Compost - You Know That's Right
The use of compost is a foundational practice in organic growing. Compost adds organic matter and beneficial biology to the soil, both of which ensure the availability of essential nutrients to plants. Compost is also a recycled input; when we apply compost we are taking what was once waste or excess and adding it back to the soil in a form that is beneficial to our crops. In vegetable production, we are removing organic matter in the form of crops but by adding compost to our soils we are replenishing what we have removed. So, compost is a good thing, but, naturally, there is such a thing as too much compost... we'll get to this in a bit.
The benefits of compost are best realized when a high-quality compost is used. Making compost can be a highly rewarding part of farming or gardening, and we recommend keeping a compost pile (or three) to anyone who it growing their own produce. Many highly successful farms and gardens put significant efforts into making compost, and for good reason. There are also many commercial and bulk composts available. If you are considering purchasing your compost, it is important to know the source ingredients and processes involved in creating that compost. Ideal composts contain a well-balanced blend of source materials (more = better). Well made compost will have maintained temperatures high enough to kill weed seeds and pathogens, and have had plenty of time for all components to decompose and mature. High-quality composts are stable and full of available nutrients and beneficial biology. Incomplete or unbalanced composts can have a negative impact on plants. Manures that are not fully composted may inhibit nutrient uptake or cause burn to plants. Raw manures may also contain pathogens. The bottom line is that not all composts are created equally.
Before purchasing and applying a commercial compost, we recommend asking for an analysis. If the provider doesn't have an analysis, then you really don't know what you're getting. Once you have that analysis, you can put those numbers into our compost calculator and see what the nutrient load of a given volume would be. It's easy to see that compost is a great source of nutrients, but that if it's over-applied it can quickly create excesses or imbalances in the soil.
In recent years, another challenge with composts containing manure has developed. A number of selective, persistent herbicides known as synthetic auxins (active ingredients Clopyralid, Aminopyralid, Aminocyclopyrachlor and Picloram) used to kill broadleaf weeds in hayfields and pastures has been shown to persist not only in treated hay or pastures but also in the manure of animals that consume the grasses from those fields. Unfortunately, these herbicides can remain toxic to plants (especially tomatoes, beans, cucumbers, lettuces and related species) for up to four years, even if the manure is well composted. Symptoms of persistent herbicide contamination appear as curled or distorted leaves, twisting stems and other deformations, and an overall lack of plant vigor. We regularly receive reports of persistent herbicide damage stemming from contaminated compost. If you are buying bulk (loose) compost, we strongly advise you to talk to the supplier and ask if they know whether any of these persistent herbicides have been used on the hay that was fed to any livestock that contributed manure to the compost.
If you believe that you do have contaminated compost in your soils, all is not lost. The first thing to understand is that these herbicides are only toxic to broadleaf plants - not grasses, insects, animals or people. The second thing to know is that contaminated soils can be remediated. The timeline for full remediation will depend on the amount of herbicide in your soil, as well as environmental conditions and the practices you implement to address the situation.
Soil biology will break down and consume the herbicide(s) over time. To accelerate this process, you can add beneficial biology with a concentrate like Mikrobs, Kenkashi, or another beneficial microbial complex, and you can add things to support and promote soil biology like molasses, kelp or alfalfa meal, or biologically-based fertilizers like feather or blood meal. Intact soil structures (minimal tillage), warm temperatures and good soil moisture also promote biological activity in the soil and will accelerate the decomposition of residual herbicides.
In addition, you can grow a high biomass grassy cover crop like millet or sorghum/sudan grass in summer, or rye or wheat in winter. These plants can bio-accumulate residual herbicides and help reduce the overall amount of herbicide remaining in the soil.
As we said at the beginning, compost is a foundational part of organic farming and gardening, it's just important to know your compost, and know it's right.