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Journey to a Low Water Use Garden, Step 2: Sheet Mulch

Sheet Mulching. Having Grossly Underestimated the Quantity of Wood Chips Required, We Order More.
Lawn, You Have to Go
Lawn, You Have to Go

How to get rid of the prettiest, lushest lawn in the neighborhood AND end up with a good base for my new drought-tolerant plants? Thanks to YouTube, I quickly had the answer: sheet mulch. The basic idea is that you  leave your lawn in place, cover it with cardboard and wood chips (the sheet) and then wait for nature (and microorganisms) to turn your lawn into compost right where it is (aka mulch). Very little effort, very little expense. Sounded good to me. However, watch 10 YouTube videos and get ten variations on the theme. Here’s what I did and what I would not do again:

1. Stop Mowing. All that green grass will compost down and create the basis of your new soil. I was lucky here, my lawn had few weeds and no Oxalis. I did have a substantial bit of crabgrass in one corner–an area about 4 x 4′. The sheet mulch technique will kill most grasses and weeds, but not crabgrass, and not anything that grows from a bulb, such as Oxalis and Calla Lilly-type garden invaders. Dig bulbs and corms up. Do not attempt to separate the little bulblets from the soil–I did and it never works. Just chuck the entire shovel full of bulblets with soil into the yard waste. If you have extra soil in an area known to have had Oxalis or other bulb/corm invaders, leave the soil in place. DO NOT move it around, you’ll just spread the bad news. (Been there, regretted that.) There is a technique for killing crabgrass called “solarization” that I used successfully. More about that later.

2. Find Sprinkler Heads. My lawn had two sprinkler zones and my shrub areas also had two zones. Dig up and cap off all but one sprinker head in each zone. This sprinkler head will later be converted to the nexus of the drip system in that zone, so make sure it is centrally located. After digging up and capping off all the sprinkler heads, run water to the zone to find the ones you missed! I decided to temporarily cap off the keeper sprinkler in each zone. To make conversion easier later, I dug nice pits around them and filled them with sand, then plopped an upturned garden pot over the riser so I could find it later. This technique worked out well. Back filling with sand was Amazing Husband’s idea. It made digging up the risers much easier.

Sheet Mulching. Sprinklers Marked with Pin Flags.
Sheet Mulching. Sprinklers Marked with Pin Flags.

3. Edging. Have you ever noticed that weeds make happy between the sidewalk and the planted bed? Once you get rid of your lawn, you will have an abundance of hardscape edges abuting planted beds. Only one YouTube video mentioned edging, and I’m really happy I followed that advice. The idea is to make the edges of your planting beds inhospitable to weeds (it will also make them inhospitable to the plants that you do want, but there are ways around this. I share that trick in a later post.) Dig a trough around your lawn about six inches deep and six inches wide. Scrape any mud or dirt off the cement side of the trough. The lawn side can slope  down. When you begin sheet mulching, you’ll line the trough with a very thick layer of newspaper (10 to 20 sheet thick) and fill with wood chips. MEANWHILE, you will have a pile of dirt and grass that you have just extracted from the edging process. Many people recommend using extra dirt to create berms. I followed that advice to my great regret. Learn from my mistake and let’s discuss sculpting.

Sheet Mulching. How to Deal with Edges
Sheet Mulching. How to Deal with Edges

4. Sculpting. Sculpting the landscape before sheet mulching is one of the most important steps in your overall success. I didn’t know this at the time and made many mistakes that l paid for later in extra work and unhappy plants. Once you’ve edged, look at your yard. Is is flat? Are there high spots, or low spots? Compare your terrain with your garden design. Some plants need to be high and dry, others like it a little more wet. I’ve hiked a lot and never seen a natural feature that resembles a man-made berm. To me a berm is rather narrow and has a steep pitch. Yes, there are plants that thrive on slopes, but it is almost impossible to mimic a natural slope  in a garden setting. So people put in berms or mounds with disappoining results. When you sculpt your garden terrain, think of VERY gentle inclines.

Where did I go wrong? I took all that edging material and decided to make a couple of berms with it. Months later after I realized they were impractical and looked silly, I dug them up and redistributed the soil to flatten them out. Now they provide a gentle rise, not a mini-mountain. I also neglected to address the fairly severe slope from the lawn to the drive way. Had I paid attention, I could have used the extra material from the edging and from the patio to level off this area. You know that old adage “Measure twice, cut once?” I’ve now partnered it with , “Think twice, dig once.”

One of the great thing about sheet mulching is that you don’t have to dig up your lawn. Well, that great feature disappears when you make rash decisions about where to put extra material.

Before you start on the next step, take the time to sculpt your garden terrain. After you start laying down cardboard is too late. Dig the edging, dig garden paths and patios to the level you will need to lay your base material. You can go ahead and finish your patio and paths now, or wait. (I finished the patio, but waited on the path. The order of these things doesn’t really matter as long as you have a plan to deal with the excess material that digging a patio or path generates.)

