Outdoor Grapes

The upper Don valley has some of the highest farmalnd in Britain. Despite being in the "grey" zone on the mean summer temperature map (see Background), Growth Degree Day heat totals within the shelter of the garden are more akin to those of "pink" zone areas. Vineyards in the latter zone have been successfully tried as far north as Northumberland. It was therefore to try 'outdoor' grapes. They are not the first to be grown this far north though - outdoor grapes were reported in Buckie on the coast of Moray  in 1933 [Aberdeen Press and Journal, 1933, Grapes in the open at Buckie. Tuesday August 23rd, p.8.].

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Initially it was decided to grow the outdoor vines as low bushes supported by individual stakes within a walled-garden setting. Several varities were planted at a spacing of 4ft (above) with the intention of pruning the bushes to short rods overwinter. Frost protection was envisaged with sealed tree-protection tubes slotted over the rods during budburst. At 800ft altitude with a location near the valley floor, Spring frosts here can be severe, minus 5C is quite common in late April-early May. Siting higher up the valley sides would have made little differences as the  ubes provided next to no protection: The air in the tube thermally equilibrated with the ambient air temperature within an hour of the tube being positioned, with the resultant level of frost damage depending on the cold tolerance of the vine variety and the stage of budding reached at the time of frosting. I lost two of the supposedly fastest ripening grape varieties this way - Solaris and Hasansky Sladky (aka. Baltica) - both theses varieties it seems need a long season for maturation of the year's wood, and once frosted, the time avaliable after the opening of the seconday buds was not enough for this process.

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The idea of siting the vines in shallow trenches came from an internet article about grape growing in Moscow. But it was in use  long before that, the Reverend Phillip LeBroq advocated growing vines in trenches (albeit very much wider and deeper) in 1692 to cope to cope with the temperatures of the Little Ice Age. The trenches then were covered with  with oiled canvas when frost threatened. I aim to try that sometime, but up till now, 3mm twinwall poly carbonate has been used as covering. The vines are pruned to very short rods with canes (1-2ft in length) folded beneath the covers which  are weighted down with stones, when frost threatens. The covered trenches act as a pit-greenhouse. Tests in February 2014 showed that temperatures could be maintained above 0 C in the trench with frost temperatures as low as as minus 7 C. 

   The logic behind the north-south alighnment of trenches was to maximise solar warming of the soil. In reality, I don't think it made much difference, and later trences were aligned east-west along the south-southwest facing slope. Various linings to the trenches were tried. Paving slabs as linings (lower left) seemed to cool the trenches on the often cloudy days. Wood lined trenches (above, with newly planted Jublienka Novgoroda vines in 2015) worked ok but eventially rotted. Unlined trenches were easy to make but prone to caving and weeds tended to grow in the walls.

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Typically, budburst occurs in late April in the trench-grown vines. The covers are removed when the frost risk passes, and the vines then trained up temporary supports (e.g. canes) inserted into the ground around the edges of the trenches. The method is effective, but time-consuming, so is probably not suitable to large-scale commercial application.

Flowering of outdoor vines usually occurs in the last week of June, and the fastest  grape varieties such as Zilga (above) and Dalnivostock Ramming are ripe by mid September.

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Outdoor temperatures usually show a marked decline from 10th September each year, but varieties such as Michurinets (above, pictured on 2/10/18 when it had reached 15.7 degrees Brix) will ripen in warmer years.