Cover Crops (Study Notes #1)
- Maya Carroll Tischler
- Feb 25
- 7 min read
Cover cropping is a method of soil restoration, which follows a seasonal pattern of regeneration. By working with plants specific to the soil needs, growers can increase the available nutrients, capture carbon in the soil, feed the soil biology (critters) and fight erosion.
"If we observe Nature, we see very rapidly that she abhors a vacuum. If land is cleared she will cover that bare soil as rapidly as possible. There will not be one weed, but a diversity of pioneer plant life that fills the gap."
An exert from:
More and more as I'm gardening and farming I'm starting to hear both sides of the conversation and really sink into true observation. Instead of seeing an issue like an overgrowth of sheep sorrel, I hear the land saying "hey look this patch is compressed and the soil needs love!" This, as well as working on a local farm on a larger scale than I'm used to, has got me thinking about cover crops.
Here's my notes so far, really just covering what cover crops are and why they can be beneficial. I hope to dig deeper as I learn but for now, I hope you find these useful!
Cover crops work with a variety of plants to suit a variety of circumstances.
Generally the methods used to cover crop will change within a sliding scale of time and size.
Cover cropping vs Intercropping:
Intercropping: Either annually by planting the cover crop at the same time as the cash crop, growers are often fearful of losing realestate for the cash crop but within certain examples, especially those Intercrops which increase nutrients like nitrogen, cash crop yields actually increase.
Or perennially by creating patches of ongoing cover crop - could be useful on a slope, perennially would probably deliver most soil and biomass benefits. Some growers design belts of biomass plants for an internal mulching system.
Cover cropping: For whole areas from larger scale fields to small scale garden beds, planted and terminated before the cash crop is planted. This is more efficient for space and machine use, as well as still providing most other benefits.
To begin I've considered some common reasons cover crops are used:
Decrease damage from erosion: Strong rain, sun and wind will cause soils to erode, this might be physically, like the banks of a river bed where soil is swept away or nutritional leaching, where water pulls nutrients out of the soil as it passes through it and this follows the general guideline that fertility goes where water goes (often downhill.) The roots of the cover crop, as well as the above ground 'living mulch' slows the water down, protects the topsoil from wind and sun and physically add structure to the soil, fortifying it.
Decrease evaporation: Typically soil doesn't want to be exposed to the sun, so for all the reasons listed above a cover crop can hold precious moisture in the soil.
Condition the soil in preparation for growing: Cover Crops are often used as part of a cycle where the land is then planted with the cash crop, either after the cover crop has died or intercropping where both are planted at the same time. The crop being cultivated will impact which cover crop is used for it's unique abilities to compliment the specific needs of the chosen cash crop. I've always felt like it's a bit of a trick question, how do I prepare the soil for planting plants in it? Plant plants in it!
Increase the biodiversity in the soil: Cover crops work on many levels to increase the biodiversity in the soil adding fungi which they often have symbiotic relationships with, beneficial bacteria, microbes and providing the right conditions for all kinds of critters. Soil biodiversity is almost always a positive and it directly impacts the quality and health of the chosen crop. Soil nutrition = plant nutrition = Human nutrition.
Increase the Nutrition available in the soil: Of course inextricably linked with the biological biodiversity mentioned above, cover crops also work on a chemical level, with different cover crops making different nutrients more plant-available. Nitrogen, calcium and phosphorus are often mentioned but certain cover crops can even mine minerals from deeper in the soil bringing them up to the top of the soil, making them plant-available.
Carbon sinking: Through trapping carbon both in the roots and the above ground plant - all of which hopefully gets returned to the soil and increases the overall held carbon as well as the physical structure of the hummus.
Soil Pest Control: Some cover crops are bio-fumigants, such as brassicas, which can be used to decrease diseases and pathogens in the soil. -Although to note that these can also lack some of the beneficial fungi relationships and may decrease inoculation if thats a soil goal.
