Frost

I've known for three years that this moment would come. Two weeks ago I drove into the field, parked up the car and set out amongst the vines to see what damage they had sustained after 4 nights in a row of temperatures as low as -1.9C.

The results were depressing but not unexpected. Leaves and bursting buds across the whole vineyard turned brown and crispy. Burnt and shrivelled. The Melon B with the largest proportion of damage because that's the earliest to start growing. The hardest hit of all being those vines that were so weak last year they were cut right back down to 2 bud level and had thus sprung prematurely to life in the little greenhouses of their rabbit guards only to be struck down by the little pools of frost that form in those same guards at night.

Damage at the bottom of the slope. Damage at the top of the slope. In field one and field 2. Where was the 2C temperature gradient I had measured on many nights from top to bottom, where my weather station is? Isn't that how radiation frost is supposed to work?

So 2024 gets off to a difficult start. Luckily it's not supposed to be a big harvest year, because if it were, well, it's not anymore.

Late frost is one of the major catastrophes that regularly visit vineyards worldwide. I've written before how you can measure the passing of the seasons by the vineyard catastrophes that strike at different times of year. Frost comes first. Then rain and cold at flowering and fruit set. Then those summer months when first powdery then downy mildew can whip through the vineyard and blight what foliage and fruit got through the frost and rain. Deer may pay a visit and strip the vineyard bare. Then as the grape clusters begin to ripen its time for botrytis, or the spotted wing drosophila, to rot what's left. If there's anything remaining at harvest time then here come the birds. Pheasants ate every single one of the small number of grape bunches I left last October on my second year vines.

Vines are frost hardy to quite low temperatures during the dormant season but as soon as the buds have started to swell and burst they become very sensitive. Early frost isn't a problem. Late frost, typically from mid April onwards in England, can wipe out not only the first leaves but the inflorescences that will later become grape clusters. Because these, rather stupidly, emerge at the same time as the first leaves. The earlier the budburst, the more risk there is of late frost. And because it takes a whole season to shift the timing of those first shoots but just one night to send them all back where they came from, the warm winters and springs that climate change has brought us perversely increase frost risk.

We had an extremely warm late winter and early spring, one of the warmest on record. Then a cold and miserable late April. But not many English vineyards suffered from frost damage? Why did I? Because I am in a frost hollow.

I should have known what I was getting myself in for when I first viewed the land: sloping steeply into a narrow valley bottom. The perfect topography for radiation frost to collect and hang around with nowhere to go. But never underestimate the power of naive optimism coupled with the encouraging results of a site frost risk survey done by a reputable vineyard site selection business. And a thriving small vineyard just down the road in the same valley. The Pett Bottom valley is very far east and surrounded in relatively close proximity by sea. It's not the Welsh Marches or Oxfordshire. But here I am, and it is objectively frostier here than in better air-drained vineyards nearby. I know because many have their own weather stations with live data online that make me seethe with envy on still clear nights.

So how best to protect against frost? The viticultural gnomes of the English wine industry will tell you that the best frost protection is to avoid a frost prone site. They are right. Thanks. But that's not much help now. Once we accept we're somewhere with frost risk a whole world - an expensive and by and large pretty labour intensive world - of frost protection options is waiting for us.

The other thing those gnomes will tell you is that there are two types of frost: radiation frost which forms in situ on still nights, as low level inversions build from the valley bottom up and cold air is unable to mix out but gets stuck near the ground; and advection frost where the whole depth of the airmass is cold and nowhere is safe. My site suffers from radiation frost. The problem is still, stable air that cannot turn over and cannot drain away.

If frost protection were all about making a pretty instagrammable photo then the choice would be easy: frost candles. Light them every few metres across the site when cold temperatures threaten, then hire a drone and take a nice aerial shot for social media safe in the knowledge the vines will be protected by the radiant warmth and the overturning air induced by the burners. Lovely, and the internet was full of these charming pictures a few weeks ago, but it means burning through huge amounts of material for hours on end on multiple nights, and it also means being there to light the things. Low capex costs but high running costs, and labour intensive.

The smoky straw fires growers on the continent use do a similar job coupled with an insulating effect from the smoke but would be the stuff of ugly neighbour disputes and letters from the council if attempted in a populated part of Southern England.

Then we have the blowers: fixed and moveable frost fans, vertical cold air sinks and other variations on the blower theme, some with heat but most relying on how the mixing of the air breaks up temperature inversions and stops radiation cooling from taking over. They can be very effective, but very noisy. And the capex cost is higher. So, with the tractor-drawn versions, is the labour. Driving around all night with a fan on the back of the tractor. And I don't live there so it's no more practical than frost candles.

On to the more expensive fixed solutions. There are two of interest: heated wires or infrared tubes on the trellising are a nice idea and growing in popularity; and irrigation: if you spray water constantly on a vineyard during a frost event the latent heat release from freezing will keep the temperature on the plant around zero and not below. A seemingly foolproof solution that works even in advection frosts. Also quite pretty in social media posts from places like Chablis most springs. But incredibly expensive. I got a quote for an irrigation system. Ouch. And I'd have needed to build a water reservoir to feed it. Not going to happen.

So for now Little Bursted Vineyard runs naked. It takes frost risk where it comes. I could make a virtue of this. It's certainly "low intervention" and doubtless saves carbon emissions. But it would be nice to have options. There are some sprays that can help build cold hardiness in vines, and a promising solution involving sprayed on foam which seems to work well so long as it doesn't rain, so I might try those next year. But hopefully next year there will be no late frosts. And no deer, no rain at flowering, no diseases, and no hungry birds.