Cover crops in the home garden

Cover crops are an essential tool in sustainable agricultural systems, especially in organic or regenerative systems like we have operating at Diggers for our seed production and trials.

Cover crops vs. green manures

Unlike a green manure, which is tilled back into the soil, a cover crop is simply cut back, allowing the roots to remain in situ in the soil and decompose over time. Our winter and summer mixed species cover cropping systems, usually between four and six species, provide a constant living cover over the soil. This facilitates thousands of exchanges within the root zone, whereby the plants exude various compounds in a symbiotic relationship with soil microbiology (fungi and bacteria) – a relationship that involves the transport, conversion and cycling of nutrients.

We also use our cover crops as a natural weed suppressor, eliminating the potential for soil erosion and generating significant biomass that forms a mulch (crop residue) over the soil surface when cut back. This residue assists in water retention and infiltration, as well as managing soil temperature – things that are critical through the heat of summer.

But cover crops aren’t just a living mulch. Certain crop species are able to remediate soils of contaminants, behave as a biofumigant for potential soil pathogens, and can scavenge or bio-accumulate nutrients from deeper soil layers, making those nutrients available for subsequent crops. Legumes also have the benefit of fixing atmospheric nitrogen onto nodules on their roots, which builds fertility.

How to use a cover crop in the home garden

Whilst the best way to use a cover crop is to broadcast sow the seed in a bed that would be rested or left fallow between crops or between seasons, as part of a crop rotation process. When we are talking about a home garden, often space is a limiting factor for systems like crop rotations, which require enough beds to allow some to be ‘rested’ without a crop.

In our Diggers seed production garden, we are trialling a ‘crop phase’ option, where we squeeze multiple crops into one bed concurrently or relay them one after another with a clear crossover period. A cover crop can also fill the gaps as an ‘in between’ crop, either between the crop rows or in the pathways between beds.

Some of the following options can be easily adapted into the home garden.

Intercropping

This practice is akin to the principles of companion planting whereby a combination of crops is mutually beneficial. An example of successful intercropping we have used is broad beans/flax/wheat. It has been documented that flax has benefits in reducing fungal disease in pulse crops and improves the capacity for legumes to fix nitrogen. This in turn promotes faster biomass production from wheat, allowing us to grow our own mulch. Wheat can also develop a deeper root system, bringing nutrients up to the surface and making them available for the relatively fast harvest crop of the radishes, which are also a fantastic nutrient scavenger. This system can prevent the leaching of nutrients from the soil, as the plant mass accumulates nutrients within their tissue.

Each crop combination makes use of the entire physical space, filling in gaps and maximising production in what can be a small area, especially for the home gardener. Given that we are primarily growing for seed, the root system of the harvested crop will stay in place and the entire plant becomes surface residue when it has finished. We grow other species like red clover, lucerne and oats between our cropping rows, essentially growing a cover crop and a production crop concurrently.

Relay cropping

This is the practice of planting out new crops before the previous crop has finished. As we grow our crops for seed, our production season is extended beyond that of a fruit or root harvest, so relaying is critical for us.

One successful example we have implemented was the overlap cropping of our purple podded peas and tomatoes. Peas, being a legume, will fix atmospheric nitrogen over their growing season into the root zone so around three to five weeks before the pea crop finished, the tomato seedlings were planted into the standing pea crop.

When the peas were finished and harvested the crop was cut back, providing a thick pea straw mulch around the newly established and thriving tomato seedlings, which were benefiting from the fixed nitrogen in the soil from the pea roots at the best possible time, their early vegetative stage. Between the tomato trellis rows we sowed buckwheat (great at bio-accumulating elements like iron), brown mustard (which acts as a soil biofumigant to reduce root and soil pathogens) and millet (to generate biomass for mulch and suppress weeds). Mixed combinations of species in these planting phases means we create a diversity of root exudates, which will assist in supporting a diverse population of soil biology. It’s a perfect opportunity for the home gardener to easily and continually improve their soil.

Written by Jason Buchanan, Diggers trials and production.