General Biodiversity: Cover crops increase the variety and can provide habitat and food for above ground biodiversity too! Like flowers for bees.
Notes on small scale cover cropping (or not):
For smaller market-garden style farms it's likely that a mosaic approach will be taken to managing the soil health with mulch, manure, fertilisers like seaweed and weed tea, living mulch, perennials and compost being added. For many gardens cover cropping may not be necessary at all but it is a useful tool to keep in your back pocket. In a smaller context there's a fair bit of overlap with similar techniques like 'chop and drop' I belief the integration of all relevant practices (using the extra care that can be taken with smaller farms and gardens) offers more richness, complexity and resilience.
There is a cost saving angle compared with other forms of soil conditioning like expensive manures or fertilisers as well as saving costs on weed management - planting a thick cover crop can help outcompete unwanted plants in a bed.
Could be used to kick start a new garden bed!
NO BARE SOIL EVER!
In my ideal world I would get to a point where I intuitively know when to plant each crop and manage a selection of annual and perennial cover crops within that structure following a kind of rotating mosaic so that no area is bare for two long.
The never ending quest for biomass:
The addition of biomass and nutrition, is important for the longevity and sustainability of production. The climate is the biggest factor here for creating your own biomass, I am managing a cool climate farm and have had to work with seasons of dormancy. A tropical food forest is a good example of high turn over biomass with plants putting on more steady growth. - Although I'm excited to work within my climate parameters and imagine that I can take advantage of my pruning seasons to increase the biomass on the ground.
"They generate a lot of potential green waste that can be clipped or pruned regularly to add mulch to the soil surface. In using this method, you’re essentially replicating what Mother Nature does in a lush forest. As leaves and branches drop in a forest, they break down and create a thick, spongy layer of compost.
By mimicking this system in your space, you are essentially producing your own mulch and compost right on site, rather than needing to bring it in from elsewhere."
An exert from:
Thinking like a farm (Intercropping for succession):
My biggest light bulb moment happened late last year when I realised you can't just plant the same plants as a mature food forest farm and expect succession to happen!
You have to plant relevant plants within a timeline, ie: plant choices will be different for a new farm vs an established farm. It's better to speed up succession and increase fertility within the frame work of the larger plants, by starting with plants that are quick to cycle back into the soil.
My example is that on my cool climate farm we have planted a large amount of Tagasaste (Tree Lucerne) but Tagasaste is going to need time to grow before it can me chopped back in, so now my next mission is to plant 200 Comfrey plants for a quicker chop and drop. This part of my succession plan I would describe as intercropping because we have these - almost rice paddy like terraces and on the slopes between the terraces I'll be implementing my biomass, fertility-boosting intercrops. Use the edges and value the margins folks! I know I'm a permaculture cliche, at least I resisted building a herb spiral.
Plant types common to small scale cover cropping:
Peas, Beans, any legume for nitrogen fixing
Sorghum
Buckwheat
Chard or Silverbeet
Any root crop to reverse soil compaction
Nasturtiums
Mustard greens
Plant types common to small scale intercropping:
Comfrey
Flax
Rhubarb
Yarrow
Sorghum
Elderberry
A farm's area of influence, wholistic outputs:
Wholistic outputs is a regenerative theory I'm working on to describe the outputs beyond crop production and sellable product. What if, for instance, the water leaving the farm is actually cleaner and has more mineral content than the water being used on the farm, or entering the farm. What if we can increase animal and insect biodiversity in the general area around the farm. Or actually have secondary agricultural products being sold into the local area like: Compost, Garden Teas, Biodynamic preparations that generally add fertility to the local area.
These are my notes so far, I'm excited to implement more cover crops both in the margins of the slopes with my perennial intercropping and on the low-till terraces with soil building annuals. This really just covered the tip of the iceberg, considering what cover crops are and how they're used, hopefully next time I touch on cover crops in my study notes it will be a 'How to cover crop', covering methods of implementing them, from sowing to terminating to the best times to chop and drop.
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