Sheet mulching is an organic method for creating a planting bed over lawn or weedy area. It generally utilizes cardboard or newspaper as the weed barrier. Since initially writing this article in mid-2014, I acquired some information about sheet mulching; specifically the use of newspaper or cardboard as weed barrier. I’d like to share what I learned.
While browsing on the Garden Professors Facebook Page, a question was asked about sheet mulching, and to my surprise the Garden Professors said to be very careful using a paper product as a weed barrier for any sort of non-crop application. I have read in numerous places over the years (it’s all over the internet!) how using paper products as weed barrier is the organic gardener and permaculture choice. Then again, those are food-growing activities, and perhaps that is the difference.
But the science about use of paper products in non-crop settings gives us something to ponder. See Linda Chalker-Scott’s article on paper-based sheet mulch. Studies suggest there can be problems with paper products including: it can attract pests like voles and termites, it can create anaerobic conditions on overly wet and poorly drained soils; it can become hydrophobic when allowed to become overly dry when used in situations such as xeriscape gardens.
This is not to say that we should not at all use paper product as weed barrier for non-crop application. Linda Chalker-Scott says, “Newspaper and cardboard sheet mulches have been effectively used in home gardens where soil is continuously worked and irrigation is applied. For less well maintained sites, they are not the best choice…”
So I’m putting on my science thinking cap. I can guess that in agriculture situations, the soil is worked enough, and the paper is kept moist enough to compost quickly because the garden is properly irrigated. And by definition, one would do agriculture on well-drained soil. So I’m guessing if you can do your paper-product sheet mulching for ornamental gardens on well-drained soil, and you can commit to keeping the paper moist (like a well-wrung-out sponge — as we do for compost piles) during the composting period (which may be extensive), then the overly wet and overly dry situations, which can cause problems, can be avoided.
Bottom line seems to be: we don’t want a ‘sheet’ covering the soil that can in any way deter water and gas exchange between air and soil. Overly wet = not good. Overly dry = not good. Well-wrung-out sponge = just right!
How I would sheet mulch to create an ornamental planting bed using paper products on well-drained soil:
- Mow turf or weed area extremely close to ground. Leave the clippings in place.
- Dig trench around outer edge of area to be sheet mulched. The soil can be tossed toward the middle of the bed and will create a nice berm to add interest to your new garden bed.
- Install whatever edging you will be using to a height that will adequately contain the depth of organic mulch you will use on top of the sheeting. You can eliminate the need for the raised edging by being sure the trench you dig is the depth of the total amount of sheeting, soil and mulch.
- Be sure the soil is quite moist before you start laying the paper sheeting. Water it well the evening before.
- A thin layer maybe 1/2″ deep of compost or other high-nitrogen material can be laid down on the moist soil if the clippings from mowing don’t product about 1″ of material. This is not necessary, but it can help jump-start the composting.
- Lay paper product, overlapping the pieces; cardboard or newspaper 6–8 sheets thick. Don’t use color-printed (unless you are sure it’s soy ink) or gloss-coated paper.
- Water the paper. If windy, you’ll need to water it as you go to keep it from blowing around. But before covering the paper with soil be sure all of the paper is saturated. This may take a few shorter repeated watering sessions.
- Cover with woody mulch like arborist chips at least 6–10″ deep if you can let the area be dormant for a year or more before planting. If you need to plant sooner, cover with 4–6″ of compost, and top with woody mulch about 3–4″. Compost is growing medium, and if left un-mulched you’ll need to weed the area often.
- Water as often as necessary to keep paper product (and soil around it) moist as a well-wrung-out sponge until the paper is well on it’s way to being consumed by worms, microbes, etc. The woody mulch layer on top can dry out, but not the paper product layer until it’s a least partially composted.
- If you need to plant sooner than later, be sure to punch a hole through the paper layer for each planting hole. And if you’ve used a very heavy layer of mulch, you may need to add a bit of compost to the planting hole for a very small plant so it’s root area is in growing medium rather than woody mulch.
What if you don’t have well-drained soil?
As Linda Chalker-Scott suggests, you should consider not using paper product sheeting if you don’t have well-drained soil. Then your choices might be:
- Chemically kill the existing vegetation, then dig the trench, add 3–4″ compost, then top with 2–3″ fresh woody mulch (like arborist chips).
- Strip off the turf, then turn it over before applying 3–4″ compost followed by a very thick layer of fresh woody mulch (like arborist chips). Perhaps 6–10″ or more; and then wait patiently. Using this second non-chemical method, I would want to wait a while, even a full year, to see if any of the vegetation I was trying to kill below had survived. It would truly suck to plant a new ornamental bed only to have turf grass or even worse some noxious weed start to spring through the mulch.
If you do not have well-drained soil, but you still want to use paper sheeting, follow the directions in the section above this one and then regularly check the moisture condition of the paper inside your new bed to be sure its composting progress is moving along nicely. But from what I have read, it seems that a very thick layer of arborist chips and a lot of time will make a bed on poorly draining soil quite nicely without paper sheeting.