- A new study tests whether hemp is an effective plant for intercropping between wine grapes to increase soil health and potentially add another cash crop to vineyards.
- Vintners planted hemp with other cover crops on a vineyard in New Zealand, and found that while hemp was a robust grower, it didn’t compete with grape vines for water, even in dry conditions.
- Surprisingly, the wine made from grapes grown near hemp had a delicious, complex flavor profile, but researchers say more tests are needed to see if hemp was the driving factor.
- The researchers plan to investigate further whether hemp is an effective plant for intercropping to improve vineyard soil health and carbon storage.
Producing the best wine grapes is an art: vintners need to meticulously manage soil and water conditions, deal with pests, and curate pollinators. Monitoring their vines year-round, growers carefully adjust things like irrigation, fertilizing, and planting beneficial vegetation in between rows.
It’s this last effort — the mix of cover crops between vines — that farmers leverage to both bolster crops and buffer them from climate change. Growers are planting trees for shade and microclimate protection or adding certain row crops to boost harvests and encourage pollinators. Intercropping may even add another source of income for growers.
A recent case study on a vineyard in New Zealand tested how planting hemp between grape rows might improve soil conditions while providing a secondary cash crop. After three years of testing, the researchers found there were positive benefits for both soil health and carbon storage, as well as a surprising development: the wine tasted better.
Hemp and wine
Many vineyards near Marlborough, on New Zealand’s South Island, are planted on ancient river terraces, but not all terraces have rich, fertile soil. “There’s not a lot of soil; it’s mostly rocks,” said Mark Krasnow, a plant physiologist and owner of Thoughtful Viticulture Ltd., and co-author of the study.
So Krasnow teamed up with grape grower Kirsty Harkness (of Hark & Zander Ltd.) to test how hemp planted in between rows of grapes might improve Sauvignon blanc harvests.
Part of growing cover crops, or intercropping, is to diversify the farming system and break up monocultures, said Miguel Altieri, emeritus professor of agroecology at the University of California, Berkeley.
Altieri was not involved in this study but has researched cover crops in California vineyards for years, including planting legumes mixed with cereals to not only bolster soil health, but also entice beneficial insects.
But in New Zealand they turned to hemp (Cannabis sativa), a cannabis plant used for industrial purposes like food, cosmetics, fiber and building materials. Hemp contains less than 0.3% of THC (tetrahydrocannabinol), the psychoactive component of marijuana.
“The origin of the project was just wanting to build soil,” Krasnow said. “We’ve got a vineyard with poor soil, we’ve got the potential to grow hemp there — let’s see whether these two species can coexist.”
But the very factors that make hemp appealing — fast-growing, hardy, large roots — also meant it could be a liability to the grapes. Krasnow said he was careful about what hemp to plant. “If you look at the genotypes of hemp, the fiber types tend to be ridiculously tall — the oil and seed types tend to be quite a lot shorter,” he said.
They split the vineyard into two sections: one intercropped with hemp and the other without. Krasnow sampled changes in soil compaction, organic matter and water use for both sections.
“Hemp has very deep roots and grows a lot of biomass, so it could be very competitive, much more so than other cover crop species,” he noted, adding they were particularly concerned about the hemp competing with the vines for water and nutrition.
But he found no evidence of water competition, even in the dry and daily irrigated environment.
“We didn’t see any signs of [competition] in any aspect of the canopy growth, the nutrition, the yield and berry size,” he said.
In fact, a severe drought put the hemp to the test during the experiment. “We went six weeks without any rain, which is ages here,” Krasnow said, adding that only the hemp and a few perennial weeds survived in the intercropped rows. “The real benefit I see is that hemp is very drought tolerant.”
This is good news for growers in drier climes, like the Mediterranean.
“Here, the droughts are very dramatic, very intense during the summer. But what is more frightening is that these droughts start earlier now,” said Aurélie Métay, an agronomy professor at L’Institut Agro Montpellier in France, who was not involved in the study. “If you find a species able to produce large amounts of biomass in a short period of time, with a low amount of water, that is perfect,” as adding biomass is a key factor in building a strong ecosystem.
Still, Altieri said he’s skeptical of the benefits of hemp versus other tried-and-true cover crops, such as buckwheat, wild carrot, horseradish and sunflowers, which can increase soil biodiversity, survive drought, and attract preferred insects.
“If I compare hemp with flowering cover crops like buckwheat, for example, I can guarantee that the reduction of pests would be much higher with the buckwheat as opposed to the hemp, because the hemp doesn’t have the flowers that attract the beneficial insects,” he said.
Alteri recommended comparative studies to look at hemp versus other common crops.
The research continues
Krasnow said although there were some promising developments in soil health and carbon storage, hemp also created some issues.
“In the vigorous parts of the vineyards, it got way too tall — it was getting caught in the fans of [Harkness’s] sprayer,” Krasnow said. “I certainly would not recommend this cover crop for a place that had a really rich soil.”
He also mentioned that the laws around hemp legality can make it difficult to harvest as a cash crop.
Hemp can be a valuable crop, Altieri noted, but harvesting the flowers or leaves from intercropped plantings has issues for replenishing the soil. “If you’re taking out most of the biomass, then you’re taking out the main purpose of having a cover crop.
Métay pointed out that while many growers are keen to introduce cover crops for biodiversity, they need to understand that investing in a cover crop doesn’t guarantee it will benefit the ecosystem, as the production of biomass varies significantly from year to year. “The wine grower is an expert of the vines … once you start to sow a cover crop, that means that you have to manage another crop.”
Krasnow agreed, adding that many cover crops are simply mowed. “Anything that adds more work to the vineyard manager’s plate is almost a non-starter, even if there would be tangible benefits from it.”
He said these initial findings are just preliminary. Krasnow is now expanding the research to look at carbon sequestration and integrated pest management, including combining clover with hemp and vines.
Hemp: Flavor enhancer?
But what about the effect of the hemp on the wine itself? Krasnow found the hemp didn’t compete with the grape yield or add any cannabinoids to the grapes, but may have enhanced the flavor.
“I mean, that’s the real intriguing thing to me,” Krasnow said. “I tasted these wines, and it was one of the most amazing Sauvignon Blanc I’ve ever had. To me, Sauva is often too green, too vegetal, too acidic — basically sort of underripe. This one was beautiful, amazing sort of apricot, peachy flavors, which you don’t often get.”
Like the soil health and carbon storage potential of hemp in cover crops, Krasnow said he’d like to see more studies on hemp’s potential effects on taste. “What if that season was a one-off?” He recommended looking at at least “two seasons, and generally three or four” to really tell if there’s a positive taste enhancement of the grapes.
If so, perhaps hemp could be the secret ingredient for a well-rounded wine.
Banner image: The wine made from grapes grown near hemp had a delicious, complex flavor profile, but researchers say more tests are needed to see if hemp was the driving factor. Image by Rodrigo Abreu via Unsplash (Public domain).
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