‘Cover crops,’ article by Monty Waldin published in Harpers Wine & Spirit, February 2002, commissioned by Tim Atkin MW.

The most diverting PR press pack I have received so far this year is from Bonterra Vineyards, described by brand owner Brown-Forman as the world’s “leading” wine brand made from organically grown grapes. What caught my eye were not the contents of the folder celebrating Bonterra’s entire range gaining Soil Association organic status in the UK, welcome though this is (see Green Space, passim), or that the pack is made from recycled materials. It was the colour illustration on the pack’s cover.

Titled “Naturally Better” the illustration shows a vine in profile, with its grape-laden leaf canopy, vine trunk and subterranean root system. It also shows cover crops growing in the area between the vine rows and explains the beneficial role they play in organic winegrowing.

The Bonterra illustration may shock those who still believe that good wine comes only from vineyards that appear to have been “immaculately farmed”. This latter phrase is often used as a term of reverence by the wine media and is code for vineyards without a weed in sight. The misguided assumption is that weeds are BAD and that bare earth between the vine rows is a sign of conscientious farming. In other words immaculately farmed vineyards signify Man is in control of Nature and thus of our wine. How reassuring.

In fact whether one is farming a First Growth or an allotment weeds should be considered good plants that, thanks to man but through no fault of their own, happen to be growing in the wrong place. So by implication cover crops can be considered as beneficial weeds introduced to the vineyard by the winegrower for specific purposes. Cover crops are not planted but are sown as seeds between the vine rows, usually in either autumn in the case of winter cover crops or spring in the case of summer ones. They are allowed to germinate and grow before being mown or ploughed in several months later. Several cover crops are usually sown together as mix, to encourage biodiversity and because different cover crops grow in different ways and at different times and so produce different effects.

For instance cover crops like clover and beans are called legumes and draw nitrogen from the air down into their roots. When legumes are ploughed in the nitrogen in the decomposing roots is released into the soil where it becomes available to the vine as a nutrient source, rendering Nitrogen-rich chemical fertilizers irrelevant. As well as influencing the soil’s chemical balance cover crops also affect its structure. Soils that have been physically compacted by vineyard machines can be loosened by sowing a cover crop like Daikon Radish that produce a long taproot. When the radish is cut back this taproot dies and leaves a hole roughly 6 inches deep by one inch wide in the ground. The holes allow rainwater to be collected, vital in hot climates like California. Were the soil between the vines allowed to remain hard and compacted the rainwater would be lost as run off and valuable topsoil would be eroded with it.

Cover crops that flower influence the biology of a vineyard. In California for example the flowers of crimson clover and bell beans provide a habitat for aphids which beneficial predators like ladybird beetles, minute pirate bugs and green lacewings like to eat. Once attracted into the vineyard these beneficial predators go on to eat leafhopper nymphs and mites which otherwise would damage the vine leaves, preventing photosynthesis and thus the ripening of the grapes. To sustain these beneficial predators a mix of different cover crops which flower one after the other is usually sown: in California mustard flowers fade just as rose clover flowers start to bloom.

Here cover crops are restoring the links in the food chain lost when pests like leafhoppers are wiped out by toxic pesticides leaving vineyard eco-systems unbalanced. However in some areas certain cover crops may not be beneficial, In Europe alfalfa builds a taproot like the Daikon radish, but in California alfalfa attracts the sharpshooter vectors of the Pierce’s Disease bacterium Xyllela fastidiosa which is lethal to vines.

High-growing cover crops like oats or barley may lower air and soil temperatures to increase the risk of frost, delay vine bud break or block sunlight from the grapes if allowed to grow up into the vine canopy. In addition cover crops require that extra cash be found to buy seed and finance the labour needed to manage them year-round.

Clever vineyard managers (and Bonterra seem to have several) are learning to manage the cover crops in such a way that they set their own seed after flowering. This reduces seed costs and the need to sow every year and thus reduces environmental impacts (tractor diesel, soil compaction).

California’s biodynamic Frey Vineyards offset the costs of cover cropping by sowing Echinacea, St John’s Wort, Valerian, Feverfew, Hyssop, Angelica, Lemon Balm, Motherwort, Self Heal and Yarrow. These plants can be harvested to make herb extracts, which can be sold. This not only generates another income-source but also allows a one-crop agricultural business to diversify. And with more crops to grow and harvest full-time employees are more easily retained throughout the year when seasonal vineyard work is short. This can make the business more efficient overall and may improve employee morale by adding variety to the workload. I’ll let you know as soon as I receive a press release from a Bordeaux First informing me it is growing garlic between the vines. But don’t hold your breath. [ends]