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| How To Sheet Mulch A Garden |
For years I have been promising to explain how simple sheet mulching is. Finally I prepped my own garden, and took photos of every step. I did all of the work myself and used my own camera to take all photos. Sheet mulching works better than home-improvement-store variety weed fabric, costs next to nothing or nothing at all, and is the best solution to keeping a garden during a drought. Many of my clients swear by this method to keep weeds away all year, and keep their water bill next to nothing. One client even skipped installing drip irrigation and didn't need to water even though it hardly rained! Now that's very inspiring!
A garden may be sheet mulched to establish a weed-free low-water low-maintenance garden just about anywhere. Sheet mulching is the scientifically proven++ way to grow weed-free, use the least water and grow the best plants, with almost no effort, chemicals and least expense. The best time to sheet mulch the garden is when the garden is being prepped for planting. You can sheet mulch and plant the very same day! Consider it an instant garden.
Benefits include:
- Same-day prep and planting
- Weed-free for at least one year
- Lower water usage
- Scientifically developed and proven to work chemical-free
- Immediate and chemical-free destruction of all weeds, weed seeds and weed roots
- Higher and more stable soil moisture
- Steady nitrogen food source for plants all year round
- Disease reduction (less water mean less disease)
- Vigorous plant growth
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| BEFORE - Ready to Start As-Is |
Sheet Mulch Recipe
Garden bed - planting area with soil as-is, with weeds included is fine*
Double-Thick Cardboard - enough to cover square footage of entire garden**
Cold-finished pure compost - enough to cover entire garden 1/4" thick***
Wood or Bark Mulch - enough to cover entire garden 3" to 4" thick****
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| "Stomp The Yard" |
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| Crush Weeds Underfoot |
Thoroughly wet garden bed by spraying down with hose or overhead spray irrigation system and allow the water to soak into and dampen the soil.
(*Note: if your garden soil is compacted so much, or is so clayey that the water you spray down on it does not soak in but mostly runs off, this means that neither water nor air will get to your plants' roots. This can happen if the soil was driven over or walked or run upon, such as a sports field or driveway or place where vehicles or heavy machinery were stored. You will notice that weeds not present or not as tall and thick in these areas as it is not even good enough for them to thrive. Additionally, if there is a layer of thick soil such as hard pan or a clay lens beneath, it is best to punch 6" or so holes in it every few square yards to allow water to drain, rather than pool in your garden bed. For the sake of adequate gas, vapor and moisture exchange in a healthy, friable garden soil, you must create a more aerated soil before proceeding. Shovel-turn, rototill or tractor till the soil to aerate it. Somehow the soil must be physically aerated first, if it is compacted heavily, to allow for adequate air circulation. If the soil structure itself is clayey, meaning it is mostly very fine particulates, it must have additional sized particles such as sand incorporated.)
(*Note: If you are going to the trouble of aeration, due to compaction or clay, you might as well incorporate some nitrogen material as well, for food. It is not required but may help speed up the regeneration of your garden area. Simply incorporating compost will do the trick. Make sure to use cold-finished compost. If the compost is still warm, it is still 'cooking' and may cook the roots of your plants. OMRI certified compost suppliers are supposed to be a good source, but if the soil is still warm, ask for the finished soil. If it hasn't finished, you could buy it anyway - just let it sit for about a month and it should cool down when finished.
*Most folks will not need to do any soil aeration. Chances are, if the soil is full of weeds, the weeds have already done a lovely job of aeration already, and your soil is dutifully aerated by the weeds roots. Consider yourself lucky to have had weeds pioneer your soil for you. You are now ready for the next step.
Flag anything that you need to have remain above the surface, such as pop-up irrigation heads, hose bibbs, faucets, valves, or any other such items, so that they can be kept exposed.
** CARDBOARD
Place cardboard directly on the wetted soil, right on top of the weeds, lawn, stems, leaves and all. To create double thick cardboard, you can simply open both ends of cardboard boxes and flatten the boxes so that they are of double thickness, and lay the flat boxes on the ground. If you wish to purchase large quantities of cardboard, you may acquire single-sided cardboard packing material rolls about 4' wide or so, and roll them across the surface in 2 layers. In all cases be sure to overlap the cardboard 6" so that all sunlight is blocked completely.
Thoroughly soak cardboard with a hose or overhead irrigation system.
Rip cardboard to expose any remaining equipment that was flagged in the field, such as pop-up irrigation heads, hose bibbs, valves, etc.
Spread cold-finished compost over the surface of the soaked-through cardboard in a 1/4" layer. If you like, you may spread a thickness of up to 1".
Spread mulch over the top to finish. Mulch should be no less than 2" thick, and no more than 4" thick, with an average of 3". Less than 2" offers not enough moisture retention, and more than 4" thick could result in composting-in-place where heat could damage plant roots. Straw can be thicker than 4" thick, and can go up to 6" thick without to much issue of self-composting in place.
Note: For Mulching Beneath Trees:
Taper mulch to zero thickness around the base of all tree trunks - never put mulch around the base of any tree trunks , always leave tree trunks exposed, otherwise you may kill the tree. Mulch beneath the tree is very beneficial - simply taper the mulch so that it never touches the tree trunk.
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How much Cold-finished Compost?
For backyard and small gardens:
A 40 lb bag is about 1 cubic foot, which covers about 48 square feet at 1/4" thick.
For large gardens:
1 cubic yard covers about 1,296 square feet at 1/4" thick and weighs about 1800 lbs.
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Choosing Mulch:
You can use any mulch you like, as long as it is wood or bark mulch. These days dyes are usually naturally based such as soy, and are just fine for the garden. Straw is also a very good type of mulch to use. Hay is not, as it will likely sprout. A mix of part straw and part wood is probably a good idea as straw takes a long time to break down. It provides excellent insulation, however, so for cold or hot climates it may be helpful. You can ask a local tree trimmer to deliver tree trimmings for free to your driveway, which they are very often happy to do to avoid dump fees. However I did order it once and had to give it away to my neighbors because it was a pile the size of my SUV! This worked great, wood chips, leaves and all, as it was a nice cover for the garden and looked good too. You don't have to get a full-retail priced product from a garden center for it to work. It really is about your budget and preference. Any color, shape, size and type of wood or bark mulch works great!
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How Much Mulch?
An area 10 square feet of mulch at 3" thick would be about 1.25 bags that contain 2 cubic feet, or about 0.83 bags that contain 3 cubic feet.
For larger gardens, for every 1000 square feet of area mulched 3" thick you would need about 9.25 cubic feet of mulch, or 83.3 bags at 3 cubic feet each, or 125 bags at 2 cubic feet each.
++Developed by UC Davis, taught to cities and counties nationwide for our nation's public parks and recreation areas. Free online training at Alameda County's Bay-Friendly Landscapes Program for homeowners.
