THE DEEP COMPOST MULCH SYSTEM

The deep compost mulch system has been most used and promoted by many well-known farmers in the no-till farming space. Jesse Frost of Rough Draft Farmstead and the No-Till Podcast, Richard Perkins of Ridgedale Farm in Sweden (author of Regenerative Agriculture), and Josh Sattin of Sattin Hill Farm have all provided fantastic models of successfully implementing this system on small-scale commercial farms. The deep compost mulch system could be categorized as no-till, lasagna gardening, or no-dig. The no-dig term was primarily developed and spearheaded by the well-known organic gardener Charles Dowding.

What is Mulch?

Mulch is a term referring to anything used to cover the ground, whether it be woodchips, plastic tarps, landscape fabric, compost, or other materials. Covering the ground (a key principle in the no-till approach) protects it from the elements, retains moisture, fosters living soil, maintains carbon, and suppresses weeds.

In the deep compost mulch system, the compost itself serves as the mulch. In this system, the first four to six inches of compost are layered above the native ground, and the first crops are planted directly into this compost. The compost serves as the growing medium while also doubling as the mulch, holding in moisture and encouraging the soil biology. 

When building beds with this system it’s recommended that you first level the ground, test the soil, add needed amendments, ensure drainage is good, and adjust accordingly. Ideally, you would then tarp the space with a silage tarp for as long as needed, allowing all surface material to decompose and all weed seed in the surface to germinate and then die. Then you would lay out cardboard (free of tape, staples, or any other contaminants,). Then finally you would layer on 4-6” of compost for the beds, and woodchips for the pathways and borders. Note: I’ll go over this process in detail in a separate article coming soon.

One of the main pros of deep compost mulch is weed control. While it’s not 100% foolproof in preventing weeds, it prevents most annual weed seeds from successfully germinating by burying and suppressing them. 

Another pro is how quickly the deep compost mulch system allows you to start growing on your farm. With such a deep layer of compost, the plants will not be very affected by any imbalances in the native soil below. It’s still best to balance and amend the native soil initially, but you don’t have to be completely reliant on it to grow good crops right out of the gate–a huge plus!

If you have heavy compaction, start by making a pass with a broadfork to loosen and aerate. After layering on a deep layer of compost mulch, you will be able to plant right away. The roots of the crops you grow will continue loosening the soil over time, as the nutrient-rich compost above works its way down.

This system is also hugely beneficial for soils suffering from low organic material. Adding a high volume of compost like this will quickly raise your percentage of organic matter.

While it may sound superficial, having pure black compost covering your garden beds creates a beautiful aesthetic. Having a nice-looking farm with dark, vibrant soil comes with many advantages. It’s great for marketing. Whether it’s attracting visitors to tour your farm, or having pictures you can post on social media or your website, having beautiful beds can increase interest and demand for your product.

There are also some cons to the deep mulch compost system. The first would be the availability and quality of compost you have access to. Many farmers struggle with not having access to quality compost in their local area. This system may not work for your context if you can’t find consistent, high-quality, local sources. Local landscape companies and municipalities are good places to start looking. 

The other con to this system is the cost of the compost. You have to buy a lot of material to make this work. While it can be a significant upfront expense, the long-term benefits should prove to be a good investment in your soil. If coming up with cash is too much of a barrier, it goes back to the trading time versus money concept. Without the money to invest upfront, the alternative is planting cover crops and creating your own compost. You can get there eventually, but the time investment before startup will be higher.

The next con would be labor. While building these beds takes a lot of work, there are some ways to mechanize it if you have a front loader, compost spreader, or a friend you can borrow one from. On a small scale, wheelbarrows and five-gallon buckets will suffice. Regardless, it still requires a lot of energy to build beds this way. Organizing a group of friends and neighbors to help out for a “bed building day” is a great way to kick start your deep compost mulch growing space. 

When you layer a high volume of loose fluffy compost onto the ground, it’s essential to factor in erosion risk. Until the crops have had a chance to get established and hold the soil together with their root systems, an extreme rain event could wash away a lot of high-value compost. This can be devastating!

One method of preventing this is to avoid building beds during rainy seasons and keep a close eye on the weather forecast. The other more foolproof method is to grow under caterpillar tunnels or high tunnels. With extreme weather events seemingly becoming more common, growing under tunnels can give farmers great peace of mind that their soil and crops will not be destroyed.

Keeping your compost pile covered with a tarp protects one of your most valuable assets on the farm. Heavy rainstorms can wash away a lot of compost, so keeping it covered is a must.

When determining compost quality, you need to look at it, feel it, and smell it. While the dark color and consistency are a part of the criteria, the smell is even more important. If it smells like ammonia, manure, or any other unpleasant way…something is off! It should have a pleasing earthy smell, like after the rain. Follow your nose!

Asking other local growers is a great place to start when trying to find a good source of quality local compost. Learning from their direct experience is helpful before you make your investment in a product.

If unfinished compost is all that is available to you, one option is to buy it and finish composting it yourself. This will require extra time and effort, like checking the temperature, watering it, and turning it. This is not the ideal scenario, but it may be worth considering if it’s your only option.

Another thing to check for when purchasing compost is weed seed. If the facility you’re buying from is not getting their compost hot enough, weed seed can survive and then find its way into your beds. Remember, the point of the deep compost mulch system is to smother weeds and reduce the need for cultivation. Compost with weed seed would defeat this purpose.

Residual pesticides and herbicides in materials used to make the compost are something to check for when purchasing your compost. Ask the facility where their sources come from to ensure it doesn’t contain potential contaminants. It can take a long time to remediate contaminated fields and put them out of production for a significant period of time.

Compost is most commonly applied at a much lower rate than in the deep compost mulch system. It’s typically spread over beds at just 1/2-1” thick and then incorporated into the topsoil with a tilther or a shallow till. When added in such small amounts, the compost adds fertility but not very much organic material.

In the deep compost mulch system, using 100% pure nutritional compost can actually be too nutrient-dense for optimal plant growth and even cause problems for your crops. Because of this, it’s recommended to find a mixture of compost and leaf mold (decomposed leaves). A mix that’s 50% compost and 50% leaf mold is ideal.

Leaf mold is an excellent source of carbon and very nutrient-dense. Composting leaves on your property (if available) is also a wonderful way to build up your soil. If you can’t find a local source that sells a leaf mold/compost blend, you can always purchase them separately and mix them yourself by adding a 1:1 ratio to your beds.

Now that you know the pros and the cons of this system, you can make an informed decision as to whether or not it’s the right fit for you and the context of your farm. While it can be quite an undertaking to start up, the long-term benefits are significant.

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