Sheet mulching for drought-tolerant gardens in California...an Ultimate eco-friendly lawn replacement method
Looking for a fast easy way to replace your dead lawn without removing soil nutrients?
Sheet mulching is a quick sustainable method for adding quality to your soil and blocking weed seeds. It is the quintessential method for building topsoil on a budget. You can use all recycled and found materials to smother weeds, improve your soil quality and lock in moisture so your landscape needs less water.
image credit: Alameda County Stop Waste Program
Should you sheet mulch your dead lawn?
Things to consider for sheet mulching:
It will raise your final soil height 2-6” … If you’re worried about dirt spilling over onto a lawn or sidewalk you may need to add a border or end the sheet mulch half a foot from sensitive sides.
Are you replacing with native lawn grass or perennial plants? If you’re replacing your old grass with new sod DO NOT SHEET MULCH. The time it takes for the under layers to breakdown may prevent your sod from rooting adequately.
If you are replacing your lawn with low-water perennial plants sheet mulches are GREAT! They save the soil nutrients still in your lawn. And they allow the dead lawn grass to compost. Digging out your lawn and adding topsoil works just fine too, like most landscapers do. It just sends a bit more stuff to the dump and causes more soil degradation than is necessary.
If you are replacing your lawn with cactus or extremely low-water natives, consider mulching over cardboard with a thick layer of DG (decomposed granite) or gravel. You can seed California poppies into DG.
What's a sheet mulch?
Sheet mulching is a fast free organic way to build a new garden. It consists of:
- A biodegradable weed blocking layer: wet cardboard or 10 layers of wet newspaper
- Soil amendments and/or top soil
- Lots and lots of mulch: woodchips, bark, shredded leaves, straw, dye-free natural materials are best (mulch much? here's an article on mulch options)
Also referred to as “lasagna” gardening, sheet mulching can be tailored to any type of landscaping. Sheet mulches for veggie gardens are often 7-12 layers thick with tons of straw and manure. For low-water landscaping, a simple layer of wet cardboard and a crap ton of mulch will do. Though we’re going to go over a few ways to dress it up below.
Why Sheet Mulch?
Help aerate soil - the roots of your dead lawn act like little canals that maintain your soil structure and help feed the soil food web as the plant remains decompose. Removing dead lawn further dries out and removes your topsoil layer.
Feed the worms - worms love wet cardboard and straw, it’s like their candy. And worm poop is the world’s best fertilizer (well technically it’s more of a micronutrient - think a greens smoothie).
Sheet mulching can be done for free - by getting free mulch from a local arborist or city green waste depot. It might eat up a day or 2 of your time but it's good to have a reason to get outside right? The Permaculture execution style is to invite some friends, family or neighbors over to crank a sheet mulch out in an hour or two. This can be done easily if you have all your materials and tools ready when they arrive. And feed 'em some decent bbq after.
How-to Improve Drainage for Drought Tolerant Plants
Good Drainage is essential for drought tolerant plants. Many California natives won’t survive without good soil drainage. Unless you are 100% sure your soil has excellent drainage (if it’s very sandy, steeply sloped or rocky etc.) it is worth adding some fast-draining rock (lava or sharp gravel) to the bottom of your planting holes. This means you need to account for your hole being a bit deeper than your plant's pot.
Ruth Bancroft perfected this technique in her rare cactus garden. She grew all manner of succulents and xeric plants in a region of California where temperatures range from -20 to +115 degrees Fahrenheit. By building large mounds of rock and sand to plant her cactus into when she designed it, she created one of the world’s most successful xeric gardens. At home you could do this by mixing in substantial amounts of sharp gravel or DG into your garden beds. And adding lots of rocks. But with sheet mulching we don’t have to go quite that far. Simply by adding a drainage layer to the bottoms of your plant holes you can ensure your new drought tolerant yard can last with less water.
Add 3-6" deep of packed lava rock or sharp draining gravel to the bottom of your planting holes to ensure drought tolerant plants have enough drainage.
