Let’s talk about mulch. If you have been following our posts or reading or website, you are probably aware that mulch plays a huge role in our organic system. Mulch fills this role because it is so important to soil health and long term management of the soil, that it almost always is a part of any solution or process that we advocate in our gardens and landscape.
Generally, we speak of mulch without reference to what type. It is a simple word, and most people think of the stuff that you buy in plastic bags at the garden center. The problem is that there is so much more to mulch than the stuff in plastic bags.
What is mulch?
Think about walking through a forest floor. Look down and see what is under your feet. Look at the material covering the floor of the forest. It ranges in size from fallen tree trunks to the tiny remains of almost microscopic insects. On top, you find leaves, branches, twigs, and bark in identifiably large pieces. Rake back a few inches and the material starts to get finer and darker. There are still identifiable chunks and bits. Move some more of this material and you eventually get to a layer where there are no identifiable materials. It is rich, dark, and smells good. That is freshly decomposed mulch. We call it soil. Everything above that layer is mulch in one of its various stages of decay.
So mulch is almost anything decomposes into organic matter.
Mulch can also be inorganic. For our purposes, inorganic mulches are those materials that do not decompose readily but we can use to gain some of the benefits of organic mulch.
Type of Mulch – Organic
You should now know from the short discussion above that organic mulch is anything made from living material which will rot or decompose over time. Wood chips, pine needles, leaves, and grass clippings can all be used as mulch in the right place and with the right preparation.
Type of Mulch – Inorganic
Inorganic mulch is made from any material that was never alive and considered inert. Crushed rock, lava rock, plastic sheeting, and glass are all considered to be inorganic mulch. The problem with inorganic mulches is that they do not allow the natural processes and cycles to work. These materials are inert and do not decompose to return nutrients to the ground as do organic materials.
Types of Organic Mulch
Organic mulches have so many benefits in the garden and landscape that they are almost too many to list. Studies have shown that a three-inch layer of organic mulch can lower the soil temperature 25 to 30 degrees F. This reduces plants stress and water requirements. High temperatures in the soil also inhibit plants ability to access nutrients from the soil. USDA studies have shown that in some plants species, mulched plants produced three times the yield of unmulched plants. Studies in Austin, Texas, show that on turf lawns that were mulched with 1/2 inch of compost each year, a savings of $50–$200 per month on water bills.
Types of Organic Mulch – Bark Mulches
You can find bags of this mulch in huge stacks and pallet loads at the home and garden center of your local big box store. This material is made from the outer bark of trees and is a by-product of the wood industry. There are some problems with wood bark as a mulch. As the outer layer of a tree, wood bark is the trees first defense against pests and diseases. Wood bark contains a substance called suberin. This naturally occurring substance waterproofs the bark and prevents the bark from decomposing. The presence of the suberin prevents the wood bark from decomposing. Also, when it does finally decompose, wood bark contains very few nutrients and almost no micro-nutrients. It does very little for the soil.
Types of Organic Mulch – Cedar Mulches
Second only to bark mulch, cedar mulch is probably the most plentiful of the bagged mulches that you find at your local garden center. These cedar mulches come in several varieties. Some are in actuality juniper mulches, made from the leftover materials when juniper trees are cleared. True cedar mulches can be fresh ground from land clearing operations or can be flake materials leftover from de-oiling operations. The cedar flakes have been cooked to temperatures up to 2250 degrees to remove the oils and so have little, or no moisture left. They are low weight and easy to handle. The problem is that they have a very high carbon to nitrogen ratio and rob nitrogen from the soil as they begin to decompose. Just the opposite of what we are trying to accomplish. De-oiled flakes have almost no nutrient value.
Cedar as a whole is a very rot-resistant wood and, when flaked, chipped or ground, retains those compounds the resist decomposition. These substances prevent cedar mulch from decomposing rapidly. Cedar is best composted until it is well into the decomposition stage before being used as mulch.
Type of Organic Mulch – Native Mulches
When we speak of native mulch, we are talking about mulch made from recycled fresh green tree and brush material that comes from the area where it is going to be used and as freshly ground as possible. You probably won’t find native mulch at your local garden center. Your best option to find a tree maintenance company who will deliver or allow you to pick up freshly ground local material.
Native mulches have a higher percentage of green material. This green material includes leaves, buds, shoots, and green twigs. These materials are rich in proteins and other nutrients and are present in much greater numbers than what in bagged mulches. This material is much better at promoting health in the soil and the growth of the soil-biome.
Types of Organic Mulch – Composted Native Mulch
Composted native mulch is the Cadillac of mulch. The is native mulch material composted in such a way the heat generated in the compost pile kills any pathogens or weed seeds that might be present. Composting also concentrates the nutrients and helps stabilize the nitrogen. The natural decomposition that occurs during composting also begins the process of breaking down the lignin and cellulose of the raw material, which makes the compost less palatable to wood-eating insects such as termites.
