Spring frost: nightmare in the North

I bet a lot of wine growers throughout northern Europe didn’t get much sleep last Wednesday night, 19 April. The reason? Severe spring frost. This is the time when the vines start budding, making the fragile buds vulnerable to below zero temperatures.

Frost will always be a hazard in cool climates, but this time devastating temperatures of up to -10 were measured at soil level here in the South of Holland. This could potentially wipe out a complete vintage. What to do? Prey and hope for the best or go McGyver style through the vineyard, trying to combat the cold?

Over winter, vines are dormant and so hardy they can resist frost. No problem there. It is the time of spring when budbreak arrives and it can still actually snow in April, as Prince once sang.

Due to the cold, solutes in the plant cells freeze, forming ice crystals and damaging the plant’s green tissue that comes out of a bud. If too much damaged, the vine’s buds will not flower and no grapes will grow.

Before the frost creeps in, a grower could train the vines higher up the wires to avoid cold from the ground. S/he could also try and prune a bit later, using the fact that buds at the end of a vine cane develop earlier than at the vine’s head. If you wait with pruning, you leave more buds on a cane than necessary.

If frost happens, the buds at the end of the cane could be damaged, but they will be cut off by pruning, keeping only the buds you need. This could work for small wineries, but due to the amount of pruning work, this is obviously not an option for larger scale vineyards.

If frost hits the vineyards, no vintner will nose dive under the duvet

Once the cold comes in, there isn’t really that much you can do in the vineyard. If the vineyard is on a slope, the cold air will flow to the bottom of the hill. A hedge or fence at the bottom may be aesthetically fitting, in terms of frost prevention it is a bad idea as they create frost pockets by blocking the cold air from draining way. Trimming is key here.

Slope or not, when frost is happening, no grower will nose dive under the duvet but instead will keep a close watch at his/her precious vines. It must be weird to drive until the wee hours through the vineyard with tractor and blower, mixing warmer upper layers of air with lower cold air.

Other growers might go high tech and spray anti-frost stuff, hoping to lower the frost risk with a couple of degrees. At approx. €100 per ha this solution is quite cheap, but lacking enough scientific proof it actually works. Keep the fire burning, is the mantra at other vineyards where fire pots or burners provide enough heat to keep the cold out. A rather expensive solution with relatively limited impact.

Most growers will sprinkle the vines. The water will freeze, releasing some heat and keeping the temperature around the buds at zero degrees. Effective but quite an impact on water resources, as it takes probably the whole night to keep sprinkling and 1 ha needs about 30,000 litres per hour!

Besides the environmental considerations, the downside for growers in the South of Holland is that the ground water is too deep to use. Many fruit growers here lost a substantial amount of this year’s potential harvest. Following last year’s August rain and less yield, many will struggle to survive.

At Pietershof, vintner Albert drove the tractor at 4 AM, mixing the air in the vine rows. While checking the buds today, it was interesting to witness the concept of micro climate again. The buds at the bottom of the hill were still closed and seemed to have some damage, while bud break at the top of the hill had already taken place. And that is only 100 metres apart!

Albert’s guestimate is 10-15% frost damage, but a proper assessment can only be made once all the buds will break and green leaves appear instead of brown. Fingers crossed!

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