OrBio – a Cover Crop Strategy for Market Gardens

A bug’s eye view of the sky, from a stand of cover crop
Photo © Craig Mackintosh

A recent post by Australian permaculture aid worker, Miles Durand, writing from Lesotho, reminded me to share a method of growing vegetable crops alongside cover crops that I learned when I studied organic biological horticulture many years ago. In the context of the holistic soil science and natural pest control studies I was then immersed in, this method seemed a logical outflow of the principles contained therein, and yet I don’t think I’ve seen anyone using this method in permaculture, or, indeed, even other agricultural circles I’ve come across. Some of you may wish to give it a try!

The name of the system I will outline was presented to me with the acronym ‘OrBio’ — short for Organic Biological, with the cyclic inference of the word ‘OrBio’ also representing a key aspect of the system, as you shall see.

I’m going to ‘take as read’ that readers are already familiar with the benefits of cover crops (otherwise known as ‘green manures’), and for those who are not, you might want to head here first, before returning to this page.

The OrBio system, which I will briefly outline below, is most suited for those with market garden-sized areas of land, or, it could be implemented as a part of a small or even larger farm context. This system would also be an excellent transitional approach to take for farmers seeking to move from a monocrop-based system to a healthier, more diverse system, whilst still utilising the mechanisation (rototillers, for example) that they may have come to depend on in the current economic context.

So, on to how it works….

Imagine you have a 50 x 50 metre section of land, for example, to utilise for growing vegetables. The normal approach is to lay seeds and seedlings out along rows that would be 50 metres long, and about 50 centimetres apart. In a market garden scenario, these rows might be prepared with a rototiller, and the seed and seedlings then put into place.

Now, please imagine that, instead of having your vegetable rows 50 centimetres apart, you instead make them about 1 metre apart — and in between these vegetable rows, you seed a cover crop mix that is about 50cms wide.

You would now have alternating 50cm rows of vegetables, cover crop, vegetables, cover crop, and so on. The exact width of these rows would be largely determined by the kind of vegetables you wish to plant, and whatever mechanised equipment you may use — like a rototiller, or a hand-powered seed disperser for seeding the cover crop, like the one pictured below, for example.

The cover crop would ideally be a mix of four or more plants — a couple of grasses, like rye, oats, wheat and barley, for carbon, and a couple of legumes, like vetch, red clover, cow pea, etc., for nitrogen.

Before I continue outlining an additional stage to this system, I’ll mention the obvious implication for it — that you’ll now be using twice as much land for the same amount of vegetable crop. But, before you throw the baby out with the bath water, the following key benefits need to be taken into this accounting:

• Weed suppression — your cover crop mix will grow fast, and help smother out other weeds which are usually much tougher to deal with than the easy-to-manage type of plants mentioned above.
• In-situ mulch — when the cover crop reaches the height limit you do not wish it to breach (i.e. when it starts to shade out your crop), it can be cut (ideally with a scythe — which, when used correctly, can be very efficient) and laid down (or just pushed into place with your boots) as mulch around the vegetables growing right next to the cover crop rows. This mulch, growing right where you need it, helps to feed the soil (providing carbon and nitrogen for the microbial life that are in turn feeding your vegetables) and provides extra weed suppression right on your vegetable rows.
• Moisture retention — a covered (and mulched) soil retains significantly more moisture than a bare soil, and so requires less irrigation. In addition, the cover crop foliage can create a more humid above-ground micro-climate for the adjacent vegetable crops.
• Soil retention — the cover crops make soil erosion from wind and water virtually non-existent.
• Soil development — as the cover crop grows, their roots penetrate into the soil. Some cover crop plants, like the red clover I mentioned above, for example, have deeply penetrating and also good laterally-developing root systems. This means when the red clover reaches the desired height, and is cut back, that these expansive root systems die off and get converted into carbon-rich humus, and leave aeration channels and healthy soil aggregates in their wake, after having first brought nutrients and minerals up from depths many vegetables cannot reach. Compaction is thus minimised and a healthy soil structure can be achieved — a sponge-like structure that’s also amenable to the upward draw of water through capillary action — as well as translating to less problems with compaction-loving ‘pioneers’ (i.e. tough, prickly weeds).
• In-situ predatory insect habitat — the alternating cover crop rows become habitat for beneficial predatory insects, conveniently placed right next to your vulnerable vegetables. (In the case of flowering clovers and the like, they also provide food for pollinators.)
• Insect distraction — these alternating cover crop rows in themselves are a big distracter for pest insects, making your vegetables more difficult to locate in the first place.

