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Wednesday, December 12, 2012

How to Prune Table Grapes

Q. I have a couple of vines of grapes. Should I cut them back so the stem is about 1 ft. high? I've been doing that and have not gotten many grapes from my Thompson plant and none from my seedless Flame. These plants are about 5 years old.

This picture was taken in the spring of 2012, about the second week of March.
You can see a grape spur in the upper right quadrant of the picture, reddish
brown, that has two leaves coming from buds . It was cut back from a much
longer stem, which grew in 2011, following the directions in this posting.
Since this grape can be spur pruned, I cut this longer stem back so that only
two buds remains on the spur. Those buds gave rise to the leaves you see.
Also coming from these buds will be growth that will form the grape clusters
or bunches. Follow this spur back to its base and you will see it connected to
a short stem, brown in color, older than the spur. This was the previous year's
spur. At the base is even older wood which has a characteristic greyish color.
A. If you continue to cut off all of last year’s (2011) vine growth, you will never have grapes. Bunches of grapes produced in 2012 come from buds on growth that was produced in 2011, the previous year. The only thing you have to do now is decide how much of the growth produced in 2012 you will leave remaining after you have finished pruning. By the way, I usually delay the final pruning of grapes until at least mid-February to avoid loss of fruit from late freezes.

Another spur which has been cut intentionally too long.
If there is damage from winter cold and the end of the
spur dies, there is enough of the spur left for it to recover.
The oldest growth at the bottom is grey. The spur on top
is reddish brown. In between is a former spur which is
brown. The spur has three buds. Bottom bud is pointy on
the bottom right of the spur. The next bud up is on the left
side where a side shoot has been cut back. The third bud is
on the top right where another side shoot was cut back.
After cold weather has passed at the mid to end of February
you would cut the spur 1/4 inch above the second bud. After
you get some experience, cut it back 1/4 inch above the
bottom bud leaving only one bud.
            Let me walk you through the steps for pruning table grapes. You can prune wine grapes this way but wine grapes should be pruned slightly different.  With wine grapes we want to be more careful to “balance” the load of fruit with the growth of the vine to get better quality grapes.

            I like to prune grapes in either one step in mid-February or a two-step process with an initial pruning of the grapes at leaf fall and a final pruning on the February date. Some people are itching to cut those grapes early and this will give them something to do. Otherwise just delay the pruning.

            There are two things to know before you begin. First, the wood where the fruit is produced is on last year’s growth which is a different color from older, nonproductive wood. It is usually more reddish. I will post pictures on my blog next week so you and others can see what I am talking about.

            Secondly, most grapes are pruned so that the amount of last year’s wood, the reddish colored wood, is only an inch or two long. But there are two table grapes that are NOT pruned like this. These are Thompson seedless and Black Monukka. These are pruned so that the remaining reddish, last year’s wood is about 12 to 18 inches long.

            When you leave just a very short length of reddish wood remaining after pruning then this is called spur pruning and this short stub of red wood is called a spur. When you leave a long piece of this reddish wood, then this is called a cane and you are cane pruning.

This is the tangle of new growth you must either remove or cut back to spurs. The new growth in the right places and spaced the right distance apart will be cut back to spurs, one or two buds in length.
            Pruning your grapes early can possibly result in no fruit production this next year in our climate. If there are some very low temperatures and strong, cold dry winds blowing across your vines after you prune it is possible to freeze back the spurs or canes and lose your crop or severely reduce it. If you delay pruning until February, you reduce that risk.

            Here is how to prune. Find the end of a stem or branch of a grape vine. Follow it until you see a place where there is a definite change in color from red to grey and the wood looks older. There is a clear separation between these two colors. This is where the 2012 growth began (red) and growth in 2011 (grey and older) ended.

            On the outside of the reddish stem you will see buds on either side. The last years red growth (on buds close to the separation of colors) is where the fruit will be produced for most grapes.

            For those grapes that require spur pruning, you can cut the reddish stem back leaving only two buds remaining. Prune ¼ inch beyond the second bud from the grey wood with a straight cut.

Another picture of one year old wood that will be cut back to either a spur
or a cane. Canes are just long spurs. Grapes like Thompson Seedless have
buds at the base of the new growth that will not produce grapes, just leaves.
So in the case of Thompson Seedless we have to cut their "spurs" extra
long so we include buds that will have fruit. Spurs are cut long enough
so that the buds that produce fruit (usually after the bottom ten buds) are
included. These extra long spurs are called "canes".
            For those grapes which should be cane pruned, like Thompson seedless, you should cut the red growth or cane so that there are ten buds remaining. Essentially it is just a much longer spur. This will leave a reddish cane in length something less than 18 inches.

            Grape vines are notorious for bleeding after they have been cut. In other words you may see water coming from the cut ends. Don’t worry about that. It is normal and will heal.

            When the vine sets small, BB-sized fruit in bunches, it is time to go ahead and remove bunches that are poorly formed or have not set berries very well or are too small.

            The remaining bunches are then pinched at the bottom, removing about 1/3 of the bunch. This increases the size of the berries that are remaining in the bunch. If your berries are small, then you did not remove enough bunches or you did not pinch the bottom of the bunch enough. Both are important.

1 comment:

  1. Could you show a picture of what you mean by pinching the bunches by 1/3. Would be very helpful.