A different perspective on weeds in multi-species cover crops

By Angus Deans

I frequently witness applications of herbicides prior to multi-species cover crop sowing and find myself pondering the following question: Why kill weeds when preparing to sow a multi-species cover crop whose purpose is primarily to improve soil structure and stimulate soil microbial and animal life?

First let us explore what a herbicide is designed to do. Then we shall examine whether it really has a place in a regenerative system . A herbicide is designed to kill plant life. Some are broad spectrum and are designed to kill all they come in contact with. Some are designed to merely kill specific plant families e.g.: grasses, or broadleaved plants. All of them kill algae – the tiny plant life that is the very foundation upon which soil life is built.

So my question is – if we kill the ‘first step’ in a journey of a thousand miles – will we ever reach our desired destination? I think not.

It is important to return to the reason we had for considering planting a multi-species crop in the first place. Was it a tax problem that meant we really needed to spend quite large sums of money very quickly? Or was it that management has reduced the ability of our soil to support a thriving biodiverse flora? Flora that is actively feeding all of our soil life and our animals if we are grazers, or our crops if we are croppers.

Most typically it seems to be the latter, and we are looking for a way to stimulate life in our soil in order to increase our productivity and resilience of production. So, do we really believe we can achieve this by participating in a practice that is designed to kill the very foundation upon which we are trying to build?

Here is the challenge. Many of us now have an understanding that weeds are trying to heal the landscape in which they are growing. Some weeds are:-

• actively addressing physical soil structure mechanically,

• accumulating minerals to make them available in biological form for supporting higher order plant and animal life,

• acting as sponges to prevent mineral leaching, and sometimes to convert them into less harmful forms,

• actively involved in even more than one of these processes!

And they are all doing it for free.

But we do not want those nasty weeds, they have become the enemy. We want something that is more desirable to our neighbours and our peers, and maybe more palatable to our livestock. However, if the weeds we are experiencing are low in the order of successional plants then we need to listen to what they are telling us about the state of the health of our soil. We cannot merely insert seeds of plants that are designed to grow in a soil of Ferrari style performance when our soil is actually functioning at the speed of a Model T Ford, and expect amazing performance.

That does not mean we should not try to grow that multi species crop for we are intending to build biodiversity and performance at a faster rate than Mother Nature does. After all we have debt and financial commitments to honour.

Let’s imagine that we are planting a multi-species planting of 10 species for example, and that our soil has 4 weed species growing. If we plant into the weeds we now have a more diverse planting of 14 species – 4 of which we have achieved for free. And we all know that biodiversity is what we are aiming for.

But…some will say – those weeds are not palatable to my livestock, or will take over and suppress everything else, or will take all the moisture. If that is the case, then think back to the stage of development that your soil is currently in and what your weeds are indicating.

Ways to shift soils away from weed dominance:

1. Identify what your weeds are indicating

2. Target the root cause e.g. super compacted soils? Add in a gypsum with the seed. Bacterial domination? Add in a complex food like humates…

3. Improve cover crop vigour by adding dried vermicast or seaweed down the drill with the seed

4. Embrace weeds as added diversity and benefits

Would you rather have those weeds actively working as part of your team that is aiming to move your soil health in the direction you desire? Or would you rather herbicide them and keep your soil exactly where it is at – travelling at the speed of a Model T instead of a Ferrari

By Angus Deans