Corner-mulch-landcape-WaterSmartill you need? It depends on how you'll be using it in your sustainable landscaping. Photo: Phil Roeder/Flickr-Creative Commons License mulch master plan

More About Mulch You Need To Know

 When using mulch in your landscaping, how much mulch do you need? It depends on what job you want it to perform. 

  • To hold in moisture and keep down weeds: Use three to six inches of mulch on top of the soil. 
  • To maintain planting beds: Maintain two to four inches of mulch on beds at all times.

Remember to keep mulch one to six inches away from plant stems. Mulch can cause plants to rot. 

How Much Mulch Do I Need? 

A few simple measurements and calculations will help you determine your mulch needs. Graphic: Water Authority How much mulch

A few simple measurements and calculations will help you determine your mulch needs. Graphic: Water Authority

You first need to know these numbers: 

  • Square footage of your landscaping  
  • Thickness of your mulch cover in inches

Then take your square footage, multiplied by mulch thickness, and divide it by 12. This will give you your amount of mulch in cubic feet. 

For instance, 891 square feet of land, multiplied by one inch of mulch, divided by 12 = 74.25 cubic feet of mulch.  

Avoid These Mulch Types Around Plants 

Inorganic mulches don’t decompose to feed soil microbes and keep your plants and garden healthy and thriving. There are also some organic mulches containing dyes or other chemicals. Other mulches, such as shredded redwood, take a very long time to break down. These are the types of mulches you should use only in areas without plants, such as in pathways or dry decorative areas: 

  • Shredded redwood 
  • Dyed wood mulch 
  • Decomposed granite 
  • Gravel 
  • Rubber pellets 

Read more about sustainble landscaping: Take The Soil Test

 This article was inspired by the 71-page Sustainable Landscapes Program guidebook available at SustainableLandscapesSD.org. Hardcopies are available free of charge at the Water Authority’s headquarters, 4677 Overland Ave., Kearny Mesa. The Water Authority and its partners also offer other great resources for landscaping upgrades, including free WaterSmart classes at WaterSmartSD.org.