Mulch forms a layer between the soil and the atmosphere preventing sunlight from reaching the soil surface and reducing evaporation. However one should be careful because mulch can also prevent water from reaching the soil by absorbing or blocking water from light rains.
The effect of mulch upon soil moisture and mineral content is complex.
The word “mulch” does not necessarily mean wood chips or shredded bark. “Mulch” is anything that covers the soil to retain moisture, replenish the soil, and prevent weeds.
Mulch is any material that is spread or laid over the surface of the soil as a covering. Organic mulches also help improve the soil’s fertility, as they decompose. Mulch layers are normally 2 inches (5.1 cm) or deeper when applied.
Types of Organic Mulch
- Bark, Shredded or Chipped
- Composted Manure
- Grass Clippings
- Shredded Leaves
Organic mulch decomposes and has to be replaced, but in the process, it will also improve your soil’s fertility and its organic content. The dryer and woodier the mulch, the slower it will decompose and the fewer nutrients it will give to the soil.
It pays to know the origin of manure, compost, and straw since these materials can contain viable weed seeds.
The last thing you want is to spread a mulch that is going to start sprouting and make more work for you. Each type of organic mulch has its use. We discuss these further in this article.
Bark mulches are best used around trees, shrubs, and in garden beds where you won’t be doing a lot of digging.
These woody mulches don’t mix well into the soil, and it can become a hassle to have to keep moving them aside to make way for new plants.
They will, however, last longer than finer organic mulches.
Great material as long as you moisten it and mix it in with the soil and keep an eye on soil PH. It looks great, too.
Used as a soil amendment, it can add “fluffiness” to the soil because soil that is mixed with peat is much less dense.
It doesn’t get compacted, which can suffocate new seedlings or cause root veggies to become stunted because they can’t push through dense clay soil types.
Gardeners also like that its introduction to the garden causes no disruptions. There are no pathogens, bacteria, bugs, weed seeds, or other nasties to worry about as you might find in other soil amendments.
Compost and composted manure can be used anywhere, as long as they are relatively well composted and weed-free.
You can use them as a coating of mulch or simply side dress plants with them during the growing season to insulate and give a boost of slowly released nutrients.
This is the brand name of a specific type of mulch that is a combination of mulch, agricultural manure, soil conditioner, and humus. Available at sweetpeet.com
Grass Clippings are best suited to remote areas of your garden where you want to suppress weeds. Grass clippings, like most green plant debris with high water content, decompose very rapidly, and in the process, they can get somewhat slimy, with an unpleasant odor, so use with discretion.
Grass clippings also tend to mat down and not allow water to pass through. Ideally, you should use a mulching mower and leave the clippings on the lawn to add fertility to that soil.
If you do bag your grass clippings, don’t throw them away unless you have used weed killer or some other herbicide or pesticide on your lawn. Synthetic lawn care products can be bad for some flowers, and you certainly don’t want to use them in your vegetable garden.
Untreated grass clippings can either be dumped into your compost bin or used to mulch open, unplanted areas.
Newspaper as mulch is becoming more and more popular. Most newspapers have switched over to organic dyes, especially for their black & white sections. Shredded newspaper has been used for years to keep plant roots moist while shipping.
Layered sheets of a newspaper also have great moisture retention abilities, and they act like other organic mulches as far as suppressing weeds and controlling soil temperatures. They are also great for smothering existing grass, to jump-start a new garden bed.
To use as a mulch in the garden spread a layer of four to eight sheets of newspaper around the plants. Moisten the sheets to keep them in place. On windy days it’s easier to moisten the sheets before you place them down. Cover the newspaper with a one to three-inch layer of another organic mulch and the weed protection should last throughout the growing season.
Shredded Leaves are natures favorite mulch. They can be used as mulch anywhere and have the bonus of being free.
You will also entice more earthworms to your garden soil. Some gardeners don’t like the look of leaves in their garden, and they probably aren’t appropriate for a formal setting.
If you spread a layer in the spring before plants spread out, the leaf mulch tends to blend into the view within a short time. Shredded leaves are perfect for woodland gardens, and if you spread a layer over your vegetable garden in the fall, it will begin decomposing over the winter.
Unshredded leaves can mat together and repel water in rainy areas. If that happens, you can always rake and fluff them up a bit if they appear to get matted.
Straw and Hay
Straw and salt hay are popular mulches for the vegetable garden. They keep the soil and soil-borne diseases from splashing up on lower plant leaves and make paths less muddy. Straw decomposes very slowly and will last the entire growing season.
