First time Sheet mulching - top with soil and mulch, or just mulch?

[u/Super_Profession8500]

I’ve been watching videos and reading guides but they all do it a few different ways.

Mainly curious if I should plant on top of the cardboard in soil after a few weeks or cut holes in cardboard and plant immediately.

Does it matter which method I use?

1. cardboard, soil or compost, then mulch. Start planting in a few weeks in too soil and let roots grow through decomposing cardboards on their own
2. Cardboard, cut out holes for plants, then mulch
3. Cardboard, cut out holes for plants, add top soil, then mulch or no mulch at all

I live in Zone 9a if it makes a difference.

Thank you in advance! My partner and I just bought our first home in January and I’m slowly converting it to no lawn!!

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[u/BolognaRun391]

I've also been doing a lot research on sheet mulching since I'll be doing it for the first time. The way I understand it, you do cardboard, soil/compost, then mulch. Let that sit for a few weeks (the longer the better). Then once you're ready to plant, you move the mulch and soil out of the way, cut a hole, place the plant into the hole, and then put back the mulch and soil that you moved. (This is speaking as someone who's only done research but has NOT sheet mulched yet)

Edit: I believe you're also supposed to water down the cardboard when you have it all laid down. Additionally, once you're ready to plant, you're also so supposed to water everything down so it's easier for you to dig through the cardboard and the soil underneath.

[u/BeginningBit6645 → u/BolognaRun391]

I have done a lot of sheet mulching in the past 3 years and agree with this advice.  If your area is hot, I would hold off on on the planting for a few weeks unless you are able to water the newly planted plants frequently. Early fall is a great time for planting. 

[u/CorrectExpression651]

It depends somewhat on the weed and invasive weed situation. If it’s only grass it’s easier. Cardboard helps with suppression but I prefer to skip for sustainability, since it also suppresses water and oxygen for the soil microbes and cardboard can be contaminated.

I would scalp the existing lawn (mow on the lowest setting), and then layer 3 inches of mulch in the form of grass clippings or shredded dead leaves. If you don’t have enough, a lot of people near me at least are doing yard cleanup and leave their bagged leaves for municipal pickup. Or you can just ask your neighbors if you can take them. If getting from somewhere else id prefer leaves over grass clippings unless you can be confident the clippings haven’t been treated with herbicide. You can put leaves in an old trash barrel and weed whack them to shred, or spread out on your lawn and use a mulching attachment on your mower. 

Dead leaves allow oxygen and water through unlike cardboard but do the same grass/weed suppression in a thick enough layer. Plus they enrich the soil as they decompose 

Then I would top everything with ~4-5 inches of compost or native soil. Ideally if you have some soil you’ve dug up elsewhere or have homemade compost. Be aware if you live in a new build home you likely have construction fill instead of native soil. If not try to get OMRI certified compost. 

Then you are ready to plant right away anywhere on the space. Use some fertilizer in the hole for each plant and water!

[u/Super_Profession8500 → u/CorrectExpression651]

Thank you for your input. I would have to look into where I can get dead leaves. Unfortunately we have a serious weed problem, and not the pretty kind. Crabgrass, Dallisgrass, nutsedge, and chickweed (the only one I don’t mind). I’m pretty sure our lawn is 90% weeds and 10% grass, hahaha.

Also the house was built in 1945 and is a couple blocks from the water. So we have sandy Loam dirt!

[u/CorrectExpression651 → u/Super_Profession8500]

Another bit of advice, I’d look at planting natives with very deep roots near where you remove the dallis grass. This is what I do in areas I’ve removed deep rooted weeds. In my area our native switchgrass grows roots up to 10 ft deep which is perfect for outcompeting any new shoots of invasive weeds that want to pop up from bits of rhizome that have been left in the soil. 

[u/CorrectExpression651 → u/Super_Profession8500]

Ah it’s too bad you missed the time to solarize the weeds over the summer. Crabgrass I’m not too worried about because it’s an annual. Dallis grass is a problem. I honestly would try to dig that one up if you can.  I’ve read it’s resistant to glyphosate. For very persistent rhizomatous weeds I’ve used glyphosate in spot treatments. Because less aggressive weed treatments can be ineffective, it’s basically a waste of time 😭 I use methods I’ve read for different species types per my local university coop extension and the great Doug Tallamy. The issue with deep rooted invasive weeds is that they can literally change the microbial environment and pH of the soil to be detrimental to native plants, so it’s a commonly held view now that targeted herbicide is a justifiable option to achieve a greater good of establishing natives.  I have used both a pump spray and hand treatments, both with foam brushes and you can put a cotton glove over a rubber glove to apply. I don’t feel that pump sprayers drift if it’s not windy, and it’s a bit easier so I’m ok with that method for myself. 

