What Is Compost?
What is compost? Compost is wood waste in the final stages of the decomposition process. Wood becomes mulch, mulch becomes compost, and compost becomes humus in the soil. The end goal for plant nutrition is always humus. We will go more into depth on humus another time but just know that is the currency of the soil that microbes depend on when feeding your plants.
Properly made compost is a gardener’s best friend. Unfortunately, most commercially available compost is made incorrectly. Using low quality compost causes many of the problems we find in trees and landscapes. We went around to the more popular compost producers in Houston, at our own expense and tested them in our own ArborTrue Lab, at AgriLife, and at Environment Celebration Institute. The ArborTrue Lab utilizes the finest in molecular biology with DNA extraction. This allows us to detect hard to find pathogens at the molecular level without needing to culture the samples.
High Quality Compost:
- Takes 2-3 years to make
- Is made from small twigs and leaves, vegetables, and sometimes horse manure may be added.
- Will be kept sufficiently wet through the process
- Is heavy due to mineral density
- Results in mineral dense, fungal populated, biologically active material
- 100 yards of fresh woody waste will only yield 10 yards of compost due to the carbon gassing off as CO2
- Produces explosive growth and healthy plants
Poor Quality Compost
- Is often sold after only 6-12 weeks
- Is made from almost any wood waste including pallets and railroad ties with toxic levels of heavy metals, tree bark, trunks, and plastic or other trash.
- Moisture content is not adequately monitored
- Is filled with weed seeds due to inadequate “cooking” time
- Is often lighter in weight doe to excess carbon content and limited mineral density
- Is limited in biological activity due to inadequate time composting, sterilizing treated wood ingredients, and will almost never have beneficial fungus.
- 100 yards of fresh woody waste will yield 30-90 yards of inferior product
- Will make plants sick and possibly kill them. Makes the soil toxic and creates long term plant problems. Is toxic to handle with bare hands.
Attached are some compost samples we took from a few locations in the Houston area. The only sample that we have permission to identify is Sample #1, Natures Way Resources. If we get permission to share the others, we will make those visible as well. Notice that the nutrient content is much higher on Sample 1 compared to the others, both nitrogen and especially the mineral content. Also note that the fungal counts do not exist on any of the other samples because those piles were turned over too many times too quickly in a short period of time. Natures Way static piles their compost so it takes longer but the end product is starkly better in comparison.
Compost that is produced too quickly will have weed seeds. If you spread it in your flower beds or lawn you will grow whatever is in the compost, including invasive plants and trees. Compost must go through “hot cycles” where the heat from the energy release is long term enough to kill viable seeds (same for disease spores).
Compost made from environmental waste such as railroad ties and treated pallets will have exceedingly high levels of heavy metals. These heavy metals are often what cause plants to turn yellow with strange discoloration patterns. They will look like they are starved for iron, but you may notice that adding iron either does nothing or only temporarily improves plant appearance. Zinc and Copper are commonly used to prevent microbial growth in construction materials like treated lumber and roofing shingles.
Carbon to Nitrogen ratios:
Compost is made from wood waste. Wood waste is high in Carbon and low in Nitrogen. Trees make up the majority of wood waste at compost and mulch yards. Trees make carbon dense trunks to compete for sunlight because carbon is light and very strong. This means that the tree may have a Carbon to Nitrogen ratio as disproportionate as 700:1 with the most common being around 500:1 depending on which part of the tree is used. Bark is commonly 700:1 while pulpwood is 400:1 and leaves and twigs are closer to 200:1. During the process of decomposition, the carbon gasses off in the form of Carbon Dioxide while leaving mineralized Nitrogen behind. This reduces the presence of Carbon and therefore the size of the pile shrinks. The longer the compost sits, the less carbon and material will exist. This is why quality compost appears so expensive, its simply more concentrated.
Bacteria to Fungus ratio:
Compost that is rapidly made will only have bacteria in it. Bacteria are great (usually), but this presents an unnatural balance. When the compost is turned constantly the carbon gasses off and the C:N ration may be ok, but no beneficial fungi were able to grow with the constant disturbances. It is important to have beneficial fungi in compost as they are much more stabile and the bacteria are not, they can rapidly die off and be replaced with pathogens. Beneficial fungi are essential in healthy soils.
Compost produced quickly will not stay hot enough for long enough to destroy pathogens. Keep in mind that most compost is made from trees that were trimmed or cut down. Why do people cut down trees? Well at ArborTrue we can confidently say that most of the time the tree is diseased. Mulch and compost yards receive deadly diseases every single day at their locations. If not aged properly, those diseases are spread around the city in the form of unfinished mulches and composts. We use PCR (polymerase chain reaction) technology to look for these diseases at the molecular level. The tests are highly accurate. Most places tested positive for one or more common diseases.
Finished compost should never smell sour. That sour smell comes from bacteria and yeasts that are converting carbohydrates to alcohols. This smell has been confused as indicating quality but that is far from the truth. Finish compost should simply smell earthy. You cannot smell quality compost from a mile away like you can with unfinished compost. You do not have to be a scientist to know the difference!
Finished quality compost will be dark, nearly black. When wet it will probably look solid black. Some places will dye mulches and composts black in order to look nicer. They do so with carcinogenic toxic materials like dust from coal fired power plants or by using toxic alkaline chemicals like Carbon Black from the petrochemical industry. These are environmental waste products that are perfectly legal in the state of Texas to dump in wood waste and sell directly to uninformed customers.
Shape and Size:
Compost can come in many shapes and chip size. It should never have perfectly geometric shaped wood chips that clearly just went through a wood chipper. Only junk products look like that. Once aged properly, compost will be screened through a barrel screener that separates larger chunks from smaller pieces. Ultra-fine screened compost is commonly used for turf grass applications since it will fall between the grass blades without smothering the grass. Larger 3/8” screened compost is most popular for beds but ½” screen is just fine as well. As a rule, the larger the screen, the longer the compost will last and the more fungi it will attract in the soil. When we male our own compost for soil amendments, we commonly use a 1” compost for soil structure. This I not commonly available in the commercial market due to a lack of knowledge and market. NEVER purchase dyed product.
Tree Care Topic:
Dec 22, 2020