But wait, there’s more….

Now, on to the ‘cyclic’ aspect of the OrBio system. After your season ends, and you’ve (hopefully) harvested a nice crop of vegetables, you need to plan for the following year. You need to ensure your alternating rows are clearly marked out with stakes, as next Spring you will ‘swap’ your alternate rows — you’ll plant your cover crop where your vegetables were, and your vegetables will go where your cover crop was.

In short, it’s like you are picking the whole layout up, and moving it one row over.

The obvious benefit here is that your vegetables are now growing in an enriched soil, with an improved structure, and the cover crop is growing in the strips that have been somewhat depleted by the nutrient uptake of your harvested vegetables.

Traditionally, farmers learned (thousands of years ago) to rotate their crops at regular intervals. They would grow a field of a particular crop, or crop mix, and then after a few years, or several, they’d leave that land to rest, and they’d rotate to another area. This gives the soil opportunity to replenish itself through the growth and decay of other plants, and breaks up cycles of disease that may have developed in the soil. The OrBio system is similar, but done annually, and on the same piece of land — but whilst integrating in-situ weed suppression, beneficial insect habitat, and all the other benefits mentioned above.

Other thoughts

The above is a broad outline of the concept. It is impossible to get into specific details, due to the variance of climate and soil types that our worldwide readership embodies. But I will mention a couple of points to take into account.

One is timing. Cover crops generally grow faster than most vegetables. You’ll normally want to give your vegetables a good head start, by getting them in three or four weeks before you plant your cover crop. As such, you will likely need to utilise the very efficient wheel-hoe (inset, at right), or use a rototiller to a shallow depth, to disturb upcoming weeds immediately prior to planting your cover crop seed.

The other is where to walk! Cover crops in general are more sensitive to being trodden on than your hardy pioneer weeds. Once established, your cover crops will handle a little trampling without much trouble, but in the interim you’ll want to keep your feet within a narrow border between your vegetable and cover crop rows.

And, finally, I reemphasise that this can be an excellent way to transition from a more mechanised system, to one less so. The smaller scale, back-yard permaculturist can make use of raised beds (or sunken beds in arid climates) to have an almost completely no-till system. But, for the existing market gardener, who must balance outputs against the inputs of human labour, this system allows for a semi-mechanised option that, with the right combination of plants and timing, can allow for efficient planting, maintenance and harvesting to maintain profitability, whilst building soil, reducing irrigation costs and shrinking issues with pests and plant disease.

Instead of an entire Midwest, for example, covered in a monoscape of inedible genetically modified corn that’s steadily depleting its soil bank, I like to envision a patchwork of smaller-scaled, diverse, market gardens — with increasing diversity in above- and below-ground life, and intersected with a multitude of Zone 5 ‘bio-corridors’. Such a scenario would not only restore eco-system services and climate stability, it would also allow more land-based employment and with it the re-emergence of community, and economic stability. An approach like this is worth considering for those in a position to implement it towards that end.

And, for the back-yard permie who may be intrigued by this idea — consider that there’s nothing to stop you from growing some cover crops on the sides of your raised beds!

Tip: One tool that, at this scale, can be very useful for Springtime soil preparation is the broadfork. A broadfork is a wide, two-handled fork that makes it very easy to aerate and break up soil compaction — using your own body weight to do much of the work. See one version of the broadfork in use here. The video I just linked to is a straight-tine version, but you can also get (as I have) a curved tine model, like the one pictured at right, which makes an already easy task even easier, through the increased leveraging you get with the curve in the upper part of the tines (the curves grant a pivoting effect as you pull back on the handles). With a broadfork, you can easily cover a lot of ground in a single day, with no fuel required, beyond a hearty breakfast.

Cover crop resources:

• Cover Crops Solutions Chart
• Green Manure Resources