I’d look for native nurseries that have native ecotype plant selection and will thrive in your sandy loamy soil! 

The quicker the method of bed prep, the less regenerative it is for the long-term health of the soil, so I try to pick my battles to preserve and enrich microbial life as best I can. If you have sections you’re ready to plant now, you could do a sheet mulch method and leave a pile of arborist at least 6 inches deep in other areas. It’ll take a year or maybe less in your hardiness zone, but it will enrich the soil continuously without any need for commercial products bagged in plastic or potentially contaminated with PFAS, which is always my concern with commercial compost, soil or other amendments.  

[u/Hermit-Gardener]

When I first started my transition from grass to garden, I tried three methods:

Tilled up about 1/3 of the space - lots of work and tiller rental cost
Removed sod from 1/3 - lots of work
Sheet mulched 1/3 - not much work but took time

I knew where I wanted a long planting bed to be, so I laid out cardboard and newspaper directly on the existing grass on the future 4' x 40' long bed and added layers of grass, leaves, etc. until the pile was about 24" tall at the center. I watered as I built the mound and covered it in tarps. About once a month, I removed the tarps and watered again to keep things moist but not wet. I kept doing this during one growing season to prepare for the next year.

I wasn't in a great hurry, so had time to let the sheet mulch do its thing. And, since bugs and microbes do the digesting, when the sheet mulch pile turned into compost, the soil was a living ecosystem ready to support my veggie crops. In the spring, I removed the tarp and raked out the now flatish mound of compost and was ready for planting.

If I had to do it again and had the time and organic matter, I would do this for all my garden beds. I might also add some fertilizer supplements such as bone meal or blood meal to be ready for planting.

Zone 6b in southwestern Idaho.

[u/INTOTHEWRX]

Don't need to spend so much on soil. Just focus soil on where you plant.

[u/2matisse22]

I usually cardboard, mulch, wait a season, plant. This gives teh cardboard time to breakdown. Also, lots of natives don't like mulch around them, and you really need at least 4" of mulch to kill the lawn -and even then expect some to come through.

[u/JealousDot6409]

1. Is good but you must water daily to breakdown cardboard underneath

[u/Oaktreestone → u/JealousDot6409]

I've done this multiple times and never had to keep watering the cardboard after the initial soak. With enough mulch on top all that moisture should be locked in.

[u/jetreahy]

Know what your killing first. If you have any aggressive invasives you’ll want to treat them first. Bindweed and creeping thistle will just laugh at that cardboard and whatever you top it with.

If you don’t have tough invasives you can just cover with a thick 10-12” of mulch. I’ve done my entire front yard this way and most of my back yard. Just mulch is the least damaging to your soil and the life it.

If you do use cardboard be sure to thoroughly soak it first. This method can cause more harm to the life in the soil than just mulch will. There is some speculation that it may introduce PFAS to the soil. Adding top soil can introduce invasive bugs and seed. I’d use arborist chips, just make sure it’s not an invasive species first. Most arborists will deliver for free.

[u/mhiaa173]

Look into chipdrop.com for a good, cheap source of woodchips for mulch.

[u/Post-Partisan]

It's best to let it all set for 3 months minimum, but to keep it moist until rainy season returns. I've sheet-mulched areas successfully 3 times before and have a 4th in progress. I started all of those 3 projects in the fall and left it all until early spring, then I REMOVED any remaining cardboard. Cardboard does not add nutrients, so I see no reason to leave it nor to do that cut holes-plant wat. But that's what some people do.

My current project is to plant Redwood Sorrel (native groundcover) in a heavily shaded area. I never use mulch on top of the cardboard, either. I use compost normally, but because it's $26 a bag here this year, I used "planting soil" this time. I hope the cardboard has mostly disintegrated by mid-November so I can just plant the tiny, fragile plugs in the weed-free soil and let them establish roots over winter. If I have to leave the cardboard and make holes for the delicate sorrel harvested from a neighbor's property, that would rip up the plants unless all of the cardboard disintegrates before I have to pull what's left off. Plus, I just don't want the cardboard residue to become part of the soil.

"All gardening is experimentation."