Types of Organic Mulch – Stray/Hay
Straw is the dried stalks of grains after the seed heads are harvested. Usually a pale gold color, it is a good mulch. It should be applied 4 to 5 inches deep in ornamental beds and 8 to 10 inches deep in vegetable beds. We often use straw on beds that we are laying fallow over the winter. We put it on extra thick and allow it to decompose naturally over the winter. We pull it aside or remove some when we get ready to plant.
Hay is a mixture of grasses that are cut, dried, and baled. This material may include seed heads, weeds, and clover. Hay can be used as a mulch but we try to avoid it. All too often the seeds and weeds will germinate and we are left with a bigger mess than when we started. The other and more important problem with hay is that most of the producers use synthetic chemicals to control broadleaf weeds and noxious plants in their fields. The residue of these chemicals in the hay may leach into your soil as the hay is rained on and decomposes.
Types of Organic Mulch – Newspapers
Newspaper, or almost any paper for that matter, make good mulch. To be effective, it should be shredded. Almost all newsprint ink is now soy-based and is non-toxic. There are some papers you should avoid. Any paper with s slick or enameled surface should not be used. Anything printed with brightly colored inks are also suspect as some colored inks still contain some questionable products. About the only time we use paper is when we do a lasagna garden startup. The paper we use is brown cardboard and it is not shredded, but laid out flat to serve as a biodegradable weed barrier.
Types of Organic Mulch – Compost
Compost is a high-quality mulch when applied 3 to 5 inches deep. It has a high nutrient content, doesn’t wash out or float away during rains and, if composted properly, does not contain viable weed seeds. To get the best results, use partially complete (green) compost for mulch. It is not necessarily the color green. Green refers to the partially decomposed nature of the compost. Green compost may still have identifiable organic matter such as thicker stems or twigs or other larger pieces.
Fewer and fewer gardeners and landscapers are using inorganic mulches. The professionals have found over the years that these inorganic mulch products create more problems than they solve in the long run. There are times and places where an inorganic mulch may be useful in a short term temporary situation. Using black or clear plastic to solarize garden soil is one example. In some specialized landscape designs, gravel or rock mulch may be a fine choice when doing a xeriscape design.
One problem with inorganic mulches is their tendency to raise soil temperatures rather than lower them. Higher temperatures can stress plants rapidly and lead to disease, pest, and eventually plant death. Non-permeable inorganic mulch system can also trap gases such as CO2 in the ground, reducing the amount of oxygen available to the plant roots. These types of mulches can keep earthworms from reaching the surface (yes earthworms have to come to the surface to remain healthy). Environmentally, these types of mulch can be a disaster. As the plastic suffers from UV damage, it becomes brittle, breaks apart and is then almost impossible to remove from the soil.
Types of Inorganic Mulch
Ground-up used tires, glass beads and rocks are often used as mulches. We advise against using ground-up rubber tires as mulch in your garden or landscape. The rubber in tires is a petroleum product and contains an array of chemicals to prevent UV destruction, to make the rubber wear better and to prevent rot and decay. There are no materials in the ground-up tires that you want in your ground or around your plants. Glass beads are an interesting decorative touch in small areas. Widespread use is discouraged as they are fragile and as they age and decay, can shatter with disastrous results.
Rock and gravel are probably the best alternatives when used in a xeriscape landscape design. They raise the heat index in the garden and landscape, which can make the areas in which they are used several degrees hotter than the surrounding areas. They also tend to absorb heat and release it back at night, keeping your plants warmer then they prefer which can lead to plant stress.
A living mulch is a cover crop planted to protect the surface of the soil, to help with erosion, increase beneficial insects and to build soil health by keeping living roots in the soil year-round. Many cover crops that can serve as living mulches are also nitrogen fixers. These plants, when allowed to compost into the soil, bring nitrogen to the surface where it is more readily available. Living mulches are most often used in orchards and vineyards. We often plant a living mulch in our garden beds to keep them filled with live plants and active roots when we are letting a bed layout. One of our favorites is beets. We plant them extremely close together and let them grow all winter. The density of the planting keeps the beet fruit from developing fully, but the large healthy above-ground leaf structure shades the ground.
Organic mulches are vastly superior to inorganic mulches and should be your choice. Whether you choose commercially available products, locally produced native mulch or decide on a living mulch is up to you. There are times and places where one option is more viable than another.
The important thing is that you do mulch. In the long run, it will enhance the quality of your garden and landscape. Mulching is perhaps the single best thing you can do to build a healthy soil biome over the long run.