Sheet Mulching. Prep Work on the Pebble Patio
Sheet Mulching. Future Site of the Pebble Patio. See how I piled dirt on the lawn instead of spreading it evenly? Don’t do that!

5. Place the Cardboard. Collect as many pieces of large cardboard as you can find, then get more. You’ll be surprised how much you really need. Remember, the cardboard will need to overlap by 1/3. I had great success at an appliance store by calling ahead. Amazing Husband took me dumpster diving behing an ice cream plant on a date night. We scored a massive amount of cardboard. I found it handy to have bricks, heavy stones, and stakes ready to keep the cardboard in place.
Prep the unmowed lawn and sculpted area by giving it a good watering. I know, not very drought wise, so don’t shower for a week and water your lawn instead. It’s important that everything under the cardboard is damp in order for decomposition to get a good start. Next (and this is optional) layer brown composty stuff on top of the lawn. We spread a bunch of dry leaves and the contents of our compost bin on top of the lawn. Additionally, since we removed our existing flower/shrub beds at the same, we broke up that material and spread it around as well.

On to the cardboard! (Except for that one area of crabgrass). Here is an important tip: Start laying the cardboard closest to the house and move toward the sidewalk. Lay in a nice long row parallel with the sidwalk. Over lap each piece by about one third. Make sure not even a tiny bit of lawn or compost peeks through. If you encounter a piece of cardboard that has holes, or end up with a gap between cardboard flaps, lay a nice thick layer of newspaper to fill the gap.

Continue laying the next row. By the time you reach the sidewalk, the cardboard pattern will resemble shingles on a roof. Place bricks or heavy stones on the cardboard to keep it from blowing away. You can also use stakes. Once the wood chips are in place, the cardboard will stay put.

Sheet Mulching. Cardboard in Place on a Rainy Day.
Sheet Mulching. Cardboard in Place on a Rainy Day.

6. Add Wood Chips. Ah, the final step: cover the cardboard with three to five inches of wood chips. I’m on the side of using a thick layer of chips to start with and then removing a few inches of chips when I’m ready to plant. Free wood chips are readily available from tree trimmers. We’ve been using the same tree service for over 20 years to take care our 100 year old Magnolia. When I needed wood chips, I called Bartlett’s Tree Service, explained I was using the wood chips for sheet mulch and then said I’d wait for a “good load.” “Good load” is an important phrase. Expert arborists such as Bartlett’s know what this means. It means no eucalyptus, no diseased trees, and mostly uniform wood chips with a few leaves. I had to wait a week for my free chips. My neighbor had to wait two weeks. In each case, the chips were worth the wait.

Immediately before spreading the wood chips, wet down the cardboard. (Yes, another week of no showers to make up for the water waste.)

Remember the very specific instructions above for laying the cardboard starting at the house and moving toward the sidewalk? Now, you’ll see the wisdom of this. When your wood chips arrive they will be dumped into a pile on or near the sidwalk that you will then have to spread. Because the “open” flaps of the cardboard face away from the street, it’s fairly easy to push, shove, and shovel the chips into place without them getting tucked under the cardboard flaps.

Sheet Mulching. Wood Chips have Arrived
Sheet Mulching. Wood Chips have Arrived.
Sheet Mulching. Having Grossly Underestimated the Quantity of Wood Chips Required, We Order More.
Sheet Mulching. Having Grossly Underestimated the Quantity of Wood Chips Required, We Order More.

Once your yard is covered evenly with wood chips, you have successfully sheeted. The mulching will begin soon as microorganisms, fungi, sowbugs, worms, beetles, and other decomposers breakdown the grass, leaves, and cardboard. It is surprising how quickly this can happen. I placed the last set of wood chips in my yard in March 2014 and by August 2014 there was very little cardboard left. By January 2015, all the cardboad was gone, and that three inches of wood chips had grown thin.

How to Kill Crabgrass

About that crabgrass. I read that crabgrass thrives with the sheet mulch method and that the best way to get rid of it was to solarize the soil. I did, and it worked. The idea behind solarization is to use the sun’s rays to cook the soil, killing the crabgrass and everything else. First, I pulled out as much crabgrass as possible and took a layer of soil with it. Next I watered the area really well, then covered it with black plastic. The edges of the plastic were secured with rows of bricks to keep any heat or moisture from excaping. Next I paid attention to the weather. After the area had experienced three consecutive 80 degree days, I pulled off the plastic and sheet mulched the area. I’m still kicking myself that I didn’t check the soil temperature with Amazing Husband’s meat thermometer. The goal was a soil temp of 200 degrees at 4 inches. Even without sicentific confirmation, the solorization appears to have done the job. A year later, still no crabgrass.

Such are the adventures in sheet mulching. In my mind, it is the ONLY way to get rid of a lawn. It’s cheep, requires very little labor, nothing goes to the landfill, and you end up with amazing soil without adding amendments, plus no weeds!

Sheet Mulching. One Half of Yard is Complete.
Sheet Mulching. One Half of Yard is Complete.
Sheet Mulching. This Path went in After the Sheet Mulch.
Sheet Mulching. This Path went in After the Sheet Mulch.

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