How to sheet Mulch over Dead Lawn
Note: California Watersmart has some differing recommendations from mine (see simple Watersmart sheet mulch: read here). They're planting smaller plants directly into the sheet mulch in this example. This method works especially well if you wait one year for the mulch to breakdown a bit and add topsoil in your mulch mix. The method I'm listing below is for planting larger plants and sheet mulching at the same time.
- Let your lawn die (congrats you already did it if you live in L.A.!!!)
- Arrange your plants and dig their holes - this can also be done after the sheet mulch is done. Doin it first keeps your sheet mulch more in tact. And it's less of a hassle than cutting through cardboard.
- Spread your amendments over the area to be sheet mulched - even just a little bit of azomite, mycorrhizal inoculant, crab meal, light compost or worm castings can go a long way - see our article on favorite soil amendments and where to buy them by clicking here
- Soak your cardboard in an empty garbage can filled with water works great!
- Layout your wet cardboard1-3 layers thick over the dead lawn and soil amendments. Ensure the edges overlap at least an inch (so the weeds can't get through)
- Add a layer of garden topsoil 2-6” thick if you’re using it. Typically this has to be purchased. It's a great thing to do if you plan to add more plants directly into this new soil layer soon.
- Mulch! Add your mulch thick enough to fully cover the lower layers. A minimum of 3". Curious about where to get free mulch or what types of mulch you can use? Check out this article on free mulch resources.
- Check your holes are the right depth* for your new plant's crowns to be 1-3” below the height of the final mulch layer. A plant crown is the sensitive base where a plant's trunk meets the soil. 1-3" deep should have your plant crowns relatively close to your cardboard layer.
- *Put 2-4” deep of lava rock* or sharp draining gravel into the bottom of your planting holes. This will ensure adequate drainage for your low-water plants, greatly extend their lifetime and your boost garden’s success rate.
- Now Plant: After you've planted your plants into their holes, water everything (including your mulch!). This soaking will compact everything. A good drenching will hit the refresh button on your yard's little ecosystem and help settle all the new materials and plants into place.
Pro Install Tip: Soak your plant for 5-10 minutes in a bucket of water to fully saturate their root balls. The long drink helps to give them a fresh start for rooting into their new homes.
BEST PLANTING PRACTICES
-Ensure the crown of your new plants is 1-3” below the final soil grade (the final height of your mulch layer). Sheet mulches typically compact 1-2” after being watered in. If the tops of the plants sit high above the sheet mulch layer the delicate surface roots will dry out quickly*. If they get planted too deeply below they are likely to get too deeply buried and suffocate or drown over time.
*some extremely drought adapted plants (like manzanita) are planted above final soil grade with their soil mounded up around them so that they have more extreme drainage.
-Try and keep the bottom of the hole as level and decently packed as possible before putting the plant in. This prevents settling or sinking of your plant.
-Add your amendments at the soil surface not in the hole (this is different from vegetables/annuals).
-Time your transplant for a cooler time of day like early evening or early morning. Or when weather is overcast. This helps to reduce transplant shock.
FYI Native Plants Can Have Low Soil Fertility Needs
While most of our soils are so beat up and degraded a light dressing of compost won't hurt, keep in mind that most California native plants, ground covers, cactus and succulents are sensitive to high doses of nitrogen or other conventional fertilizers. Mushroom, sheep, cow and horse manure are all great in light doses but chicken manure's likely a little too much if you're planting an all drought tolerant or native garden. Worm castings and thoroughly broken down garden compost are great.
*Just a note our Alt Lawn Ultra groundcover product also has low soil-fertility needs and can be killed if conventional lawn fertilizer is used
Getting into your shovel? Consider putting a swale in for a fast effective rainwater harvesting that benefits your landscape. Swales are trenches dug parallel to slope contour that act like water breaks. They catch overland flow and re-infiltrate rain water and runoff back it into the soil. Swales can also be used for dispersing laundry2landscapes grey water systems (where your laundry water is used to irrigate your landscape) which require no permit to install in the state of California. It's best to fill swales all the way to the surface with woodchip. This way it filters out impurities. And the dry surface at the top acts like a walkway.
Plant your thirstiest plants on the downhill side of the berm created from the soil dug out of the swale. In the driest climates you can even plant right into the swale (best for food production)
photo credit: the green directory