"Bleeding" in Grapevines
Late pruning towards the end of winter - as recommended for frosty regions - usually leads to "bleeding" of the cut surfaces or "wounds." This is not a negative process for the vine, however, one must prevent the sap from flowing down along the stem framework onto buds below and "drowning" them, as this will stop them from breaking in spring.
From about February, vines are again in sap, the vine draws water with enormous force from as far as 30m below. This water presses against the freshly cut surfaces which haven't callused yet, and oozes from there. This "bleeding" may last up to 2 weeks, and occasionally it develops into small runlets along the stem. Whether the draconian expression "bleeding" is appropriate is anyone's guess, but it is assumed that low concentrations of minerals and sugars - the vine's frost protection - are also flushed out with the water, which in case of further severe frosts can significantly damage the vine.
It is essential to prevent the sap from flowing down along the canes and "drowning" vital buds. Through skillful Cutting Techniques ie cutting the wood at a slight angle one can achieve a definite spillover spot, from where the water will run off exactly between the buds below. Alternatively, long canes can be slightly bent downwards or a small thread tied behind the cut surface to facilitate draining.
- Water oozing from a cut spur ("Bleeding"). Here the cane is bending downwards, which will allow the water to drain unimpeded and without damaging the fruit buds on the cane.
- A larger cut surface. After a while, the oozing liquid will turn into a gelatinous substance and eventually dry up.
