What’s the Deal with Sheet Mulching? | Golden State Gardens

Sheet mulching is a low-cost, sustainable landscape design practice that kills lawn and weeds while improving soil health. Learn how you can easily implement this earth-friendly practice into your Bay Area landscape- by Golden State Gardens, San Jose

Have you heard of the term sheet mulching, but are not familiar with the practice? Sheet mulching is a sustainable landscape practice that improves the soil composition by layering compost, cardboard, and mulch in the planting space. Sheet mulching can be used over living lawn, weeds, or bare soil that needs to be amended and improved. The cardboard and mulch effectively cover and solarize the growth underneath, killing the unwanted material.

Golden State Gardens recommends sheet mulching for most of our sustainable landscape designs to suppress weed growth, suppress lawn growth, and improve soil health because a healthy soil creates vibrant, happy, and fast growing plants.

Sheet mulch was applied over lawn in September 2022.

4" plants were installed in February 2022, with healthy soil.

Seven months after planting, plants are thriving. Healthy soil helped create healthy plants.

We find sheet mulching to be a superior practice to using landscape fabric, which does not decompose, prevents vital nutrients from entering the soil, and tears apart. Too often our company enters a job site and finds old landscape fabric exposed on the surface, not blocking weeds, and creating a landscape that looks unkempt.

Landscape fabric falls apart and becomes exposed on the surface. Photo from The Garden Professors.

Before you start sheet mulching your property, there are some important questions to consider:

Are you suppressing living lawn?

Since California typically only sees rain in the winter with dry summers, sheet mulching over living lawn is best done during the summer months, when it’s hot and dry. After a couple months of the sheet mulching in the summer, you can begin planting. The cardboard is relatively soft and easy to break through with a shovel. In the ground you will find softer and richer soil that is beaming with life.

You can sheet mulch over living lawn in the winter, but know that you will need to wait several months until after the rains stop and the weather gets hot before you can begin planting. Because of these reasons, it’s best to wait until the summer, if your time permits.

Image of lawn prior to sheet mulching.

Are you sheet mulching the same time you are installing plants?

If you are sheet mulching at the same time that you are installing new plants, then we recommend first removing the lawn with a sod cutter, then sheet mulching. Otherwise you risk the lawn invading the new plant material.

Sheet mulching installed at same time as plant installation. Lawn was first removed by sod cutter, then covered with standard sheet mulching procedures.

Do you want to keep some of the existing plants?

Sheet mulching can definitely be done around existing plants. Holes can be cut out of cardboard, to allow plants to grow. Established plants love sheet mulching as much as new plants.

Do weeds still grow through sheet mulch?

While sheet mulching suppresses existing weeds, it cannot suppress weed seeds that land on top of the mulch. However, Golden State Gardens has found that by creating a soil full of healthy organic matter, weeds that grow on top of the mulch are far easier to remove than soil that is bare and compacted.

Additionally, if you are planting the same time that you are sheet mulching, know that you may experience lawn or weeds that will grow next to the new plant. This cannot be avoided, and it is best to remove the weeds as quickly as possible. However, once the plants become established and grow in size, there will be less space for the weeds to germinate and grow.

Do you have Bermudagrass?

Bermudagrass management takes additional considerations when sheet mulching.

Bermudagrass is a quick growing invasive grass, and its creeping stems will develop roots wherever they touch the soil. While Bermudagrass can be a challenge to eradicate, Golden State Gardens has been successful with its removal.

To sheet mulch over Bermudagrass, Golden State Gardens recommends the following: 

a. Bermudagrass blooms around June through September, this is the best time to remove the grass because its energy is focused on producing flowers and seeds, opposed to growing stronger roots and spreading.

b. Try removing as much of the root as possible, which typically runs about 6” deep.

c. Spray the remaining exposed root system with a vinegar spray that consists of 5% vinegar, a dash of soap detergent, and water. Spray or gently pour the solution on the desired location.

d. Sheet mulch as planned.

e. Removing Bermudagrass is a multi year task until it is completely eradicated, so it’s important to stay on top of its removal as soon as it appears on the property.

Now you are ready to sheet mulch. Below is a step-by-step guide to facilitate your success:

1. Trench:

Where the lawn meets the permitter of a walkway, trench about 6” down and 1’ across. The soil that you remove can be thrown on the center of the lawn. You will be building up the soil line, so trenching keeps the soil, mulch, and cardboard from falling out of the designated space. The is especially important around pathways.

Soil was trenched along the walking path so mulch doesn't overflow into pathway.

2. Compost:

Spread a good layer of compost between the existing soil and cardboard. The compost contains vital life that the landscape needs to thrive and breakdown the cardboard. This should be about 2”-3” thick.

3. Water:

Spray the compost with a sprinkling of water to make the soil life happy and active. This step is not always done, but is helpful.

4. Thick paper surface:

Cardboard or newspaper, both can be easily obtained and used for sheet mulching projects.

While cardboard is the most common material to sheet mulch, newspaper can also be used. A thick layer of newspaper that is 1/4” thick, without the gloss pages, also creates a good barrier. Make sure that the paper surface overlays each other by 6”, so lawn cannot grow between. From Golden State Gardens’ experience, newspaper takes longer to break down and can be harder to control when the pages start to become exposed.

If you choose to use cardboard, you have a couple different options. You can purchase cardboard rolls, which makes installation quicker. Or if you want to be more environmentally friendly, you can gather saved cardboard boxes, with the tape removed. I suggest speaking with your local businesses to see if you can grab any cardboard boxes that they would otherwise throw away.

5. Water again:

Spray the cardboard with water. Again, it encourages life to eat and breakdown the cardboard.

6. Mulch:

Apply a thick layer of mulch on top of the cardboard, about 3”-4” thick. The mulch will suppress the weeds or lawn and will cover the cardboard. Over time, the mulch will break down and create a healthy layer of soil.

While some professionals apply a second layer of compost before applying the mulch, Golden State Gardens has found success with only applying a thick layer of mulch and not an additional layer of compost. Either way, you can’t go wrong.

Cross-sectional of sheet mulch. Image created by Water Authority and Golden State Gardens.

Sheet mulching is an earth friendly landscape practice that improves soil health for new and existing plants. Sheet mulching feeds the soil, which provides plants with a stronger root system, and stronger roots means plants will grow faster with less water.

Reach out to Golden State Gardens to schedule your free 30 minute phone consultation to learn more about sheet mulching or other sustainable landscape practices.