It also makes a nice home for spiders and other beneficial insects who will move in and help keep the pest population in control.
Finally, it’s easy to either rake up or works into the soil when it’s time to plant a new crop or put the vegetable garden to bed.
Examples of Synthetic and Inorganic Mulches
- Black Plastic
- Landscape Fabric
- Gravel and Stone
Which mulch you choose depends on the function and aesthetic you are looking for. Synthetic and inorganic mulches do a good job of holding moisture and blocking weeds.
They don’t add any fertility to the soil, but they don’t decompose and require replacing as often as organic mulches. Gravel and Stonework are mulches used in areas that require good drainage or beds with plants that like a little additional heat, like Mediterranean herb gardens and rain gardens.
Stone is hard to remove, so give it a lot of thought before using stone or gravel as a mulch.
The Benefits Of Mulch:
- Stabilizes soils and prevents erosion.
- Helps soils retain moisture for plant use.
- Improves soil structure and quality over time, if properly applied.
- Looks great (sometimes).
- Improves biological activity and mixes organic materials into soils.
- Prevents weed growth. Keep in mind that the definition of a weed is “a plant out of place.” If we mulch to prevent weed growth, then what is it doing to the desirable plants?
- Can be an effective herbicide in place of chemicals, cutting, mowing, etc.
The Truth About Cedar Mulch
Everyone loves cedar mulch for its color and scent.
However, it has many of the same drawbacks as other hardwood mulches, with a tendency to bind together and mat down.
A better option is to go with cedar bark mulch, which stays loose and doesn’t bind.
Mulch Is Not Perfect
Too much mulch that is improperly applied in too thick of a layer kills plants and/or prevents proper growth. Some mulch like hardwoods and shredded bark bind together, which prevents penetration of air and water.
Bad mulch also reduces the biological activity in the soil. Where are the bugs and the worms in this mulch? If they can’t live in it, how does a plant?
A badly chosen mulch can change the chemical composition of the soil. Mulch that is not fully decomposed draws nitrogen from the soil as it breaks down. Some mulch also leach micronutrients, like magnesium, that are harmful to plants.
Productive soils have variable percentages of five equal parts, including clay, sand, silt, organic matter, and biological components. Too much organic matter is never a good thing. Besides, mulch that is not clean and that contains garbage, weed seeds, or harmful pathogens.
Consider the cost of mulch.
Not All Mulch Is Made The Same:
A by-product from arborists, this is essentially someone else’s waste. It is best used if allowed to decompose for two to three years and mixed with other garden compost and organic fertilizers to aid in decomposition.
Double-ground hardwood mulch:
These are usually wood chips that are immediately processed as the byproduct of tree removal, dyed, and made available in bulk. It’s not the worst if the goal is to prevent weed growth or to stabilize soils and prevent erosion. But do not use it within the drip line of the plants or apply it around stems and trunks.
It is sold as an environmental solution to reduce the mountains of discarded automobile tires in this country. Is it a good environmental solution to grind up tires and put that in our gardens?
Plastic sheeting and fabric weed barriers:
This should only be used on a limited basis. It is best used for commercial purposes and small scale jobs. It does prevent weed growth.
However, it is also unsightly and prevents water and air from entering the soil and therefore reduces biological activity.
Cocoa Shell Bark:
Bark or mulch made from cocoa shells contains the same substances as found in chocolate and can be highly toxic to dogs and cats.
Used as a construction site soil stabilizer, straw made from barley, oats, rice, rye, and wheat hay have to seed heads that will germinate and create a major weed problem.
When To Mulch?
To maximize the benefits of mulch, while minimizing its negative influences, it is often applied in late spring/early summer when soil temperatures have risen sufficiently.
Combined with when the soil moisture content is still relatively high.
However, permanent mulch is also widely used and valued for its simplicity, as popularized by author Ruth Stout, who said, “My way is simply to keep a thick mulch of any vegetable matter that rots on both sides of my vegetable and flower garden all year long.
As it decays and enriches the soils, I add more.”
Mulch normally smells like freshly cut wood, but sometimes develops toxicity that causes it to smell like vinegar, ammonia, sulfur or silage.
This happens when a material with ample nitrogen content is not rotated often enough and it forms pockets of increased decomposition. When this occurs, the process may become anaerobic and produce these phytotoxic materials in small quantities.
Once exposed to the air, the process quickly reverts to an aerobic process, but these toxic materials may be present for some time. If the mulch is placed around plants before the toxicity has had a chance to dissipate, then the plants could very likely be damaged or killed depending on their hardiness. Plants that are predominantly low to the ground or freshly planted are the most susceptible, and the phytotoxicity may prevent germination of some seeds.
