Cover crops and companion plants

A vineyard with cover crop between rows.

My last post dealt with underground fungi that form symbiotic relationships with grapevines. Today, I'm investigating cover crops and companion plants that can be grown with the vines to help promote healthy soil structure and nutrient exchange and perhaps even protect against insects and disease. Cover crops have been used for millennia and are becoming more popular again with the advent of organic farming and the desire to reduce the use of pesticides and herbicides.

Ribwort plantain

We've left the field around the vines natural, without destroying the weeds and grass. We've been cleaning an area around the vines to reduce overgrowth and competition with the vines and their roots. I've also been digging out the docks (Rumex obtusifolius L.) as I wrote about last year. Curiously, for some reason, I did not dig up another broad-leafed weed, the ribwort plantain. It is a common weed of cultivated land. I kept leaving it for another day. Plantago lanceolata is a species of flowering plant in the Plantaginaceae plantain family. It is known by the common names ribwort plantain, narrowleaf plantain, English plantain, ribleaf, and lamb's tongue.

Here I was reading along in the review paper I found online about AM fungi when I came across the section on cover crops. Turns out that the ribwort plantain is an exceptional cover crop to grow with grapevines. This plant can apparently influence the uptake of AM fungi by vine roots. The study cited indicates that encouraging plant diversity in vineyards can be valuable, provided that they do not compete for nutrients or water with grapevines.

Companion plants

Another plant suggested as a companion plant for vines is Tanacetum cinerariifolium, a perennial species of flowering plant in the aster family, Asteraceae, otherwise known as Dalmatian insect-flower. It looks like a daisy. The plant is a natural source of insecticide. The active components are pyrethrins, contained in the seed cases. Pyrethrins attack the nervous systems of all insects. When present in amounts less than those fatal to insects, they still appear to have an insect repellent effect and inhibit female mosquitoes from biting. They are harmful to fish but are far less toxic to mammals and birds than most synthetic insecticides. They are not persistent, being biodegradable, and also decompose on exposure to light. They are considered to be amongst the safest insecticides for use around food. I believe we may have it growing on our land naturally, although it is native to Croatia. Chrysanthemums are often used as companion plants to repel insects from nearby crops and ornamental plants.

Common vetch, Vicia sativa, is also considered an excellent companion plant for grapevines. It belongs to the Pea Family – Fabaceae (Leguminosae). It's a winter legume and grows as a wildflower here. In Roman times, bell beans were planted between the rows of vines, making good use of the space. Let's look at why we need cover crops.

Cover crops

Cover crops help winegrowers manage their soils in multiple ways. They help to:

• IMPROVE SOIL FERTILITY, increasing nitrogen and cation exchange capacity when decomposing
• IMPROVE SOIL STRUCTURE, decomposing roots leave voids in the soil reducing density and helping air and water penetrate into the soil, thereby increasing water retention
• REGULATE VINE GROWTH, both invigorating and competing for nutrients, which reduces the susceptibility to grey mold and downy mildew.
• PROTECT SOIL FROM EROSION, binding its surface with their root systems
• PROMOTE BIOLOGICAL DIVERSITY IN THE ROOT ZONE, as organic matter is a food source for macro- and micro-organisms. 
• PROVIDE HABITAT FOR BENEFICIAL INSECTS & ARACHNIDS, beneficial arthropods (spiders and mites), in close proximity to the vineyard, control harmful insects 
• IMPROVE AIR & WATER QUALITY, versus fertilizing and using pesticides
• PROVIDE FIRM FOOTING, enabling harvest, pruning, and spraying during inclement weather.
• INDIVIDUALISE EXPRESSION OF TERROIR, better than a bag of fertilizer

The first decisions that need to be made are whether the cover crop will be sown with annual tillage or not. My feeling is that tilling disturbs the soil structure and could contribute to erosion and so I'd rather not till. The next question is whether we should sow perennial or annual plants.

In the non-tillage system, the soil is tilled the first year and sown with annual seeds that then reseed themselves. The vineyard is mown in early spring and early summer and then left to its own devices. Subterranean clovers (Trifolium subterraneum) are ideal for this purpose. They are native from Ireland to Belgium, are self-pollinating and of little interest to insects, and reproduce by geocarpy, or underground seed development, a rare form of reproduction not characteristic of other clovers. It is a very popular forage crop for livestock. Rose clovers, crimson clover, red clover, berseem clover, bur medic, bolansa clover, and Persian clover are also suited for this farming system. Clover would be good for bees, too. Some grasses can also be used, but many of the perennial grasses are competitive with grapevine roots and can have a 'devigorating' effect on the vineyard. The fine fescues are least competitive and grow very short. 

Another no-till approach is planting annual cover crops that are not self-reseeding, such as oats, barley, peas and vetch. The cover crop is simply mowed and left to lie on the soil surface, usually,  just before fall rains arrive. 

One common no-till approach alternates self-reseeding annuals with annually planted and plowed down cover crops in alternate tractor rows for three years. After three years, the planting systems are switched. Otherwise, successive plantings of mustards or radishes, followed by legumes, and then by annual grains in different years keeps the soil productive and diseases and pests under control. 

Beauty crops can also be considered. A mix of annual lupine and California poppy is especially attractive and effective in returning nitrogen to the soil. Sunflowers can make spectacular displays in a vineyard.

Cover crops need nutrients to grow well. Compost made from a mixture of animal manure and grape pomace (50:50 mix)  has enough NPK to get the cover crops off to a good start. Many growers will start with one or two tons per acre. In subsequent seasons, less material will be used.

I was distressed today to learn of a study that indicates collapse of our insect populations around the world. I've certainly noticed fewer insects: no midges in Ireland for the last few years, collapse of bee colonies our own included. When I was younger, we'd be eaten alive by black flies and mosquitoes. Not so any more, but I have been moving around more. I'll have to take this factor into consideration to see if I can attract certain beneficial insects. So much to account for. I need a matrix.

All of this is so much to take in. But overall my goals are:

• To avoid use of unnatural substances
• To practice not organic but Gaia farming, showing respect and compatibility with the earth
• To develop something I am proud of and pleases me

More to come, naturally.  And happy #WomenInScience Day. I love STEM, don't you?