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How to Sheet Mulch or Lawn Lasagna??

Written by Ryan Nassau, Water Conservation Representative, City of Sacramento

 

Have you been thinking of removing your turf grass? This winter is a great time of year to work on landscape conversion projects. Not only is the cooler weather conducive to physical outdoor activities, but it is also a great time to prepare your soil for a productive spring planting season.

If you plan on converting your turf grass during this season into a Water Wise or River Friendly Landscape, an environmentally friendly alternative to removing turf is sheet mulching, commonly referred to as the “lawn lasagna method”. Though this method may require patience, it will provide the right environment to build up soils needed to support a beautiful drought resilient garden.

Sheet Mulching                                    

Sheet mulching is an environmentally friendly alternative to removing lawns. This method avoids the use of herbicides that leave harmful residuals in the soil which may eventually seep into the ground water. Simply put, sheet mulching is a process where a compostable barrier like newspaper or cardboard is placed over the existing grass, eventually killing the lawn. This barrier is then covered with an 8-to-12-inch layer of organic material which can include soil and then topped with 2 inches of mulch. This layering process is why this method is often referred to as the lawn lasagna or the lasagna gardening method. The compostable barrier may take 6 months or more to completely decompose (depending on the material). As the underlaying grass, barrier and compost decompose what remains is a perfect template for a new River Friendly garden, complete with soil that is rich in organic matter.

 

Materials needed for Sheet Mulching:

  • Compostable weed barrier (newspaper or cardboard)
  • Compost material
  • Mulch (organic, not rocks)
  • Hose with nozzle
  • Spade shovel
  • Tape measure
  • Gardening gloves
  • 2 to 3 additional set of hands
 

 

Steps to Sheet Mulching:

1. Prepare the Site

  • Determine which material will be needed for the job.
    • How much compositable barrier (i.e. newspaper or carboard) will be needed to cover the lawn that is being converted. This is where the tape measure will come in handy.
    • How many yards of compost and mulch will be needed? Learn how to calculate the needed amount for the project area or use the materials calculator.
  • Knock down woody plants. Completely remove invasive plants such as blackberries.
  • Mow turf grass or other low-lying ground cover so that it lies flat.
  • Some invasive weeds are difficult to sheet mulch over and should be removed by hand if possible.
    • If Bermuda grass is present, be aware that their roots are much deeper than other types of grass and may require a different removal method. Warm season turf, including Bermuda may take longer to kill.
  • Flag existing sprinkler heads if retrofitting to drip irrigation.

 

  • Edging: Dig a 4-6-inch-deep, 1 foot wide trench around the edge of your lawn to avoid runoff and to prevent mulch from spilling onto the sidewalk.

 

  • Create mounds using the leftover soil and sod from edging. Just flip the edges over so the roots and soil face up. Mounds can add natural appeal to the garden by adding height and depth. Many native plants like well-drained soil and will thrive on the mounds. 

Plant the Larger Plants:

  • Before installing the weed barrier and mulch, plant any 5 gallon or larger plants. Smaller plants can be added later. 
  • Using the spade shovel, dig a hole that is as deep, and 3 times wider than the root-ball.
  • Rough up the root ball and cut away any large roots that have circled at the bottom of the container.
  • Partially backfill the hole with soil mixed with compost, place the plant in it, backfill the hole completely and then gently press the plant in.

 

3. Add a Weed Barrier

  • Add a weed barrier that is permeable to water and air, cardboard boxes are ideal. Cardboard boxes can be found behind a variety retail stores for free. Bike shops are an especially good location due the large boxes used for shipping bikes. Be sure to check with the store management prior to scavenging through their recycling or trash. You can also buy corrugated cardboard rolls commonly used for moving purposes. Do not use plastic or weed cloth which will not degrade.
  • Overlap the pieces by 6-8 inches so the sun will not penetrate through. Any lawn showing at the end of the project will come right back. Two layers of cardboard works well.
  • Wet down the cardboard as you go to keep it in place and to allow the barrier to form to the topography of the landscape.
  • Work around existing plants by tearing and folding the cardboard. Wet cardboard is easier to tear and fold.
  • Completely cover the ground with the cardboard except where there are plants that you plan on keeping.

 

4. Layer Compost & Mulch

  • Add compost and organic mulch on top of the cardboard. Spread compost directly over the cardboard and then cover it with like mulch to optimize water conservation and weed control. This layer should include about 1.5 inches of compost covered by 3 to 4 inches of mulch.
    • Consult a local arborist or tree care company regarding mulch delivery to your home or ask us about our next free mulch distribution event.
  • The top layer of mulch mimics the newly fallen organic matter of a forest. Materials for the top layer can include chipped plant debris, tree prunings, leaves or even straw. Do not be afraid of using too much. It is better to use too much mulch than too little. Use the materials calculator to determine how much mulch and/or compost is needed

 

5. Plant the Smaller Plants

  • Punch or cut holes in the cardboard and place smaller plants in the soil under the mulch and compost. Add compost around the root ball if compost was not included in the previous layer. 


6.  Maintain your lawn lasagna

  • Check your mulch and cardboard. Some of your mulch may be displaced due to pets or other garden visitors. Be sure to keep the cardboard covered with a layer of mulch to maintain an orderly appearance and prevent it from blowing away.
  • Weeds: Pull any you see. If there is a large area of weeds, it could be where cardboard coverage is not complete or a sign that the cardboard was ripped.