If sour mulch is applied and there is plant kill, the best thing to do is to water the mulch heavily. Water dissipates the chemicals faster and refreshes the plants.
Removing the offending mulch may have little effect because by the time plant kill is noticed, most of the toxicity is already dissipated. While testing after plant kill will not likely turn up anything, a simple pH check may reveal high acidity, in the range of 3.8 to 5.6 instead of the normal range of 6.0 to 7.2. Finally, placing a bit of the offending mulch around another plant to check for plant kill will verify if the toxicity has departed. If the new plant is also killed, then sour mulch is probably not the problem.
Mulch Can Be Living?
Groundcovers are plants which grow close to the ground, under the main crop, to slow the development of weeds and provide other benefits of mulch.
They are usually fast-growing plants that continue growing with the main crops. By contrast, cover crops are incorporated into the soil or killed with herbicides.
However, live mulches also may need to be mechanically or chemically killed eventually to prevent competition with the main crop.
Some groundcovers can perform additional roles in the garden such as nitrogen fixation in the case of clovers, dynamic accumulation of nutrients from the subsoil in the case of creeping comfrey (Symphytum ibericum), and even food production in the case of Rubus tricolor.a
Quality biodegradable mulches are made out of plant starches and sugars or polyester fibers. These starches can come from plants such as wheat and corn. These mulch films may be a bit more permeable allowing more water into the soil. This mulch can prevent soil erosion, reduce weeding, conserve soil moisture, and increase the temperature of the soil.
Ultimately this can reduce the number of herbicides used and manual labor farmers may have to do throughout the growing season. At the end of the season, these mulches will start to break down from the heat. Microorganisms in the soil break down the mulch into two components, water, and CO2, leaving no toxic residues behind.
This source of mulch is even less manual labor since it does not need to be removed at the end of the season and can actually be tilled into the soil. With this mulch, it is important to take into consideration that it’s much more delicate than other kinds. It should be placed on a day which is not too hot and with less tension than other synthetic mulches.
These also can be placed by machine or hand but it is ideal to have a more starchy mulch that will allow it to stick to the soil better.
Not So Biodegradable Mulch…
Polypropylene mulch is made up of polypropylene polymers where polyethylene mulch is made up of polyethylene polymers.
These mulches are commonly used in many plastics. Polyethylene is used mainly for weed reduction, where polypropylene is used mainly on perennials.
This mulch is placed on top of the soil and can be done by machine or hand with pegs to keep the mulch tight against the soil. This mulch can prevent soil erosion, reduce weeding, conserve soil moisture, and increase the temperature of the soil.
Ultimately this can reduce the amount of work a farmer may have to do, and the number of herbicides applied during the growing period.
The black and clear mulches capture sunlight and warm the soil increasing the growth rate. White and other reflective colors will also warm the soil, but they do not suppress weeds as well.
This mulch may require other sources of obtaining water such as drip irrigation since it can reduce the amount of water that reaches the soil.
This mulch needs to be manually removed at the end of the season when it starts to break down it breaks down into smaller pieces.
If the mulch is not removed before it starts to break down eventually it will break down into ketones and aldehydes polluting the soil.
This mulch is technically biodegradable but does not break down into the same materials the more natural biodegradable mulch does.
Some organic mulches are colored red, brown, black, and other colors. Isopropanolamine, specifically 1-Amino-2-propanol or DOW™ monoisopropanolamine, may be used as a pigment dispersant and color fastener in these mulches.
Types of mulch which can be dyed include wood chips, bark chips (barkdust) and pine straw.
Colored mulch is made by dyeing the mulch in a water-based solution of colorant and chemical binder. When colored mulch first entered the market, most formulas were suspected to contain toxic, heavy metals and other contaminants.
Today, “current investigations indicate that mulch colorants pose no threat to people, pets or the environment. The dyes currently used by the mulch and soil industry are similar to those used in the cosmetic and other manufacturing industries (i.e., iron oxide),” as stated by the Mulch and Soil Council.
Colored mulch can be applied anywhere non-colored mulch is used (such as large bedded areas or around plants) and features many of the same gardening benefits as traditional mulch, such as improving soil productivity and retaining moisture.
As the mulch decomposes, just as with non-colored mulch, more mulch may need to be added to continue providing benefits to the soil and plants. However, if mulch is faded, spraying dye to previously spread mulch to restore color is an option.